Helicopter Flying Handbook (FAA-H-8083-21B)

11-1

Introduction

Today, helicopters are quite reliable. However, emergencies

do occur, whether a result of mechanical failure or pilot

error, and should be anticipated. Regardless of the cause, the

recovery needs to be quick and precise. By having a thorough

knowledge of the helicopter and its systems, a pilot is able

to handle the situation more readily. Helicopter emergencies

and the proper recovery procedures should be discussed and,

when possible, practiced in flight. In addition, by knowing

the conditions that can lead to an emergency, many potential

accidents can be avoided.

Helicopter Emergencies and

Hazards

Chapter 11

11-2

Normal Powered Flight Autorotation

Direction of flight

Figure 11-1. During an autorotation, the upward flow of relative wind permits the main rotor blades to rotate at their normal speed. In

effect, the blades are “gliding” in their rotational plane.

Several factors affect the rate of descent in autorotation:

bank angle, density altitude, gross weight, rotor rpm, trim

condition, and airspeed. The primary ways to control the rate

of descent are with airspeed and rotor rpm. Higher or lower

airspeed is obtained with the cyclic pitch control just as in

normal powered flight. In theory, a pilot has a choice in the

angle of descent, varying, from straight vertical to maximum

horizontal range (which is the minimum angle of descent).

Rate of descent is high at zero airspeed and decreases to a

minimum at approximately 50–60 knots, depending upon the

particular helicopter and the factors just mentioned. As the

airspeed increases beyond that which gives minimum rate

of descent, the rate of descent increases again.

When landing from an autorotation, the only energy available

to arrest the descent rate and ensure a soft landing is the

kinetic energy stored in the rotor blades. Tip weights can

greatly increase this stored energy. A greater amount of

rotor energy is required to stop a helicopter with a high

rate of descent than is required to stop a helicopter that is

descending more slowly. Therefore, autorotative descents

at very low or very high airspeeds are more critical than

those performed at the minimum rate of descent airspeed.

Refer to the height/velocity diagram discussion in Chapter

7, Helicopter Performance.

Each type of helicopter has a specific airspeed and rotor rpm

at which a power-off glide is most efficient. The specific

airspeed is somewhat different for each type of helicopter,

but certain factors affect all configurations in the same

manner. In general, rotor rpm maintained in the low green

area (see Figure 5-3) gives more distance in an autorotation.

Heavier helicopter weights may require more collective to

control rotor rpm. Some helicopters need slight adjustments

to minimum rotor rpm settings for winter versus summer

Autorotation

In a helicopter, an autorotative descent is a power-off

maneuver in which the engine is disengaged from the

main rotor disk and the rotor blades are driven solely by

the upward flow of air through the rotor. [Figure 11-1] In

other words, the engine is no longer supplying power to

the main rotor.

The most common reason for an autorotation is failure of the

engine or drive line, but autorotation may also be performed

in the event of a complete tail rotor failure, since there is

virtually no torque produced in an autorotation. In both

cases, maintenance has often been a contributing factor to the

failure. Engine failures are also caused by fuel contamination

or exhaustion as well resulting in a forced autorotation.

If the engine fails, the freewheeling unit automatically

disengages the engine from the main rotor, allowing it to

rotate freely. Essentially, the freewheeling unit disengages

anytime the engine revolutions per minute (rpm) is less than

the rotor rpm.

At the instant of engine failure, the main rotor blades are

producing lift and thrust from their angle of attack (AOA)

and velocity. By lowering the collective (which must be done

immediately in case of an engine failure), lift and drag are

reduced, and the helicopter begins an immediate descent,

thus producing an upward flow of air through the rotor disk.

This upward flow of air through the rotor disk provides

sufficient thrust to maintain rotor rpm throughout the descent.

Since the tail rotor is driven by the main rotor transmission

during autorotation, heading control is maintained with the

antitorque pedals as in normal flight.

11-3

conditions, and high altitude versus sea level flights. For

specific autorotation airspeed and rotor rpm combinations for

a particular helicopter, refer to the Rotorcraft Flight Manual

(RFM). The specific airspeed and rotor rpm for autorotation

is established for each type of helicopter based on average

weather, calm wind conditions, and normal loading. When

the helicopter is operated with heavy loads in high density

altitude or gusty wind conditions, best performance is

achieved from a slightly increased airspeed in the descent.

For autorotation at low density altitude and light loading,

best performance is achieved from a slight decrease in

normal airspeed. Following this general procedure of fitting

airspeed and rotor rpm to existing conditions, a pilot can

achieve approximately the same glide angle in any set of

circumstances, and thereby estimate the touchdown point

accurately.

It is important that pilots experience autorotations from

various airspeeds. This provides better understanding of

the necessary flight control inputs to achieve the desired

airspeed, rotor rpm and autorotation performance, such

as the maximum glide or minimum descent airspeed. The

decision to use the appropriate airspeed and rotor rpm for

the given conditions should be instinctive to reach a suitable

landing area. The helicopter glide ratio is much less than

that of a fixed-wing aircraft and takes some getting used to.

The flare to land at 80 knots indicated airspeed (KIAS) will

be significantly greater than that from 55 KIAS. Rotor rpm

control is critical at these points to ensure adequate rotor

energy for cushioning the landing.

Use collective pitch control to manage rotor rpm. If rotor rpm

builds too high during an autorotation, raise the collective

sufficiently to decrease rpm back to the normal operating

range, then reduce the collective to maintain proper rotor rpm.

If the collective increase is held too long, the rotor rpm may

decay rapidly. The pilot would have to lower the collective

in order to regain rotor rpm. If the rpm begins decreasing,

the pilot must again lower the collective. Always keep the

rotor rpm within the established recommended range for the

helicopter being flown.

RPM Control

Rotor rpm in low inertia rotor systems has been studied

in simulator flight evaluations which indicate that the

simultaneous application of aft cyclic, down collective,

and alignment with the relative wind (trim) at a wide range

of airspeeds, including cruise airspeeds, is critical for all

operations during the entry of an autorotation. The applicable

Rotorcraft Flight Manual (RFM) should be consulted to

determine the appropriate procedure(s) for safely entering an

autorotation. This is vitally important since the procedure(s)

for safely entering an autorotation may vary with specific

makes and/or models of helicopters. A basic discussion of

the aerodynamics and control inputs for single rotor systems

is in order here.

Helicopter pilots must understand the use of the collective

for rotor rpm control during power off autorotations in a turn.

Upward movement of the collective reduces the rpm and

downward movement increases the rpm. Cyclic movement

is primarily associated with attitude/airspeed control in

powered flight but may not be given the credit appropriate

for rotor rpm control during practice and emergency power

off autorotations. As long as the line of cyclic movement is

parallel with the flight path of the helicopter (trimmed), the

aft movement of the cyclic also creates greater air flow up

through the bottom of the rotor disk and contributes to an

increase in rotor rpm. If the flight path is 10 degrees to the

right of the longitudinal axis of the helicopter, theoretically,

the cyclic should be moved 10 degrees aft and left of the

longitudinal axis to get maximum air up through the rotor

system.

As the pilot lowers the collective in reaction to a loss of

power during cruise flight there may be a tendency for the

nose of the helicopter to pitch down. As a result, the pilot may

tend to lean forward slightly, which delays the application

of simultaneous aft cyclic to prevent the pitch change and

associated loss of rotor rpm. A slight gain in altitude at cruise

airspeed during the power off entry into an autorotation

should not be of great concern as is the case for the execution

of practice or actual quick stops.

Various accident investigations have concluded that, when

faced with a real power failure at cruise airspeed, pilots are

not simultaneously applying down collective, aft cyclic, and

antitorque pedal inputs in a timely manner. Low inertia rotor

systems store less kinetic energy during autorotation and, as

a result, rotor rpm decays rapidly during deceleration and

touchdown. Conversely, less energy is required to regain

safe rotor rpm during autorotation entry and autorotative

descent. The pilot should immediately apply simultaneous

down collective, aft cyclic and trim the helicopter for entry

into an autorotation initiated at cruise airspeed. If rotor rpm

has been allowed to decrease, or has inadvertently decreased

below acceptable limits, an application of aft cyclic may

help rebuild rotor rpm. This application of aft cyclic must

be made at least at a moderate rate and may be combined

with a turn, either left or right, to increase airflow through

the rotor system. This will work to increase rotor rpm. Care

should be maintained to not over-speed the rotor system as

this is attempted.

Risk Management during Autorotation Training

The following sections describe enhanced guidelines for

autorotations during rotorcraft/helicopter flight training,

as stated in Advisory Circular (AC) 61-140. There are

11-4

Figure 11-2. Straight-in autorotation.

risks inherent in performing autorotations in the training

environment, and in particular the 180-degree autorotation.

This section describes an acceptable means, but not the

only means, of training applicants for a rotorcraft/helicopter

airman certificate to meet the qualifications for various

rotorcraft/helicopter ratings. You may use alternate methods

for training if you establish that those methods meet the

requirements of the Helicopter Flying Handbook (HFH),

FAA practical test standards (PTS), and the Rotorcraft Flight

Manual (RFM).

Straight-In Autorotation

A straight-in autorotation is one made from altitude with

no turns. Winds have a great effect on an autorotation.

Strong headwinds cause the glide angle to be steeper due

to the slower groundspeed. For example, if the helicopter

is maintaining 60 KIAS and the wind speed is 15 knots,

then the groundspeed is 45 knots. The angle of descent will

be much steeper, although the rate of descent remains the

same. The speed at touchdown and the resulting ground run

depend on the groundspeed and amount of deceleration. The

greater the degree of deceleration, or flare, and the longer

it is held, the slower the touchdown speed and the shorter

the ground run. Caution must be exercised at this point as

the tail rotor will be the component of the helicopter closest

to the ground. If timing is not correct and a landing attitude

not set at the appropriate time, the tail rotor may contact the

ground causing a forward pitching moment of the nose and

possible damage to the helicopter.

A headwind is a contributing factor in accomplishing a slow

touchdown from an autorotative descent and reduces the

amount of deceleration required. The lower the speed desired

at touchdown, the more accurate the timing and speed of the

flare must be, especially in helicopters with low-inertia rotor

disks. If too much collective is applied too early during the

final stages of the autorotation, the kinetic energy may be

depleted, resulting in little or no cushioning effect available.

This could result in a hard landing with corresponding

damage to the helicopter. It is generally better practice to

accept more ground run than a harder landing with minimal

groundspeed. As proficiency increases, the amount of ground

run may be reduced.

Technique (How to Practice)

Refer to Figure 11-2 (position 1). From level flight at

the appropriate airspeed (cruise or the manufacturer’s

recommended airspeed), 500–700 feet above ground level

(AGL), and heading into the wind, smoothly but firmly

lower the collective to the full down position. Use aft cyclic

to prevent a nose low attitude while maintaining rotor rpm

in the green arc with collective. If the collective is in the

full down position, the rotor rpm is then being controlled by

the mechanical pitch stops. During maintenance, the rotor

stops must be set to allow minimum autorotational rpm with

a light loading. This means that collective will still be able

to be reduced even under conditions of extreme reduction of

vertical loading (e.g., very low helicopter weight, at very low-

density altitude). After entering an autorotation, collective

pitch must be adjusted to maintain the desired rotor rpm.

Coordinate the collective movement with proper antitorque

pedal for trim, and apply cyclic control to maintain proper

airspeed. Once the collective is fully lowered, decrease

throttle to ensure a clean split/separation of the needles. This

means that the rotor rpm increases to a rate higher than that of

the engine—a clear indication that the freewheeling unit has

allowed the engine to disconnect. After splitting the needles,

readjust the throttle to keep engine rpm above normal idling

speed, but not high enough to cause rejoining of the needles.

See the RFM for the manufacturer's recommendations for

autorotation rate of descent.

At position 2, adjust attitude with cyclic to obtain the

manufacturer’s recommended autorotation (or best gliding)

speed. Adjust collective as necessary to maintain rotor rpm

in the lower part of the green arc (see page 11-2). Aft cyclic

movements cause an increase in rotor rpm, which is then

controlled by a small increase in collective. Avoid a large

collective increase, which results in a rapid decay of rotor

rpm, and leads to “chasing the rpm.” Avoid looking straight

down in front of the aircraft. Continually crosscheck attitude,

trim, rotor rpm, and airspeed.

At the altitude recommended by the manufacturer (position

3), begin the flare with aft cyclic to reduce forward airspeed

and decrease the rate of descent. Maintain heading with the

antitorque pedals. During the flare, maintain rotor rpm in

11-5

the green range. In the execution of the flare, care must be

taken that the cyclic be moved rearward neither so abruptly

that it causes the helicopter to climb, nor so slowly that it

fails to arrest the descent, which may allow the helicopter

to settle so rapidly that the tail rotor strikes the ground. In

most helicopters, the proper flare attitude is that resulting in a

groundspeed of a slow run. When forward motion decreases

to the desired groundspeed—usually the lowest possible

speed (position 4)—move the cyclic forward to place the

helicopter in the proper attitude for landing.

This action gives the student an idea of airframe attitude to

avoid, because a pilot should never allow ground contact

unless the helicopter is more nose-low than that attitude.

Limiting the flare to that attitude may result in slightly faster

touchdown speeds but will eliminate the possibility of tail

rotor impact on level surfaces.

The landing gear height at this time should be approximately

3–15 feet AGL, depending on the altitude recommended by

the manufacturer. As the apparent groundspeed and altitude

decrease, the helicopter must be returned to a more level

attitude for touchdown by applying forward cyclic. Some

helicopters can be landed on the heels in a slightly nose high

attitude to help decrease the forward groundspeed, whereas

others must land skids or landing gear level, in order to spread

the landing loads equally to all of the landing gear. Extreme

caution should be used to avoid an excessive nose high and

tail low attitude below 10 feet. The helicopter must be close

to the landing attitude to keep the tail rotor from contacting

the surface.

At this point, if a full touchdown landing is to be performed,

allow the helicopter to descend vertically (position 5). This

collective application uses some of the kinetic energy in the

rotor disk to help slow the descent rate of the helicopter.

When the collective is raised, the opposite antitorque pedal

used in powered flight will be needed due to the friction

within the transmission/drive train. Touch down in a level

flight attitude.

Control response with increased pitch angles will be slightly

different than normal. With a decrease in main rotor rpm,

the antitorque authority is reduced (the pedals react more

slowly), requiring larger control inputs to maintain heading

at touchdown.

Some helicopters, such as the Schweitzer 300, have a canted

tail stabilizer. With a canted stabilizer, it is crucial that the

pilot apply the appropriate pedal input at all times during the

autorotation. If not the tailboom tends to swing to the right,

which allows the canted stabilizer to raise the tail. This can

result in a severe nose tuck which is quickly corrected with

right pedal application.

A power recovery can be made during training in lieu of a full

touchdown landing. Refer to the section on power recovery

for the correct technique.

After the helicopter has come to a complete stop after

touchdown, lower the collective pitch to the full-down

position. Do not try to stop the forward ground run with aft

cyclic, as the main rotor blades can strike the tail boom. By

lowering the collective slightly during the ground run, an

increase in weight is placed on the landing carriage, slowing

the helicopter; however, this is dependent on the condition

of the landing surface.

One common error is the holding of the helicopter off the

surface, versus cushioning it onto the surface during an

autorotation. Holding the helicopter in the air by using all of

the rotor rpm kinetic energy usually causes the helicopter to

have a hard landing, which results in the blades flexing down

and contacting the tail boom. The rotor rpm should be used

to cushion the helicopter on to the surface for a controlled,

smooth landing instead of allowing the helicopter to drop

the last few inches.

Common Errors

1. Not understanding the importance of an immediate

entry into autorotation upon powerplant or driveline

failure.

2. Failing to use sufficient antitorque pedal when power

is reduced.

3. Lowering the nose too abruptly when power is

reduced, thus placing the helicopter in a dive.

4. Failing to maintain proper rotor rpm during the

descent.

5. Applying up-collective pitch at an excessive altitude,

resulting in a hard landing, loss of heading control,

and possible damage to the tail rotor and main rotor

blade stops.

6. Failing to level the helicopter or achieve the

manufacturers preferred landing attitude.

7. Failing to minimize or eliminate lateral movement

during ground contact. (Similar for items 8 and 9)

8. Failing to maintain ground track in the air and keeping

the landing gear aligned with the direction of travel

during touchdown and ground contact.

9. Failing (in a practice run) to go around if not within

limits and specified criteria for safe autorotation.

11-6

Autorotation with Turns

Turns (or a series of turns) can be made during autorotation

to facilitate landing into the wind or avoiding obstacles.

Turns during autorotation should be made early so that the

remainder of the autorotation is flown identically to a straight-

in autorotation. The most common turns in an autorotation

are 90 degrees and 180 degrees. The following technique

describes an autorotation with a 180-degree turn.

The pilot establishes the aircraft on a downwind heading

at the recommended airspeed, and parallel to the intended

touchdown point. Then, taking the wind into account, the pilot

establishes the ground track approximately 200 feet laterally

from the desired course line to the touchdown point. In strong

crosswind conditions, the pilot should be prepared to adjust

the downwind leg closer or farther out, as appropriate. The

pilot uses the autorotation entry airspeed recommended by

the RFM. When abeam the intended touchdown point, the

pilot smoothly reduces collective, then reduces power to the

engine to show a split between the rotor rpm and engine rpm

and simultaneously applies appropriate anti-torque pedal

and cyclic to maintain proper attitude/airspeed. Throughout

the autorotation, the pilot should continually crosscheck the

helicopter’s attitude, rotor rpm, airspeed, and verify that the

helicopter is in trim (centered trim ball).

After the descent and autorotation airspeed is established, the

pilot initiates the 180-degree turn. For training operations,

initially roll into a bank of at least 30 degrees, but no more

than 60 degrees. It is important to maintain the proper

airspeed, rotor rpm, and trim (centered trim ball) throughout

the turn. Changes in the helicopter’s attitude and the angle

of bank causes a corresponding change in rotor rpm within

normal limits. Do not allow the nose to pitch up or down

excessively during the maneuver, as it may cause undesirable

rotor rpm excursions.

Pitot-static airspeed indications may be unreliable or lag

during an autorotational turn. The pilot should exercise

caution to avoid using excessive aircraft pitch attitudes and to

avoid chasing airspeed indications in an autorotational turn.

Note: Approaching the 90-degree point, check the position of

the landing area. The second 90 degrees of the turn should

end with a roll-out on a course line to the landing area. If the

helicopter is too close, decrease the bank angle (to increase

the radius of turn); if too far out, increase the bank angle

(to decrease the radius of the turn). A bank angle of no more

than 60 degrees should be encountered during this turn.

Monitor the trim ball (along with one’s kinesthetic sense)

and adjust as necessary with cyclic and anti-torque pedal

to maintain coordinated flight. Prior to passing through

200 feet above ground level (AGL), if landing or making a

surface-level power recovery, the turn should be completed,

and the helicopter aligned with the intended touchdown

area. Upon reaching the course line, set the appropriate

crosswind correction. If the collective pitch was increased

to control the rpm, it may need to be lowered on rollout to

prevent decay in rotor rpm.

This maneuver should be aborted at any point the following

criteria is not met: if the helicopter is not in a stabilized

approach to landing profile (i.e., it is not aligned as close

as possible into the wind with the touchdown point, after

completing the 180-degree turn); if the rotor rpm is not within

limits; if the helicopter is not at a proper attitude/airspeed; or

if the helicopter is not under proper control at 200 feet AGL.

It is essential that the pilot on the controls (or a certificated

flight instructor (CFI), when intervening) immediately abort

the maneuver and execute a smooth power recovery and go-

around. It is important for the CFI who is intervening at this

point to remember that the go-around is a far safer option than

trying to recover lost rotor rpm and reestablish or recover to

the hover or even the preferred hover taxi.

From all entry positions, but particularly true of the

180-degree entry, a primary concern is getting the aircraft

into the course line with as much altitude as possible. Once

the collective has been lowered and the engine set to flight

idle, the helicopter will lose altitude. A delayed turn will

result in a lower altitude when arriving on the course line.

Additionally, an uncoordinated flight condition (trim-ball

not centered) results in an increased sink rate, which may

be unrecoverable if not corrected.

During the turn to the course line, the pilot should use a

scan pattern to see outside as well as inside the cockpit. Of

primary importance outside is maintaining the appropriate

descending attitude and a proper turn rate. Essential items to

scan inside are rotor rpm and centered trim ball. Rotor rpm

will build anytime “G” forces are applied to the rotor system.

Usually, this occurs in the turn to the course line and during

the deceleration flare.

Throughout the maneuver, rotor rpm should be maintained

in the range recommended in the RFM. Rotor rpm outside

of the recommended range results in a higher rate of descent

and less glide-ratio. When the rotor rpm exceeds the desired

value as a result of increased G load in the turn, timely

use of up collective will increase the pitch of the blades

and slow the rotor to the desired rpm. In an autorotation,

rotor rpm is the most critical element, as it provides the lift

required to stabilize an acceptable rate of descent and the

energy necessary to cushion the landing. Collective should

be lowered to the full down position to maintain rotor rpm

immediately following a loss of power. However, rapid or

11-7

abrupt collective movement could lead to mast bumping in

some rotorcraft with teetering rotor systems.

Energy is a very important property of all rotating

components, and the kinetic energy stored in the rotor system

is used to cushion the landing. More lift is produced at the

bottom of an autorotation by raising the collective, which

increases the angle of attack of the blades. The rotor rpm will

also rapidly decay at this point and it is essential to properly

time the flare and the final collective pull to fully arrest the

descent and cushion the landing. Upon arriving into the

course line prior to the flare, the scan should focus almost

entirely outside. The scan should include:

• The horizon for attitude, ground track, and nose

alignment;

• the altitude to set the flare and for closure (groundspeed);

and

• the instrument cross-check of airspeed, rotor rpm, and

engine rpm in the descent.

Every autorotational flare will be different depending on the

existing wind conditions, airspeed, density altitude (DA),

and the aircraft gross weight. A pilot operating a helicopter

at a high DA needs to take into account the effects on the

control of the helicopter when recovering from an aborted

autorotation.

Some effects to consider are:

• Higher rate of descent.

• Reduced rotor rpm builds in autorotation.

• Low initial rotor rpm response in autorotation.

• The requirement for a higher flare height.

• Reduced engine power performance.

Common Errors

The following common errors should be prevented:

1. Entering the maneuver at an improper altitude or

airspeed.

2. Entering the maneuver without a level attitude (or not

in coordinated flight).

3. Entering the maneuver and not correcting from the

initial deceleration to a steady state attitude (which

allows excessive airspeed loss in the descent).

4. Improper transition into the descent on entry.

5. Improper use of anti-torque on entry.

6. Failure to establish the appropriate crosswind

correction, allowing the aircraft to drift.

7. Failure to maintain coordinated flight through the tum.

8. Failure to maintain rotor rpm within the RFM

recommended range.

9. Excessive yaw when increasing collective to slow rate

of descent during power recovery autorotations.

10. During power recovery autorotations, a delay in

reapplying power.

11. Initial collective pull either too high or too low.

12. Improper flare (too much or not enough).

13. Flaring too low or too high (AGL).

14. Failure to maintain heading when reapplying power.

15. Not landing with a level attitude.

16. Landing with aircraft not aligned with the direction

of travel.

17. Insufficient collective cushioning during full

autorotations.

18. Abrupt control inputs on touchdown during full

autorotations.

Practice Autorotation with a Power Recovery

A power recovery is used to terminate practice autorotations

at a point prior to actual touchdown. After the power

recovery, a landing can be made or a go-around initiated.

Technique (How to Practice)

At approximately 3–15 feet landing gear height AGL,

depending upon the helicopter being used, begin to level the

helicopter with forward cyclic control. Avoid excessive nose-

high, tail-low attitude below 10 feet. Just prior to achieving

level attitude, with the nose still slightly up, coordinate

upward collective pitch control with an increase in the

throttle to join the needles at operating rpm. The throttle and

collective pitch must be coordinated properly.

If the throttle is increased too fast or too much, an engine

overspeed can occur; if throttle is increased too slowly or too

little in proportion to the increase in collective pitch, a loss of

rotor rpm results. Use sufficient collective pitch to stop the

descent, but keep in mind that the collective pitch application

must be gradual to allow for engine response. Coordinate

proper antitorque pedal pressure to maintain heading. When

a landing is to be made following the power recovery, bring

the helicopter to a hover and then descend to a landing.

In nearly all helicopters, when practicing autorotations with

power recovery, the throttle should be at the flight setting at

the beginning of the flare. As the rotor disk begins to dissipate

its energy, the engine is up to speed as the needles join when

the rotor decreases into the normal flight rpm.

11-8

Helicopters that do not have the throttle control located on

the collective are generally exceptions to basic technique

and require some additional prudence. The autorotation

should be initiated with the power levers left in the “flight,”

or normal, position. If a full touchdown is to be practiced, it

is common technique to move the power levers to the idle

position once the landing area can safely be reached. In most

helicopters, the pilot is fully committed at that point to make

a power-off landing. However, it may be possible to make

a power recovery prior to passing through 100 feet AGL if

the powerplant can recover within that time period and the

instructor is very proficient. The pilot should comply with

the RFM instructions in all cases.

When practicing autorotations to a power recovery, the

differences between reciprocating engines and turbines

may be profound. The reciprocating powerplant generally

responds very quickly to power changes, especially power

increases. Some turbines have delay times depending on

the type of fuel control or governing system installed. Any

reciprocating engine needing turbocharged boost to develop

rated horse power may have significant delays to demands

for increased power, such as in the power recovery. Power

recovery in those helicopters with slower engine response

times must have the engines begin to develop enough power

to rejoin the needles by approximately 100 feet AGL.

If a go-around is to be made, the cyclic control should be

moved forward to resume forward flight. In transition from

a practice autorotation to a go-around, exercise caution to

avoid an altitude-airspeed combination that would place the

helicopter in an unsafe area of its height/velocity diagram.

This is one of the most difficult maneuvers to perform due to

the concentration needed when transitioning from powered

flight to autorotation and then back again to powered flight.

For helicopters equipped with the power control on the

collective, engine power must be brought from flight power

to idle power and then back to a flight power setting. A delay

during any of these transitions can seriously affect rotor rpm

placing the helicopter in a situation that cannot be recovered.

The cyclic must be adjusted to maintain the required

airspeed without power, and then used for the deceleration

flare, followed by the transition to level hovering flight.

Additionally, the cyclic must be adjusted to remove the

compensation for translating tendency. The tail rotor is

no longer needed to produce antitorque thrust until almost

maximum power is applied to the rotor disk for hovering

flight, when the tail rotor must again compensate for the main

rotor torque, which also demands compensation for the tail

rotor thrust and translating tendency.

The pedals must be adjusted from a powered flight anti-

torque trim setting to the opposite trim setting to compensate

for transmission drag and any unneeded vertical fin thrust

countering the now nonexistent torque and then reset to

compensate for the high power required for hovering flight.

All of the above must be accomplished during the 23 seconds

of the autorotation, and the quick, precise control inputs must

be made in the last 5 seconds of the maneuver.

Common Errors

1. Initiating recovery too late, which requires a rapid

application of controls and results in overcontrolling.

2. Failure to obtain and maintain a level attitude near the

surface.

3. Failure to coordinate throttle and collective pitch

properly, which results in either an engine overspeed

or a loss of rotor rpm.

4. Failure to coordinate proper antitorque pedal with the

increase in power.

5. Late engine power engagement causing excessive

temperature or torque, or rpm drop.

6. Failure to go around if not within limits and specified

criteria for safe autorotation.

Practicing Power Failure in a Hover

Power failure in a hover, also called hovering autorotation, is

practiced so that a pilot can automatically make the correct

response when confronted with engine stoppage or certain

other emergencies while hovering. The techniques discussed

in this section are for helicopters with a counterclockwise

rotor disk and an antitorque rotor.

Technique (How to Practice)

To practice hovering autorotation, establish a normal

hovering height (approximately 2–3 feet) for the particular

helicopter being used, considering load and atmospheric

conditions. Keep the helicopter headed into the wind and

hold maximum allowable rpm.

To simulate a power failure, firmly roll the throttle to the

engine idle position. This disengages the driving force of the

engine from the rotor, thus eliminating torque effect. As the

throttle is closed, apply proper antitorque pedal to maintain

heading. Usually, a slight amount of right cyclic control is

necessary to keep the helicopter from drifting to the left, to

compensate for the loss of tail rotor thrust. However, use

cyclic control, as required, to ensure a vertical descent and

a level attitude. Do not adjust the collective on entry.

11-9

Helicopters with low inertia rotor disks settle immediately.

Keep a level attitude and ensure a vertical descent with cyclic

control while maintaining heading with the pedals. Any lateral

movement must be avoided to prevent dynamic rollover. As

rotor rpm decays, cyclic response decreases, so compensation

for the winds will require more cyclic input. At approximately

1 foot AGL, apply upward collective control, as necessary,

to slow the descent and cushion the landing without arresting

the rate of descent above the surface. Usually, the full amount

of collective is required just as the landing gear touches the

surface. As upward collective control is applied, the throttle

must be held in the idle detent position to prevent the engine

from re-engaging. The idle detention position is a ridged stop

position between idle and off in which the idle release button

snaps into, prevent accidental throttle off.

Helicopters with high-inertia rotor disks settle more slowly

after the throttle is closed. In this case, when the helicopter has

settled to approximately 1 foot AGL, apply upward collective

control while holding the throttle in the idle detent position

to slow the descent and cushion the landing. The timing of

collective control application and the rate at which it is applied

depend upon the particular helicopter being used, its gross

weight, and the existing atmospheric conditions. Cyclic control

is used to maintain a level attitude and to ensure a vertical

descent. Maintain heading with antitorque pedals.

When the weight of the helicopter is entirely resting on

the landing gear, cease application of upward collective.

When the helicopter has come to a complete stop, lower the

collective pitch to the full-down position.

The timing of the collective movement is a very important

consideration. If it is applied too soon, the remaining rpm may

not be sufficient to make a soft landing. On the other hand,

if it is applied too late, surface contact may be made before

sufficient blade pitch is available to cushion the landing.

The collective must not be used to hold the helicopter off

the surface, causing a blade stall. Low rotor rpm and ensuing

blade stall can result in a total loss of rotor lift, allowing the

helicopter to fall to the surface and possibly resulting in blade

strikes to the tail boom and other airframe damage such as

landing gear damage, transmission mount deformation, and

fuselage cracking.

Common Errors

1. Failure to use sufficient proper antitorque pedal when

power is reduced.

2. Failure to stop all sideward or backward movement

prior to touchdown.

3. Failure to apply up-collective pitch properly, resulting

in a hard touchdown.

4. Failure to touch down in a level attitude.

5. Failure to roll the throttle completely to idle.

6. Failure to hover at a safe altitude for the helicopter

type, atmospheric conditions, and the level of training/

proficiency of the pilot.

7. Failure to go around if not within limits and specified

criteria for safe autorotation.

Vortex Ring State

Vortex ring state (formerly referenced as settling-with-

power) describes an aerodynamic condition in which a

helicopter may be in a vertical descent with 20 percent up to

maximum power applied, and little or no climb performance.

The previously used term settling-with-power came from the

fact that the helicopter keeps settling even though full engine

power is applied.

In a normal out-of-ground-effect (OGE) hover, the helicopter

is able to remain stationary by propelling a large mass of air

down through the main rotor. Some of the air is recirculated

near the tips of the blades, curling up from the bottom of

the rotor disk and rejoining the air entering the rotor from

the top. This phenomenon is common to all airfoils and is

known as tip vortices. Tip vortices generate drag and degrade

airfoil efficiency. As long as the tip vortices are small, their

only effect is a small loss in rotor efficiency. However, when

the helicopter begins to descend vertically, it settles into its

own downwash, which greatly enlarges the tip vortices. In

this vortex ring state, most of the power developed by the

engine is wasted in circulating the air in a doughnut pattern

around the rotor.

In addition, the helicopter may descend at a rate that exceeds

the normal downward induced-flow rate of the inner blade

sections. As a result, the airflow of the inner blade sections is

upward relative to the disk. This produces a secondary vortex

ring in addition to the normal tip vortices. The secondary

vortex ring is generated about the point on the blade where the

airflow changes from up to down. The result is an unsteady

turbulent flow over a large area of the disk. Rotor efficiency

is lost even though power is still being supplied from the

engine. [Figure 11-3]

A fully developed vortex ring state is characterized by an

unstable condition in which the helicopter experiences

uncommanded pitch and roll oscillations, has little or no

collective authority, and achieves a descent rate that may

approach 6,000 feet per minute (fpm) if allowed to develop.

A vortex ring state may be entered during any maneuver

that places the main rotor in a condition of descending in a

column of disturbed air and low forward airspeed. Airspeeds

11-10

Figure 11-3. Vortex ring state.

that are below translational lift airspeeds are within this

region of susceptibility to vortex ring state aerodynamics.

This condition is sometimes seen during quick-stop type

maneuvers or during recovery from autorotation.

The following combination of conditions is likely to cause

settling in a vortex ring state in any helicopter:

1. A vertical or nearly vertical descent of at least 300

fpm. (Actual critical rate depends on the gross weight,

rpm, density altitude, and other pertinent factors.)

2. The rotor disk must be using some of the available

engine power (20–100 percent).

3. The horizontal velocity must be slower than effective

translational lift.

Situations that are conducive to a vortex ring state condition

are attempting to hover OGE without maintaining precise

altitude control, and approaches, especially steep approaches,

with a tailwind component.

When recovering from a vortex ring state condition, the pilot

tends first to try to stop the descent by increasing collective

pitch. However, this only results in increasing the stalled

area of the rotor, thereby increasing the rate of descent. Since

inboard portions of the blades are stalled, cyclic control

may be limited. The traditional recovery is accomplished

by increasing airspeed, and/or partially lowering collective

to exit the vortex. In most helicopters, lateral cyclic thrust

combined with an increase in power and lateral antitorque

thrust will produce the quickest exit from the hazard. This

technique, known as the Vuichard Recovery (named after the

Swiss examiner from the Federal Office of Civil Aviation

who developed it) recovers by eliminating the descent rate as

opposed to exiting the vortex. If the vortex ring state and the

corresponding descent rate is allowed to progress to what is

called the windmill brake state, the point where the airflow

is completely up through the rotor, the only recovery may

be an autorotation.

Tandem rotor helicopters should maneuver laterally to

achieve clean air in both rotors at the same time.

For vortex ring state demonstrations and training in

recognition and recovery should be performed from a safe

altitude to allow recovery no less than 1000 feet AGL or the

manufacturer’s recommended altitude, whichever is higher.

To enter the maneuver, come to an OGE hover, maintaining

little or no airspeed (any direction), decrease collective

to begin a vertical descent, and as the turbulence begins,

increase collective. Then allow the sink rate to increase to 300

fpm or more as the attitude is adjusted to obtain airspeed of

less than 10 knots. When the aircraft begins to shudder, the

application of additional up collective increases the vibration

and sink rate. As the power is increased, the rate of sink of

the aircraft in the column of air will increase.

If altitude is sufficient, some time can be spent in the

vortices, to enable the pilot to develop a healthy knowledge

of the maneuver. However, helicopter pilots would normally

initiate recovery at the first indication of vortex ring state.

Recovery should be initiated at the first sign of vortex ring

state by applying forward cyclic to increase airspeed and/ or

simultaneously reducing collective. The recovery is complete

when the aircraft passes through effective translational lift

and a normal climb is established.

Common Errors—Traditional Recovery

1. Too much lateral speed for entry into vortex ring state.

2. Excessive decrease of collective.

Common Errors—Vuichard Recovery

1. Excessive lateral cyclic

2. Failure to maintain heading

Retreating Blade Stall

In forward flight, the relative airflow through the main rotor

disk is different on the advancing and retreating side. The

relative airflow over the advancing side is higher due to the

forward speed of the helicopter, while the relative airflow on

the retreating side is lower. This dissymmetry of lift increases

as forward speed increases.

To generate the same amount of lift across the rotor disk,

the advancing blade flaps up while the retreating blade flaps

down. This causes the AOA to decrease on the advancing

11-11

116°

122°

Figure 11-4. Ground resonance.

blade, which reduces lift, and increase on the retreating blade,

which increases lift. At some point as the forward speed

increases, the low blade speed on the retreating blade, and

its high AOA cause a stall and loss of lift.

Retreating blade stall is a factor in limiting a helicopter’s

never-exceed speed (V

) and its development can be felt

by a low frequency vibration, pitching up of the nose, and

a roll in the direction of the retreating blade. High weight,

low rotor rpm, high density altitude, turbulence and/or

steep, abrupt turns are all conducive to retreating blade stall

at high forward airspeeds. As altitude is increased, higher

blade angles are required to maintain lift at a given airspeed.

Thus, retreating blade stall is encountered at a lower forward

airspeed at altitude. Most manufacturers publish charts and

graphs showing a V

decrease with altitude.

When recovering from a retreating blade stall condition

caused by high airspeed, moving the cyclic aft only worsens

the stall as aft cyclic produces a flare effect, thus increasing

the AOA. Pushing forward on the cyclic also deepens

the stall as the AOA on the retreating blade is increased.

While the first step in a proper recovery is usually to reduce

collective, RBS should be evaluated in light of the relevant

factors discussed in the previous paragraph and addressed

accordingly. For example, if a pilot at high weight and high

DA is about to conduct a high reconnaissance prior to a

confined area operation where rolling into a steep turn causes

onset of RBS, the recovery is to roll out of the turn. If the

cause is low rotor rpm, then increase the rpm.

Common Errors

1. Failure to recognize the combination of contributing

factors leading to retreating blade stall.

2. Failure to compute V

limits for altitudes to be flown.

Ground Resonance

Helicopters with articulating rotors (usually designs with

three or more main rotor blades) are subject to ground

resonance, a destructive vibration phenomenon that occurs

at certain rotor speeds when the helicopter is on the ground.

Ground resonance is a mechanical design issue that results

from the helicopter’s airframe having a natural frequency that

can be intensified by an out-of-balance rotor. The unbalanced

rotor disk vibrates at the same frequency (or multiple thereof)

of the airframe’s resonant frequency, and the harmonic

oscillation increases because the engine is adding power

to the system, increasing the magnitude (amplitude) of the

vibrations until the structure or structures fail. This condition

can cause a helicopter to self-destruct in a matter of seconds.

Hard contact with the ground on one corner (and usually

with wheel-type landing gear) can send a shockwave to

the main rotor head, resulting in the blades of a three-blade

rotor disk moving from their normal 120° relationship to

each other. This movement occurs along the drag hinge and

could result in something like 122°, 122°, and 116° between

blades. [Figure 11-4] When another part of the landing gear

strikes the surface, the unbalanced condition could be further

aggravated.

If the rpm is low, the only corrective action to stop ground

resonance is to close the throttle immediately and fully lower

the collective to place the blades in low pitch. If the rpm is in

the normal operating range, fly the helicopter off the ground,

and allow the blades to rephase themselves automatically.

Then, make a normal touchdown. If a pilot lifts off and allows

the helicopter to firmly re-contact the surface before the

blades are realigned, a second shock could move the blades

again and aggravate the already unbalanced condition. This

could lead to a violent, uncontrollable oscillation.

This situation does not occur in rigid or semi-rigid rotor

disks because there is no drag hinge. In addition, skid-type

landing gear is not as prone to ground resonance as wheel-

type landing gear, since the rubber tires' resonant frequency

typically can match that of the spinning rotor, unlike the

condition of a rigid landing gear.

Dynamic Rollover

A helicopter is susceptible to a lateral rolling tendency,

called dynamic rollover, when it is in contact with the surface

11-12

Tail rotor thrust

Tip-path plane neutral cyclic

Tip-path plane full left cyclic

Bank

angle

Pivot point

Weight

Main rotor thrust

Figure 11-5. Forces acting on a helicopter with right skid on the

ground.

during takeoffs or landings. For dynamic rollover to occur,

some factor must first cause the helicopter to roll or pivot

around a skid or landing gear wheel, until its critical rollover

angle is reached. The angle at which dynamic rollover

occurs will vary based on helicopter type. Then, beyond

this point, main rotor thrust continues the roll and recovery

is impossible. After this angle is achieved, the cyclic does

not have sufficient range of control to eliminate the thrust

component and convert it to lift. If the critical rollover angle

is exceeded, the helicopter rolls on its side regardless of the

cyclic corrections made.

Dynamic rollover begins when the helicopter starts to pivot

laterally around its skid or wheel. For dynamic rollover to

occur the following three factors must be present:

1. A rolling moment

2. A pivot point other than the helicopter’s normal CG

3. Thrust greater than weight

This can occur for a variety of reasons, including the failure

to remove a tie down or skid-securing device, or if the skid

or wheel contacts a fixed object while hovering sideward,

or if the gear is stuck in ice, soft asphalt, or mud. Dynamic

rollover may also occur if you use an improper landing or

takeoff technique or while performing slope operations.

Whatever the cause, dynamic rollover is possible if not using

the proper corrective technique.

Once started, dynamic rollover cannot be stopped by

application of opposite cyclic control alone. For example,

the right skid contacts an object and becomes the pivot point

while the helicopter starts rolling to the right. Even with full

left cyclic applied, the main rotor thrust vector and its moment

follows the aircraft as it continues rolling to the right. Quickly

reducing collective pitch is the most effective way to stop

dynamic rollover from developing. Dynamic rollover can

occur with any type of landing gear and all types of rotor disks.

It is important to remember rotor blades have a limited range

of movement. If the tilt or roll of the helicopter exceeds that

range (5–8°), the controls (cyclic) can no longer command a

vertical lift component and the thrust or lift becomes a lateral

force that rolls the helicopter over. When limited rotor blade

movement is coupled with the fact that most of a helicopter’s

weight is high in the airframe, another element of risk is added

to an already slightly unstable center of gravity. Pilots must

remember that in order to remove thrust, the collective must

be lowered as this is the only recovery technique available.

Critical Conditions

Certain conditions reduce the critical rollover angle, thus

increasing the possibility for dynamic rollover and reducing

the chance for recovery. The rate of rolling motion is also

a consideration because, as the roll rate increases, there is

a reduction of the critical rollover angle at which recovery

is still possible. Other critical conditions include operating

at high gross weights with thrust (lift) approximately equal

to the weight.

Refer to Figure 11-5. The following conditions are most

critical for helicopters with counterclockwise rotor rotation:

1. Right side skid or landing wheel down, since

translating tendency adds to the rollover force.

2. Right lateral center of gravity (CG).

3. Crosswinds from the left.

4. Left yaw inputs.

For helicopters with clockwise rotor rotation, the opposite

conditions would be true.

Cyclic Trim

When maneuvering with one skid or wheel on the ground,

care must be taken to keep the helicopter cyclic control

carefully adjusted. For example, if a slow takeoff is attempted

and the cyclic is not positioned and adjusted to account for

translating tendency, the critical recovery angle may be

exceeded in less than two seconds. Control can be maintained

if the pilot maintains proper cyclic position and does not

allow the helicopter’s roll and pitch rates to become too

great. Fly the helicopter into the air smoothly while keeping

movements of pitch, roll, and yaw small; do not allow any

abrupt cyclic pressures.

11-13

Tail rotor thrust

Area of critical rollover

Horizontal

Slope

Full opposite cyclic limit

to prevent rolling motion

Figure 11-6. Upslope rolling motion.

Tail rotor thrust

Area of critical rollover

Horizontal

Slope

Full opposite cyclic limit

to prevent rolling motion

Figure 11-7. Downslope rolling motion.

Normal Takeoffs and Landings

Dynamic rollover is possible even during normal takeoffs and

landings on relatively level ground, if one wheel or skid is on

the ground and thrust (lift) is approximately equal to the weight

of the helicopter. If the takeoff or landing is not performed

properly, a roll rate could develop around the wheel or skid

that is on the ground. When taking off or landing, perform the

maneuver smoothly and carefully adjust the cyclic so that no

pitch or roll movement rates build up, especially the roll rate.

If the bank angle starts to increase to an angle of approximately

5–8°, and full corrective cyclic does not reduce the angle, the

collective should be reduced to diminish the unstable rolling

condition. Excessive bank angles can also be caused by landing

gear caught in a tie down strap, or a tie down strap still attached

to one side of the helicopter. Lateral loading imbalance (usually

outside published limits) is another contributing factor.

Slope Takeoffs and Landings

During slope operations, excessive application of cyclic

control into the slope, together with excessive collective pitch

control, can result in the downslope skid or landing wheel

rising sufficiently to exceed lateral cyclic control limits, and

an upslope rolling motion can occur. [Figure 11-6]

When performing slope takeoff and landing maneuvers, follow

the published procedures and keep the roll rates small. Slowly

raise the downslope skid or wheel to bring the helicopter level,

and then lift off. During landing, first touch down on the

upslope skid or wheel, then slowly lower the downslope skid

or wheel using combined movements of cyclic and collective.

If the helicopter rolls approximately 5–8° to the upslope side,

decrease collective to correct the bank angle and return to level

attitude, then start the landing procedure again.

Use of Collective

The collective is more effective in controlling the rolling

motion than lateral cyclic, because it reduces the main rotor

thrust (lift). A smooth, moderate collective reduction, at a

rate of less than approximately full up to full down in two

seconds, may be adequate to stop the rolling motion. Take

care, therefore, not to dump collective at an excessively high

rate, as this may cause a main rotor blade to strike the fuselage.

Additionally, if the helicopter is on a slope and the roll starts

toward the upslope side, reducing collective too fast may create

a high roll rate in the opposite direction. When the upslope skid

or wheel hits the ground, the dynamics of the motion can cause

the helicopter to bounce off the upslope skid or wheel, and the

inertia can cause the helicopter to roll about the downslope

ground contact point and over on its side. [Figure 11-7]

Under normal conditions on a slope, the collective should

not be pulled suddenly to get airborne because a large and

abrupt rolling moment in the opposite direction could occur.

Excessive application of collective can result in the upslope

skid or wheel rising sufficiently to exceed lateral cyclic

control limits. This movement may be uncontrollable. If the

helicopter develops a roll rate with one skid or wheel on the

ground, the helicopter can roll over on its side.

Precautions

To help avoid dynamic rollover:

1. Always practice hovering autorotations into the wind,

and be wary when the wind is gusty or greater than 10

knots.

2. Use extreme caution when hovering close to fences,

sprinklers, bushes, runway/taxi lights, tiedown cables,

deck nets, or other obstacles that could catch a skid or

wheel. Aircraft parked on hot asphalt overnight might

find the landing gear sunk in and stuck as the ramp

cooled during the evening.

11-14

3. Always use a two-step lift-off. Pull in just enough

collective pitch control to be light on the skids

or landing wheels and feel for equilibrium, then

gently lift the helicopter into the air. 4.

Hover high enough to have adequate skid or landing

wheel clearance from any obstacles when practicing

hovering maneuvers close to the ground, especially

when practicing sideways or rearward flight.

5. Remember that when the wind is coming from

the upslope direction, less lateral cyclic control is

available.

6. Avoid tailwind conditions when conducting slope

operations.

7. Remember that less lateral cyclic control is available

due to the translating tendency of the tail rotor when

the left skid or landing wheel is upslope. (This is true

for counterclockwise rotor disks.)

8. Keep in mind that the lateral cyclic requirement changes

when passengers or cargo are loaded or unloaded.

9. Be aware that if the helicopter utilizes interconnecting

fuel lines that allow fuel to automatically transfer from

one side of the helicopter to the other, the gravitational

flow of fuel to the downslope tank could change the

CG, resulting in a different amount of cyclic control

application to obtain the same lateral result.

10. Do not allow the cyclic limits to be reached. If the

cyclic control limit is reached, further lowering of the

collective may cause mast bumping. If this occurs,

return to a hover and select a landing point with a

lesser degree of slope.

11. During a takeoff from a slope, begin by leveling the

main rotor disk with the horizon or very slightly into

the slope to ensure vertical lift and only enough lateral

thrust to prevent sliding on the slope. If the upslope

skid or wheel starts to leave the ground before the

downslope skid or wheel, smoothly and gently lower

the collective and check to see if the downslope skid or

wheel is caught on something. Under these conditions,

vertical ascent is the only acceptable method of lift-off.

12. Be aware that dynamic rollover can be experienced

during flight operations on a floating platform if the

platform is pitching/rolling while attempting to land

or takeoff. Generally, the pilot operating on floating

platforms (barges, ships, etc.) observes a cycle of seven

during which the waves increase and then decrease to

a minimum. It is that time of minimum wave motion

that the pilot needs to use for the moment of landing

or takeoff on floating platforms. Pilots operating from

floating platforms should also exercise great caution

concerning cranes, masts, nearby boats (tugs) and nets.

Low-G Conditions and Mast Bumping

“G” is an abbreviation for acceleration due to the earth’s

gravity. A person standing on the ground or sitting in an

aircraft in level flight is experiencing one G. An aircraft in a

tight, banked turn with the pilot being pressed into the seat

is experiencing more than one G or high-G conditions. A

person beginning a downward ride in an elevator or riding

down a steep track on a roller coaster is experiencing less

than one G or low-G conditions. The best way for a pilot to

recognize low G is a weightless feeling similar to the start

of a downward elevator ride.

Helicopters rely on positive G to provide much or all of their

response to pilot control inputs. The pilot uses the cyclic

to tilt the rotor disk, and, at one G, the rotor is producing

thrust equal to aircraft weight. The tilting of the thrust

vector provides a moment about the center of gravity to

pitch or roll the fuselage. In a low-G condition, the thrust

and consequently the control authority are greatly reduced.

Although their control ability is reduced, multi-bladed (three

or more blades) helicopters can generate some moment

about the fuselage independent of thrust due to the rotor

hub design with the blade attachment offset from the center

of rotation. However, helicopters with two-bladed teetering

rotors rely entirely on the tilt of the thrust vector for control.

Therefore, low-G conditions can be catastrophic for two-

bladed helicopters.

At lower speeds, such as initiation of a takeoff from hover

or the traditional recovery from vortex ring state, forward

cyclic maneuvers do not cause low G and are safe to perform.

However, an abrupt forward cyclic input or pushover in

a two-bladed helicopter can be dangerous and must be

avoided, particularly at higher speeds. During a pushover

from moderate or high airspeed, as the helicopter noses over,

it enters a low-G condition. Thrust is reduced, and the pilot

has lost control of fuselage attitude but may not immediately

realize it. Tail rotor thrust or other aerodynamic factors will

often induce a roll. The pilot still has control of the rotor disk,

and may instinctively try to correct the roll, but the fuselage

does not respond due to the lack of thrust. If the fuselage is

rolling right, and the pilot puts in left cyclic to correct, the

combination of fuselage angle to the right and rotor disk

angle to the left becomes quite large and may exceed the

clearances built into the rotor hub. This results in the hub

contacting the rotor mast, which is known as mast bumping.

[Figure 11-8] Low-G mast bumping has been the cause of

numerous military and civilian fatal accidents. It was initially

encountered during nap-of-the-earth flying, a very low-

altitude tactical flight technique used by the military where

11-15

Figure 11-8. Result of improper corrective action in a low-G

condition.

the aircraft flies following the contours of the geographical

terrain. The accident sequence may be extremely rapid, and

the energy and inertia in the rotor system can sever the mast

or allow rotor blades to strike the tail or other portions of

the helicopter.

Turbulence, especially severe downdrafts, can also cause a

low-G condition and, when combined with high airspeed,

may lead to mast bumping. Typically, helicopters handle

turbulence better than a light airplane due to smaller

surface area of the rotor blades. During flight in turbulence,

momentary excursions in airspeed, altitude, and attitude are

to be expected. Pilots should respond with smooth, gentle

control inputs and avoid overcontrolling. Most importantly,

pilots should slow down, as mast bumping is less likely at

lower airspeeds.

Pilots can avoid mast bumping accidents as follows:

• Avoid abrupt forward cyclic inputs in two-bladed

helicopters. Airplane pilots may find this a difficult

habit to break because pushing the nose down is an

accepted collision avoidance maneuver in an airplane.

Helicopter pilots would accomplish the same rapid

descent by lowering the collective, and airplane pilots

should train to make this instinctual.

• Recognize the weightless feeling associated with the

onset of low G and quickly take corrective action

before the situation becomes critical.

• Recognize that uncommanded right roll for helicopters

with main rotors which rotate counter-clockwise when

viewed from above indicates that loss of control is

imminent, and immediate corrective action must be

taken.

• Recover from a low-G situation by first gently

applying aft cyclic to restore normal G before

attempting to correct any roll.

• If turbulence is expected or encountered, reduce power

and use a slower than normal cruise speed. Turbulence

(where high rotor flapping angles are already present),

and higher airspeeds (where the controls are more

sensitive) both increase susceptibility to low-G

conditions.

• Use a flight simulator to learn to recognize and

experience low G conditions that result in mast

bumping, its correct recovery technique, and the

consequences of using incorrect recovery actions.

Refer to Chapter 14, Simulation.

Multi-bladed rotors may experience a phenomenon similar

to mast bumping known as droop stop pounding if flapping

clearances are exceeded, but because they retain some control

authority at low G, occurrences are less common than for

teetering rotors.

Low Rotor RPM and Rotor Stall

Rotor rpm is a critically important parameter for all helicopter

operations. Just as airplanes will not fly below a certain

airspeed, helicopters will not fly below a certain rotor

rpm. Safe rotor rpm ranges are marked on the helicopter’s

tachometer and specified in the RFM. If the pilot allows the

rotor rpm to fall below the safe operating range, the helicopter

is in a low rpm situation. If the rotor rpm continues to fall,

the rotor will eventually stall.

Rotor stall should not be confused with retreating blade stall,

which occurs at high forward speeds and over a small portion

of the retreating blade tip. Retreating blade stall causes

vibration and control problems, but the rotor is still very

capable of providing sufficient lift to support the weight of

the helicopter. Rotor stall, however, can occur at any airspeed,

and the rotor quickly stops producing enough lift to support

the helicopter, causing it to lose lift and descend rapidly.

Rotor stall is very similar to the stall of an airplane wing

at low airspeeds. The airplane wing relies on airspeed to

produce the required airflow over the wing, whereas the

helicopter relies on rotor rpm. As the airspeed of the airplane

decreases or the speed of the helicopter rotor slows down, the

AOA of the wing/rotor blade must be increased to support

the weight of the aircraft. At a critical angle (about 15°),

the airflow over the wing or the rotor blade will separate

and stall, causing a sudden loss of lift and increase in drag

(refer to Chapter 2, Aerodynamics of Flight). An airplane

pilot recovers from a stall by lowering the nose to reduce the

AOA and adding power to restore normal airflow over the

wing. However, the falling helicopter is experiencing upward

11-16

airflow through the rotor disk, and the resulting AOA is so

high that even full down collective will not restore normal

airflow. In the helicopter when the rotor stalls, it does not do

so symmetrically because any forward airspeed will produce

a higher airflow on the advancing side than on the retreating

side. This causes the retreating blade to stall first, and its

weight makes it descend as it moves aft while the advancing

blade is climbing as it goes forward. The resulting low aft

blade and high forward blade become a rapid aft tilting of

the rotor disc sometimes referred to as rotor “blow back” or

“flap back.” As the helicopter begins to descend, the upward

flow of air acting on the bottom surfaces of the tail boom

and any horizontal stabilizers tend to pitch the aircraft nose

down. These two effects, combined with any aft cyclic by

the pilot attempting to keep the aircraft level, allow the rotor

blades to blow back and contact the tail boom, in some cases

actually severing the tail boom. Since the tail rotor is geared

to the main rotor, in many helicopters the loss of main rotor

rpm also causes a significant loss of tail rotor thrust and a

corresponding loss of directional control.

Rotor stalls in helicopters are not recoverable. At low altitude,

rotor stall will result in an accident with significant damage

to the helicopter, and at altitudes above approximately 50

feet the accident will likely be fatal. Consequently, early

recognition of the low rotor rpm condition and proper

recovery technique is imperative.

Low rotor rpm can occur during power-off and power-on

operations. During power-off flight, a low rpm situation

can be caused by the failure to quickly lower the collective

after an engine failure or by raising the collective at too

great a height above ground at the bottom of an autorotation.

However, more common are power-on rotor stall accidents.

These occur when the engine is operating normally but the

pilot demands more power than is available by pulling up

too much on the collective. Known as “overpitching,” this

can easily occur at higher density altitudes where the engine

is already producing its maximum horsepower and the pilot

raises the collective. The corresponding increased AOA of

the blades requires more engine horsepower to maintain the

speed of the blades; however, the engine cannot produce any

additional horsepower, so the speed of the blades decreases.

A similar situation can occur with a heavily loaded helicopter

taking off from a confined area. Other causes of a power-on

low rotor rpm condition include the pilot rolling the throttle

the wrong way in helicopters not equipped with a governor

or a governor failure in helicopters so equipped.

As the rpm decreases, the amount of horsepower the engine

can produce also decreases. Engine horsepower is directly

proportional to its rpm, so a 10 percent loss in rpm due

to overpitching, or one of the other scenarios above, will

result in a 10 percent loss in the engine’s ability to produce

horsepower, making recovery even slower and more difficult

than it would otherwise be. With less power from the engine

and less lift from the decaying rotor rpm, the helicopter will

start to settle. If the pilot raises the collective to stop the

settling, the situation will feed upon itself rapidly leading

to rotor stall.

There are a number of ways the pilot can recognize the low

rotor rpm situation. Visually, the pilot can not only see the

rotor rpm indicator decrease but also the change in torque

will produce a yaw; there will also be a noticeable decrease in

engine noise, and at higher airspeeds or in turns, an increase in

vibration. Many helicopters have a low rpm warning system

that alerts the pilot to the low rotor rpm condition.

To recover from the low rotor rpm condition the pilot must

simultaneously lower the collective, increase throttle if

available and apply aft cyclic to maintain a level attitude.

At higher airspeeds, additional aft cyclic may be used to

help recover lost rpm. Recovery should be accomplished

immediately before investigating the problem and must be

practiced to become a conditioned reflex.

System Malfunctions

By following the manufacturer’s recommendations regarding

operating limits and procedures and periodic maintenance

and inspections, many system and equipment failures can

be eliminated. Certain malfunctions or failures can be traced

to some error on the part of the pilot; therefore, appropriate

flying techniques and use of threat and error management

may help to prevent an emergency

Antitorque System Failure

Antitorque failure usually falls into one of two categories.

One is failure of the power drive portion of the tail rotor disk

resulting in a complete loss of antitorque. The other category

covers mechanical control failures prohibiting the pilot from

changing or controlling tail rotor thrust even though the tail

rotor may still be providing antitorque thrust.

Tail rotor drive system failures include driveshaft failures,

tail rotor gearbox failures, or a complete loss of the tail rotor

itself. In any of these cases, the loss of antitorque normally

results in an immediate spinning of the helicopter’s nose. The

helicopter spins to the right in a counterclockwise rotor disk

and to the left in a clockwise system. This discussion is for a

helicopter with a counterclockwise rotor disk. The severity of

the spin is proportionate to the amount of power being used

and the airspeed. An antitorque failure with a high-power

setting at a low airspeed results in a severe spinning to the

11-17

right. At low power settings and high airspeeds, the spin is

less severe. High airspeeds tend to streamline the helicopter

and keep it from spinning.

If a tail rotor failure occurs, power must be reduced in order to

reduce main rotor torque. The techniques differ depending on

whether the helicopter is in flight or in a hover, but ultimately

require an autorotation. If a complete tail rotor failure occurs

while hovering, enter a hovering autorotation by rolling off

the throttle. If the failure occurs in forward flight, enter a

normal autorotation by lowering the collective and rolling

off the throttle. If the helicopter has enough forward airspeed

(close to cruising speed) when the failure occurs, and

depending on the helicopter design, the vertical stabilizer

may provide enough directional control to allow the pilot to

maneuver the helicopter to a more desirable landing sight.

Applying slight cyclic control opposite the direction of yaw

compensates for some of the yaw. This helps in directional

control, but also increases drag. Care must be taken not to

lose too much forward airspeed because the streamlining

effect diminishes as airspeed is reduced. Also, more altitude is

required to accelerate to the correct airspeed if an autorotation

is entered at a low airspeed.

The throttle or power lever on some helicopters is not located

on the collective and readily available. Faced with the loss

of antitorque, the pilot of these models may need to achieve

forward flight and let the vertical fin stop the yawing rotation.

With speed and altitude, the pilot will have the time to set

up for an autorotative approach and set the power control

to idle or off as the situation dictates. At low altitudes, the

pilot may not be able to reduce the power setting and enter

the autorotation before impact.

A mechanical control failure limits or prevents control of tail

rotor thrust and is usually caused by a stuck or broken control

rod or cable. While the tail rotor is still producing antitorque

thrust, it cannot be controlled by the pilot. The amount of

antitorque depends on the position at which the controls jam or

fail. Once again, the techniques differ depending on the amount

of tail rotor thrust, but an autorotation is generally not required.

The specific manufacturer’s procedures should always be

followed. The following is a generalized description of

procedures when more specific procedures are not provided.

Landing—Stuck Left Pedal

A stuck left pedal (high power setting), which might be

experienced during takeoff or climb conditions, results in

the left yaw of the helicopter nose when power is reduced.

Rolling off the throttle and entering an autorotation only

makes matters worse. The landing profile for a stuck left

pedal is best described as a normal-to-steep approach angle to

arrive approximately 2–3 feet landing gear height above the

intended landing area as translational lift is lost. The steeper

angle allows for a lower power setting during the approach

and ensures that the nose remains to the right.

Upon reaching the intended touchdown area and at the

appropriate landing gear height, increase the collective

smoothly to align the nose with the landing direction and

cushion the landing. A small amount of forward cyclic is

helpful to stop the nose from continuing to the right and

directs the aircraft forward and down to the surface. In certain

wind conditions, the nose of the helicopter may remain

to the left with zero to near zero groundspeed above the

intended touchdown point. If the helicopter is not turning,

simply lower the helicopter to the surface. If the nose of the

helicopter is turning to the right and continues beyond the

landing heading, roll the throttle toward flight idle, which is

the amount necessary to stop the turn while landing. Flight

idle is an engine rpm in flight at a given altitude with the

throttle set to the minimum, or idle, position. The flight

idling rpm typically increase with an increase in altitude.

If the helicopter is beginning to turn left, the pilot should

be able to make the landing prior to the turn rate becoming

excessive. However, if the turn rate begins to increase prior

to the landing, simply add power to make a go-around and

return for another landing.

Landing—Stuck Neutral or Right Pedal

The landing profile for a stuck neutral or a stuck right pedal

is a low-power approach terminating with a running or roll-

on landing. The approach profile can best be described as a

shallow to normal approach angle to arrive approximately

2–3 feet landing gear height above the intended landing

area with a minimum airspeed for directional control. The

minimum airspeed is one that keeps the nose from continuing

to yaw to the right.

Upon reaching the intended touchdown area and at the

appropriate landing gear height, reduce the throttle as

necessary to overcome the yaw effect if the nose of the

helicopter remains to the right of the landing heading. The

amount of throttle reduction will vary based on power applied

and winds. The higher the power setting used to cushion the

landing, the more the throttle reduction will be. A coordinated

throttle reduction and increased collective will result in a very

smooth touchdown with some forward groundspeed. If the

nose of the helicopter is to the left of the landing heading,

a slight increase in collective or aft cyclic may be used to

align the nose for touchdown. The decision to land or go

around has to be made prior to any throttle reduction. Using

airspeeds slightly above translational lift may be helpful to

11-18

ensure that the nose does not continue yawing to the right. If

a go-around is required, increasing the collective too much or

too rapidly with airspeeds below translational lift may cause

a rapid spinning to the right.

Once the helicopter has landed and is sliding/rolling to a

stop, the heading can be controlled with a combination of

collective, cyclic and throttle. To turn the nose to the right,

raise the collective or apply aft cyclic. The throttle may be

increased as well if it is not in the full open position. To turn

the nose to the left, lower the collective or apply forward

cyclic. The throttle may be decreased as well if it is not

already at flight idle.

Loss of Tail Rotor Effectiveness (LTE)

Loss of tail rotor effectiveness (LTE) or an unanticipated

yaw is defined as an uncommanded, rapid yaw towards the

advancing blade which does not subside of its own accord.

It can result in the loss of the aircraft if left unchecked. It is

very important for pilots to understand that LTE is caused

by an aerodynamic interaction between the main rotor and

tail rotor and not caused from a mechanical failure. Some

helicopter types are more likely to encounter LTE due to the

normal certification thrust produced by having a tail rotor

that, although meeting certification standards, is not always

able to produce the additional thrust demanded by the pilot.

A helicopter is a collection of compromises. Compare the

size of an airplane propeller to that of a tail rotor. Then,

consider the horsepower required to run the propeller. For

example, a Cessna 172P is equipped with a 160-horsepower

(HP) engine. A Robinson R-44 with a comparably sized tail

rotor is rated for a maximum of 245 HP. If you assume the

tail rotor consumes 50 HP, only 195 HP remains to drive

the main rotor. If the pilot were to apply enough collective

to require 215 HP from the engine, and enough left pedal to

require 50 HP for the tail rotor, the resulting engine overload

would lead to one of two outcomes: slow down (reduction

in rpm) or premature failure. In either outcome, antitorque

would be insufficient and total lift might be less than needed

to remain airborne.

Every helicopter design requires some type of antitorque

system to counteract main rotor torque and prevent spinning

once the helicopter lifts off the ground. A helicopter is heavy,

and the powerplant places a high demand on fuel. Weight

penalizes performance, but all helicopters must have an

antitorque system, which adds weight. Therefore, the tail

rotor is certified for normal flight conditions. Environmental

forces can overwhelm any aircraft, rendering the inherently

unstable helicopter especially vulnerable.

As with any aerodynamic condition, it is very important for

pilots to not only to understand the definition of LTE, but

more importantly, how and why it happens, how to avoid

it, and lastly, how to correct it once it is encountered. We

must first understand the capabilities of the aircraft or even

better what it is not capable of doing. For example, if you

were flying a helicopter with a maximum gross weight of

5,200 lb, would you knowingly try to take on fuel, baggage

and passengers causing the weight to be 5,500 lb? A wise

professional pilot should not ever exceed the certificated

maximum gross weight or performance flight weight for any

aircraft. The manuals are written for safety and reliability.

The limitations and emergency procedures are stressed

because lapses in procedures or exceeding limitations can

result in aircraft damage or human fatalities. At the very least,

exceeding limitations will increase the costs of maintenance

and ownership of any aircraft and especially helicopters.

Overloaded parts may fail before their designed lifetime. There

are no extra parts in helicopters. The respect and discipline

pilots exercise in following flight manuals should also be

applied to understanding aerodynamic conditions. If flight

envelopes are exceeded, the end results can be catastrophic.

LTE is an aerodynamic condition and is the result of a control

margin deficiency in the tail rotor. It can affect all single-rotor

helicopters that utilize a tail rotor. The design of main and

tail rotor blades and the tail boom assembly can affect the

characteristics and susceptibility of LTE but will not nullify

the phenomenon entirely. Translational lift is obtained by

any amount of clean air through the main rotor disk. Chapter

2, Aerodynamics of Flight, discusses translational lift with

respect to the main rotor blade, explaining that the more

clean air there is going through the rotor disk, the more

efficient it becomes. The same holds true for the tail rotor.

As the tail rotor works in less turbulent air, it reaches a point

of translational thrust. At this point, the tail rotor becomes

aerodynamically efficient and the improved efficiency

produces more antitorque thrust. The pilot can determine

when the tail rotor has reached translational thrust. As more

antitorque thrust is produced, the nose of the helicopter

yaws to the left (opposite direction of the tail rotor thrust),

forcing the pilot to correct with right pedal application

(actually decreasing the left pedal). This, in turn, decreases

the AOA in the tail rotor blades. Pilots should be aware of the

characteristics of the helicopter they fly and be particularly

aware of the amount of tail rotor pedal typically required for

different flight conditions.

LTE is a condition that occurs when the flow of air through

a tail rotor is altered in some way, by altering the angle or

speed at which the air passes through the rotating blades of

the tail rotor disk. As discussed in the previous paragraph, an

effective tail rotor relies on a stable and relatively undisturbed

11-19

0°

30°

60°

90°

120°

150°

180°

210°

240°

270°

300°

330°

360°

315°

285°

Wind

Figure 11-9. Main rotor disk vortex interference.

0°

30°

60°

90°

120°

150°

180°

210°

240°

270°

300°

330°

360°

Wind

Figure 11-10. Weathercock stability.

airflow in order to provide a steady and constant antitorque

reaction. The pitch and AOA of the individual blades will

determine the thrust. A change to either of these alters the

amount of thrust generated. A pilot’s yaw pedal input causes

a thrust reaction from the tail rotor. Altering the amount of

thrust delivered for the same yaw input creates an imbalance.

Taking this imbalance to the extreme will result in the loss

of effective control in the yawing plane, and LTE will occur.

This alteration of tail rotor thrust can be affected by numerous

external factors. The main factors contributing to LTE are:

1. Airflow and downdraft generated by the main rotor

blades interfering with the airflow entering the tail

rotor assembly.

2. Main blade vortices developed at the main blade tips

entering the tail rotor disk.

3. Turbulence and other natural phenomena affecting the

airflow surrounding the tail rotor.

4. A high-power setting, hence large main rotor

pitch angle, induces considerable main rotor blade

downwash and hence more turbulence than when the

helicopter is in a low power condition.

5. A slow forward airspeed, typically at speeds where

translational lift and translational thrust are in the

process of change and airflow around the tail rotor

will vary in direction and speed.

6. The airflow relative to the helicopter;

a. Worst case—relative wind within ±15° of the

10 o’clock position, generating vortices that

can blow directly into the tail rotor. This is

dictated by the characteristics of the helicopters

aerodynamics of tailboom position, tail rotor size

and position relative to the main rotor and vertical

stabilizer, size and shape. [Figure 11-9]

b. Weathercock stability—tailwinds from 120° to

240° [Figure 11-10], such as left crosswinds,

causing high pilot workload.

c. Tail rotor vortex ring state (210° to

330°). [Figure 11-11] Winds within this region

will result in the development of the vortex ring

state of the tail rotor.

7. Combinations (a, b, c) of these factors in a particular

situation can easily require more antitorque than the

helicopter can generate and in a particular environment

LTE can be the result.

Certain flight activities lend themselves to being at higher

risk of LTE than others. For example, power line and pipeline

patrol sectors, low speed aerial filming/photography as well

as in the Police and Helicopter Emergency Medical Services

(EMS) environments can find themselves in low-and-slow

situations over geographical areas where the exact wind speed

and direction are hard to determine.

11-20

0°

30°

60°

90°

120°

150°

180°

210°

240°

270°

300°

330°

360°

Wind

Figure 11-11. Tail rotor vortex ring state.

Unfortunately, the aerodynamic conditions that a helicopter

is susceptible to are not explainable in black and white terms.

LTE is no exception. There are a number of contributing

factors, but what is more important in preventing LTE is to

note them, and then to associate them with situations that

should be avoided. Whenever possible, pilots should learn

to avoid the following combinations:

1. Low and slow flight outside of ground effect.

2. Winds from ±15º of the 10 o’clock position and

probably on around to 5 o’clock position [Figure 11-9]

3. Tailwinds that may alter the onset of translational lift

and translational thrust, and hence induce high power

demands and demand more anti-torque (left pedal)

than the tail rotor can produce.

4. Low speed downwind turns.

5. Large changes of power at low airspeeds.

6. Low speed flight in the proximity of physical

obstructions that may alter a smooth airflow to both

the main rotor and tail rotor.

Pilots who put themselves in situations where the combinations

above occur should know that they are likely to encounter

LTE. The key is not to put the helicopter in a compromising

condition, while at the same time being educated enough

to recognize the onset of LTE and being prepared to react

quickly to it before the helicopter cannot be controlled.

Early detection of LTE, followed by the immediate flight

control application of corrective action, applying forward

cyclic to regain airspeed, applying right pedal not left as

necessary to maintain rotor rpm, and reducing the collective

(thus reducing the high-power demand on the tail rotor), is the

key to a safe recovery. Pilots should always set themselves

up when conducting any maneuver to have enough height

and space available to recover in the event they encounter

an aerodynamic situation such as LTE.

Understanding the aerodynamic phenomenon of LTE is by

far the most important factor in preventing an LTE-related

accident, and maintaining the ability and option either to go

around if making an approach or pull out of a maneuver safely

and re-plan, is always the safest option. Having the ability to

fly away from a situation and re-think the possible options

should always be part of a pilot's planning process in all phases

of flight. Unfortunately, there have been many pilots who

have idled a good engine and fully functioning tail rotor disk

and autorotated a perfectly airworthy helicopter to the crash

site because they misunderstood or misperceived both the

limitations of the helicopter and the aerodynamic situation.

Main Rotor Disk Interference (285–315°)

Refer to Figure 11-9. Winds at velocities of 10–30 knots from

the left front cause the main rotor vortex to be blown into the

tail rotor by the relative wind. This main rotor disk vortex

causes the tail rotor to operate in an extremely turbulent

environment. During a right turn, the tail rotor experiences a

reduction of thrust as it comes into the area of the main rotor

disk vortex. The reduction in tail rotor thrust comes from the

airflow changes experienced at the tail rotor as the main rotor

disk vortex moves across the tail rotor disk.

The effect of the main rotor disk vortex initially increases the

AOA of the tail rotor blades, thus increasing tail rotor thrust.

The increase in the AOA requires that right pedal pressure

be added to reduce tail rotor thrust in order to maintain the

same rate of turn. As the main rotor vortex passes the tail

rotor, the tail rotor AOA is reduced. The reduction in the

AOA causes a reduction in thrust and right yaw acceleration

begins. This acceleration can be surprising, since previously

adding right pedal to maintain the right turn rate. This thrust

reduction occurs suddenly, and if uncorrected, develops

into an uncontrollable rapid rotation about the mast. When

operating within this region, be aware that the reduction in

tail rotor thrust can happen quite suddenly, and be prepared

to react quickly to counter this reduction with additional left

pedal input.

Weathercock Stability (120–240°)

In this region, the helicopter attempts to weathervane,

or weathercock, its nose into the relative wind.

[Figure 11-10] Unless a resisting pedal input is made, the

helicopter starts a slow, uncommanded turn either to the right

11-21

or left, depending upon the wind direction. If the pilot allows

a right yaw rate to develop and the tail of the helicopter moves

into this region, the yaw rate can accelerate rapidly. In order

to avoid the onset of LTE in this downwind condition, it is

imperative to maintain positive control of the yaw rate and

devote full attention to flying the helicopter.

Tail Rotor Vortex Ring State (210–330°)

Winds within this region cause a tail rotor vortex ring state to

develop. [Figure 11-11] The result is a nonuniform, unsteady

flow into the tail rotor. The vortex ring state causes tail

rotor thrust variations, which result in yaw deviations. The

net effect of the unsteady flow is an oscillation of tail rotor

thrust. Rapid and continuous pedal movements are necessary

to compensate for the rapid changes in tail rotor thrust when

hovering in a left crosswind. Maintaining a precise heading

in this region is difficult, but this characteristic presents

no significant problem unless corrective action is delayed.

However, high pedal workload, lack of concentration, and

overcontrolling can lead to LTE.

When the tail rotor thrust being generated is less than the

thrust required, the helicopter yaws to the right. When

hovering in left crosswinds, concentrate on smooth pedal

coordination and do not allow an uncommanded right yaw to

develop. If a right yaw rate is allowed to build, the helicopter

can rotate into the wind azimuth region where weathercock

stability then accelerates the right turn rate. Pilot workload

during a tail rotor vortex ring state is high. Do not allow a

right yaw rate to increase.

LTE at Altitude

At higher altitudes where the air is thinner, tail rotor thrust

and efficiency are reduced. Because of the high-density

altitude, powerplants may be much slower to respond to

power changes. When operating at high altitudes and high

gross weights, especially while hovering, the tail rotor thrust

may not be sufficient to maintain directional control, and

LTE can occur. In this case, the hovering ceiling is limited

by tail rotor thrust and not necessarily power available. In

these conditions, gross weights need to be reduced and/

or operations need to be limited to lower density altitudes.

This may not be noted as criteria on the performance charts.

Reducing the Onset of LTE

To help reduce the onset of LTE, follow these steps:

1. Maintain maximum power-on rotor rpm. If the main

rotor rpm is allowed to decrease, the antitorque thrust

available is decreased proportionally.

2. Avoid tailwinds below airspeeds of 30 knots. If loss

of translational lift occurs, it results in an increased

power demand and additional antitorque pressures.

3. Avoid OGE operations and high-power demand

situations below airspeeds of 30 knots at low altitudes.

4. Be especially aware of wind direction and velocity

when hovering in winds of about 8–12 knots. A loss

of translational lift results in an unexpected high power

demand and an increased antitorque requirement.

5. Be aware that if a considerable amount of left pedal

is being maintained, a sufficient amount of left pedal

may not be available to counteract an unanticipated

right yaw.

6. Be alert to changing wind conditions, which may be

experienced when flying along ridge lines and around

buildings.

7. Execute right turns slowly. This limits the effects of

rotating inertia, and decreases loading on the tailrotor

to control yawing.

Recovery Technique (Uncontrolled Right Yaw)

If a sudden unanticipated right yaw occurs, the following

recovery technique should be performed. Apply full left

pedal. Simultaneously, apply forward cyclic control to

increase speed. If altitude permits, reduce power. As recovery

is affected, adjust controls for normal forward flight. A

recovery path must always be planned, especially when

terminating to an OGE hover and executed immediately if

an uncommanded yaw is evident.

Collective pitch reduction aids in arresting the yaw rate but

may cause an excessive rate of descent. Any large, rapid

increase in collective to prevent ground or obstacle contact

may further increase the yaw rate and decrease rotor rpm.

The decision to reduce collective must be based on the pilot’s

assessment of the altitude available for recovery.

If the rotation cannot be stopped and ground contact is

imminent, an autorotation may be the best course of action.

Maintain full left pedal until the rotation stops, then adjust to

maintain heading. For more information on LTE, see Advisory

Circular (AC) 90-95, Unanticipated Right Yaw in Helicopters.

Main Drive Shaft or Clutch Failure

The main drive shaft, located between the engine and the main

rotor transmission, provides engine power to the main rotor

transmission. In some helicopters, particularly those with

piston engines, a drive belt is used instead of a drive shaft.

A failure of the drive shaft clutch or belt has the same effect

as an engine failure because power is no longer provided to

the main rotor and an autorotation must be initiated. There

are a few differences, however, that need to be taken into

11-22

consideration. If the drive shaft or belt breaks, the lack of any

load on the engine results in an overspeed. In this case, the

throttle must be closed in order to prevent any further damage.

In some helicopters, the tail rotor drive system continues to

be powered by the engine even if the main drive shaft breaks.

In this case, when the engine unloads, a tail rotor overspeed

can result. If this happens, close the throttle immediately and

enter an autorotation. The pilot must be knowledgeable of the

specific helicopter’s system and failure modes.

Pilots should keep in mind that when there is any suspected

mechanical malfunction, first and foremost they should

always attempt to maintain rotor rpm. If the rotor rpm is at the

normal indication with normal power settings, an instrument

failure might be occurring, and it would be best to fly the

helicopter to a safe landing area. If the rotor rpm is in fact

decreasing or low, then there is a drive line failure.

Hydraulic Failure

Many helicopters incorporate the use of hydraulic actuators to

overcome high control forces. A hydraulic system consists of

actuators, also called servos, on each flight control; a pump,

which is usually driven by the main rotor transmission;

and a reservoir to store the hydraulic fluid. A switch in the

cockpit can turn the system off, although it is left on during

normal conditions. A pressure indicator in the cockpit may

be installed to monitor the system.

An impending hydraulic failure can be recognized by a

grinding or howling noise from the pump or actuators,

increased control forces and feedback, and limited control

movement. The required corrective action is stated in detail

in the RFM. In most cases, airspeed needs to be reduced in

order to reduce control forces. The hydraulic switch and

circuit breaker should be checked and recycled. If hydraulic

power is not restored, make a shallow approach to a running

or roll-on landing. This technique is used because it requires

less control force and pilot workload. Additionally, the

hydraulic system should be disabled by placing the switch

in the off position. The reason for this is to prevent an

inadvertent restoration of hydraulic power, which may lead

to overcontrolling near the ground.

In those helicopters in which the control forces are so high

that they cannot be moved without hydraulic assistance, two

or more independent hydraulic systems are installed. Some

helicopters use hydraulic accumulators to store pressure that

can be used for a short time while in an emergency if the

hydraulic pump fails. This gives enough time to land the

helicopter with normal control.

Governor or Fuel Control Failure

Governors and fuel control units automatically adjust engine

power to maintain rotor rpm when the collective pitch

is changed. If the governor or fuel control unit fails, any

change in collective pitch requires manual adjustment of

the throttle to maintain correct rpm. In the event of a high

side failure, the engine and rotor rpm tend to increase above

the normal range due to the engine being commanded to

put out too much power. If the rpm cannot be reduced and

controlled with the throttle, close the throttle and enter an

autorotation. If the failure is on the low side, the engine

output is allowed to go below the collective and normal

rpm may not be attainable, even if the throttle is manually

controlled. In this case, the collective has to be lowered to

maintain rotor rpm. A running or roll-on landing may be

performed if the engine can maintain sufficient rotor rpm. If

there is insufficient power, enter an autorotation. As stated

previously in this chapter, before responding to any type of

mechanical failure, pilots should confirm that rotor rpm is

not responding to flight control inputs. If the rotor rpm can

be maintained in the green operating range, the failure is in

the instrument, and not mechanical.

Abnormal Vibration

With the many rotating parts found in helicopters, some

vibration is inherent. A pilot needs to understand the

cause and effect of helicopter vibrations because abnormal

vibrations cause premature component wear and may even

result in structural failure. With experience, a pilot learns

what vibrations are normal and those that are abnormal

and can then decide whether continued flight is safe or not.

Helicopter vibrations are categorized into low, medium, or

high frequency.

Low-Frequency Vibrations

Low-frequency vibrations (100–500 cycles per minute) usually

originate from the main rotor disk. The main rotor operational

range, depending on the helicopter, is usually between 320

and 500 rpm. A rotor blade that is out of track or balance will

cause a cycle to occur with every rotation. The vibration may

be felt through the controls, the airframe, or a combination

of both. The vibration may also have a definite direction

of push or thrust. It may be vertical, lateral, horizontal, or

even a combination of these. Normally, the direction of the

vibration can be determined by concentrating on the feel of

the vibration, which may push a pilot up and down, backwards

and forwards, or in the case of a blade being out of phase, from

side to side. The direction of the vibration and whether it is

felt in the controls or the airframe is important information for

the mechanic when he or she troubleshoots the source. Out-

of-track or out-of-balance main rotor blades, damaged blades,

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worn bearings, dampers out of adjustment, or worn parts are

possible causes of low frequency vibrations.

Medium- and High-Frequency Vibrations

Medium-frequency vibrations (1,000–2,000 cycles per

minute) range between the low frequencies of the main rotor

(100–500 cycles per minute) and the high frequencies (2,100

cycles per minute or higher) of the engine and tail rotor.

Depending on the helicopter, medium-frequency vibration

sources may be engine and transmission cooling fans, and

accessories such as air conditioner compressors, or driveline

components. Medium-frequency vibrations are felt through

the entire airframe, and prolonged exposure to the vibrations

will result in greater pilot fatigue.

Most tail rotor vibrations fall into the high-frequency range

(2,100 cycles per minute or higher) and can be felt through

the tail rotor pedals as long as there are no hydraulic actuators

to dampen out the vibration. This vibration is felt by the pilot

through his or her feet, which are usually “put to sleep” by

the vibration. The tail rotor operates at approximately a 6:1

ratio with the main rotor, meaning for every one rotation

of the main rotor the tail rotor rotates 6 times. A main

rotor operating rpm of 350 means the tail rotor rpm would

be 2,100 rpm. Any imbalance in the tail rotor disk is very

harmful as it can cause cracks to develop and rivets to work

loose. Piston engines usually produce a normal amount of

high-frequency vibration, which is aggravated by engine

malfunctions, such as spark plug fouling, incorrect magneto

timing, carburetor icing and/or incorrect fuel/air mixture.

Vibrations in turbine engines are often difficult to detect as

these engines operate at a very high rpm. Turbine engine

vibration can be at 30,000 rpm internally, but common

transmission speeds are in the 1,000 to 3,000 rpm range for

the output shaft. The vibrations in turbine engines may be

short lived as the engine disintegrates rapidly when damaged

due to high rpm and the forces present.

Tracking and Balance

Modern equipment used for tracking and balancing the main

and tail rotor blades can also be used to detect other vibrations

in the helicopter. These systems use accelerometers mounted

around the helicopter to detect the direction, frequency, and

intensity of the vibration. The built-in software can then

analyze the information, pinpoint the origin of the vibration,

and suggest the corrective action.

The use of a system such as a health and usage monitoring

system (HUMS) provides the operator the ability to record

engine and transmission performance and provide rotor track

and balance. This system has been around for over 30 years

and is now becoming more affordable, more capable, and

more commonplace in the rotorcraft industry.

Multiengine Emergency Operations

Single-Engine Failure

When one engine has failed, the helicopter can often maintain

altitude and airspeed until a suitable landing site can be

selected. Whether or not this is possible becomes a function

of such combined variables as aircraft weight, density

altitude, height above ground, airspeed, phase of flight,

and single-engine capability. Environmental response time

and control technique may be additional factors. Caution

must be exercised to correctly identify the malfunctioning

engine since there is no telltale yawing as occurs in most

multiengine airplanes. Shutting down the wrong engine

could be disastrous!

Even when flying multiengine powered helicopters, rotor rpm

must be maintained at all costs, because fuel contamination has

been documented as the cause for both engines failing in flight.

Dual-Engine Failure

The flight characteristics and the required crew member

control responses after a dual-engine failure are similar to

those during a normal power-on descent. Full control of the

helicopter can be maintained during autorotational descent.

In autorotation, as airspeed increases above 70–80 KIAS, the

rate of descent and glide distance increase significantly. As

airspeed decreases below approximately 60 KIAS, the rate

of descent increases and glide distance decreases.

Lost Procedures

Pilots become lost while flying for a variety of reasons, such

as disorientation, flying over unfamiliar territory, or visibility

that is low enough to render familiar terrain unfamiliar. When

a pilot becomes lost, the first order of business is to fly the

aircraft; the second is to implement lost procedures. Keep

in mind that the pilot workload will be high, and increased

concentration will be necessary. If lost, always remember to

look for the practically invisible hazards, such as wires, by

searching for their support structures, such as poles or towers,

which are almost always near roads.

If lost, follow common sense procedures.

• Try to locate any large landmarks, such as lakes, rivers,

towers, railroad tracks, or Interstate highways. If a

landmark is recognized, use it to find the helicopter’s

location on the sectional chart. If flying near a town or

city, a pilot may be able to read the name of the town

on a water tower or even land to ask for directions.

• If no town or city is nearby, the first thing a pilot should

do is climb. An increase in altitude increases radio and

navigation reception range as well as radar coverage.

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risk associated with being lost is waiting too long to land in a

safe area. Helicopter pilots should land before fuel exhaustion

occurs because maneuvering with low fuel levels could cause

the engine to stop due to fuel starvation as fuel sloshes or

flows away from the pickup port in the tank.

If lost and low on fuel, it is advisable to make a precautionary

landing. Preferably, land near a road or in an area that would

allow space for another helicopter to safely land and provide

assistance. Having fuel delivered is a minor inconvenience

when compared to having an accident. Once on the ground,

pilots may seek assistance.

VFR Flight into Instrument Meteorological

Conditions

Helicopters, unlike airplanes, generally operate under Visual

Flight Rules (VFR) and require pilots to maintain aircraft

control by visual cues. However, when unforecast weather

leads to degraded visibility, the pilot may be at increased

risk of Inadvertent flight into Instrument Meteorological

Conditions (IIMC). During an IIMC encounter, the pilot

may be unprepared for the loss of visual reference, resulting

in a reduced ability to continue safe flight. IIMC is a life-

threatening emergency for any pilot. To capture these IIMC

events, the Commercial Aviation Safety Team (CAST) and

International Civil Aviation Organization (ICAO) Common

Taxonomy Team (CICTT) categorizes this occurrence as

Unintended flight in Instrument Meteorological Conditions

(UIMC). This term is also recognized by the National

Transportation Safety Board (NTSB) and Federal Aviation

Administration (FAA). It is used to classify occurrences

(accidents and incidents) at a high level to improve the

capacity to focus on common safety issues and complete

analysis of the data in support of safety initiatives.

The onset of IIMC may occur gradually or suddenly, has

no simple procedural exit, and is unlike flight training by

reference to while in Visual Meteorological Conditions

(VMC). Most training helicopters are not equipped or

certified to fly under Instrument Flight Rules (IFR).

Therefore, General Aviation (GA) helicopter pilots may not

have the benefit of flight in actual Instrument Meteorological

Conditions (IMC) during their flight training. Helicopter

pilots that encounter IIMC may experience physiological

illusions which can lead to spatial disorientation and loss of

aircraft control. Even with some instrument training, many

available and accessible helicopters are not equipped with

the proper augmented safety systems or autopilots, which

would significantly aid in helicopter control during an

IIMC emergency. The need to use outside visual references

is natural for helicopter pilots because much of their flight

training is based upon visual cues, not on flight instruments.

This primacy can only be overcome through significant

instrument training. Additionally, instrument flight may be

• Navigation aids, dead reckoning, and pilotage are

skills that can be used as well.

• Do not forget air traffic control (ATC)—controllers

assist pilots in many ways, including finding a lost

helicopter. Once communication with ATC has been

established, follow their instructions.

These common-sense procedures can be easily remembered by

using the four Cs: Climb, Communicate, Confess, and Comply.

• Climb for a better view, improved communication and

navigation reception, and terrain avoidance.

• Communicate by calling the nearest flight service

station (FSS)/automated flight service station (AFSS)

on 122.2 MHz. If the FSS/AFSS does not respond,

call the nearest control tower, center, or approach

control. For frequencies, check the chart in the vicinity

of the last known position. If that fails, switch to

the emergency radio frequency (121.5 MHz) and

transponder code (7700).

• Report the lost situation to ATC and request help.

• Comply with controller instructions.

Pilots should understand the services provided by ATC and

the resources and options available. These services enable

pilots to focus on aircraft control and help them make better

decisions in a time of stress.

When contacting ATC, pilots should provide as much

information as possible because ATC uses the information

to determine what kind of assistance it can provide with

available assets and capabilities. Information requirements

vary depending on the existing situation, but at a minimum

a pilot should provide the following information:

• Aircraft identification and type

• Nature of the emergency

• Aviator’s desires

To reduce the chances of getting lost in the first place, use

flight following through active contact with an aircraft during

flight either by radio or through automated flight following

systems when it is available, monitor checkpoints no more

than 25 miles apart, keep navigation aids such as Very

High-Frequency Omni-Directional Range (VOR) tuned in,

and maintain good situational awareness. Flight following

provides ongoing surveillance information to assist pilots in

avoiding collisions with other aircraft.

Getting lost is a potentially dangerous situation for any

aircraft, especially when low on fuel. Due to the helicopter’s

unique ability to land almost anywhere, pilots have more

flexibility than other aircraft as to landing site. An inherent

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intimidating to some and too costly for others. As a result,

many helicopter pilots choose not to seek an instrument

rating.

While commercial helicopter operators often prefer their

pilots to be instrument rated, fatal accidents still occur as

a result of IIMC. Many accidents can be traced back to

the pilot’s inability to recover the helicopter after IIMC

is encountered, even with adequate equipment installed.

Therefore, whether instrument rated or not, all pilots should

understand that avoiding IIMC is critical.

A good practice for any flight is to set and use personal

minimums, which should be more conservative than those

required by regulations for VFR flight. In addition, a thorough

preflight and understanding of weather conditions that may

contribute to the risk of IMC developing along a planned

route of flight is essential for safety. Pilots should recognize

deteriorating weather conditions so the route of flight can be

changed or a decision made to terminate the flight and safely

land at a suitable area, well before IIMC occurs. If weather

conditions deteriorate below the pilot’s personal minimums

during flight, a pilot who understands the risks of IIMC

knows that he or she is at an en route decision point, where

it is necessary to either turn back to the departure point or

immediately land somewhere safe to wait until the weather

has cleared. Pilots should recognize that descent below a

predetermined minimum altitude above ground level (AGL)

(for example, 500 feet AGL) to avoid clouds or, slowing

the helicopter to a predetermined minimum airspeed (for

example, slowing to 50 KIAS) to reduce the rate of closure

from the deteriorating weather conditions, indicates the

decision point had been reached. Ceilings that are lower than

reported and/or deteriorating visibility along the route of

flight should trigger the decision to discontinue and amend

the current route to avoid IIMC.

If the helicopter pilot is instrument rated, it is advisable to

maintain instrument currency and proficiency as this may

aid the pilot in a safe recovery from IIMC. A consideration

for instrument rated pilots when planning a VFR flight

should include a review of published instrument charts for

safe operating altitudes, e.g. minimum safe altitude (MSA),

minimum obstruction clearance altitude (MOCA), minimum

in VMC throughout a flight: off-route altitude (MORA),

etc. If IIMC occurs, the pilot may consider a climb to a safe

altitude. Once the helicopter is stabilized, the pilot should

declare an emergency with air traffic control (ATC). It is

imperative that the pilot commit to controlling the helicopter

and remember to aviate, navigate, and finally communicate.

Often communication is attempted first, as it is natural to

look for help in stressful situations. This may distract the

pilot from maintaining control of the helicopter.

If the pilot is not instrument rated, instrument current nor

proficient, or is flying a non-IFR equipped helicopter,

remaining in VMC is paramount. Pilots who are not trained

or proficient in flight solely by reference to instruments have

a tendency to attempt to maintain flight by visual ground

reference, which tends to result in flying at lower altitudes,

just above the trees or by following roads. The thought process

is that, "as long as I can see what is below me, I can continue

to my intended destination." Experience and statistical data

indicate that attempting to continue VFR flight into IMC can

often lead to a fatal outcome as pilots often fixate on what

they see below them and are unable to see the hazards ahead

of them (e.g., power lines, towers, rising terrain, etc.). By

the time the pilot sees the hazard, it is either too late to avoid

a collision, or while successfully maneuvering to avoid an

obstacle, the pilot becomes disoriented.

Flying at night involves even more conservative personal

minimums to ensure safety and avoidance of IIMC than

daytime flying. At night, deteriorating weather conditions

may be difficult to detect. Therefore, pilots should ensure

that they not only receive a thorough weather briefing, but

that they remain vigilant for unforecasted weather during

their flight. The planned route should include preselected

landing sites that will provide options to the pilot in the

event a precautionary landing is required to avoid adverse

weather conditions. As a pilot gains night flight experience

their ability to assess weather during a flight will improve.

Below are some basic guidelines to assist a pilot to remain

in VMC throughout a flight:

1. Slowly turn around if threatened by deteriorating

visual cues and proceed back to VMC or to the first

safe landing area if the weather ahead becomes

questionable. Remember that prevention is paramount.

2. Do not proceed further on a course when the terrain

ahead is not clearly discernible.

3. Delay or consider cancelling the flight if weather

conditions are already questionable, could deteriorate

significantly based on forecasts, or if you are uncertain

whether the flight can be conducted safely. Often, a

gut feeling can provide a warning that unreasonable

risks are present.

4. Always have a safe landing area (such as large open

areas or airports) in mind for every route of flight.

There are five basic steps that every pilot should be familiar

with, and which should be executed immediately at the onset

of IIMC, if applicable. However, remember that if you are

not trained to execute the following maneuvers solely by

reference to instruments, or your aircraft is not equipped

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Food cannot be subject to deterioration due to heat or cold. There

should be at least 10,000 calories for each person on board, and it

should be stored in a sealed waterproof container. It should have

been inspected within the previous 6 months, verifying the amount

and satisfactory condition of the contents.

A supply of water

Cooking utensils

Matches in a waterproof container

A portable compass

An ax weighing at least 2.5 pounds with a handle not less than 28 inches

in length

A flexible saw blade or equivalent cutting tool

30 feet of snare wire and instructions for use

Fishing equipment, including still-fishing bait and gill net with not more

than a two-inch mesh

Mosquito nets or netting and insect repellent sufficient to meet the

needs of all persons aboard, when operating in areas where insects

are likely to be hazardous

A signaling mirror

At least three pyrotechnic distress signals

A sharp, quality jackknife or hunting knife

A suitable survival instruction manual

Flashlight with spare bulbs and batteries

Portable emergency locator transmitter (ELT) with spare batteries

Stove with fuel or a self-contained means of providing heat for cooking

Tent(s) to accommodate everyone on board

Additional items for winter operations:

• Winter sleeping bags for all persons when the

temperature is expected to be below 7 °C

• Two pairs of snow shoes

• Spare ax handle

• Ice chisel

• Snow knife or saw knife

EMERGENCY EQUIPMENT AND SURVIVAL GEAR

Figure 11-12. Emergency equipment and survival gear.

with such instruments, this guidance may be less beneficial

to you and loss of helicopter control may occur:

1. Level the “wings” – level the bank angle using the

attitude indicator.

2. Attitude – set a climb attitude that achieves a safe

climb speed appropriate to your type of helicopter.

This is often no more than 10° of pitch up on the

attitude indicator.

3. Airspeed – verify that the attitude selected has

achieved the desired airspeed. It is critical to

recognize that slower airspeeds, closer to effective

translational lift, may require large control inputs and

will decrease stability, making recover impossible

while in UIMC.

4. Power – adjust to a climb power setting relative to the

desired airspeed. This should be executed concurrent

with steps 2 and 3.

5. Heading and Trim – pick a heading known to be free

of obstacles and maintain it. This will likely be the

heading you were already on, which was planned and

briefed. Set the heading bug, if installed, to avoid over-

controlling your bank. Maintain coordinated flight so

that an unusual attitude will not develop.

Try to avoid immediately turning 180°. Turning around is

not always the safest route and executing a turn immediately

after UIMC may lead to spatial disorientation. If a 180° turn

is the safest option, first note the heading you are on then

begin the turn to the reciprocal heading, but only after stable

flight is achieved (items 1 through 5 above) and maintain

a constant rate of turn appropriate to the selected airspeed.

Each encounter with UIMC is unique, and no single

procedure can ensure a safe outcome. Considerations in

determining the best course of action upon encountering

UIMC should include, at a minimum, terrain, obstructions,

freezing levels, aircraft performance and limitations, and

availability of ATC services.

There are new technologies being developed regarding

aircraft design, enhanced and lower-cost technologies,

and aircraft certification. Because of this promising future,

much of the discussion and guidance in this chapter may

one day become irrelevant. As helicopters integrate more

into the National Airspace System, the IFR infrastructure

and instrument training will become more prevalent. In the

future, UIMC may no longer be the emergency that ends

with a fatality but rather associated with proper prevention,

skilled recovery techniques along with the aid of emerging

new life saving avionics technology. A helicopter instrument

rating may be a life-saving addition to a pilot’s level of

certification. Please refer to the Instrument Flying Handbook

(FAA-H-8083-15, as revised); Advanced Avionics Handbook

(FAA-H-8083-6, as revised); and the Pilot’s Handbook of

Aeronautical Knowledge (FAA-H-8083-25, as revised) for

further exploration of IFR operations and how to obtain an

instrument rating.

When faced with deteriorating weather, planning and

prevention, not recovery, are the best strategies to eliminate

UIMC-related accidents and fatalities.

11-27

Emergency Equipment and Survival Gear

Both Canada and Alaska require pilots to carry survival

gear. Always carry survival gear when flying over rugged

and desolate terrain. The items suggested in Figure 11-12

are both weather and terrain dependent. The pilot also needs

to consider how much storage space the helicopter has and

how the equipment being carried affects the overall weight

and balance of the helicopter.

Chapter Summary

Emergencies should always be anticipated. Knowledge

of the helicopter, possible malfunctions and failures, and

methods of recovery can help the pilot avoid accidents and

be a safer pilot. Helicopter pilots should always expect the

worse hazards and possible aerodynamic effects and plan for

a safe exit path or procedure to compensate for the hazard.