直升机飞行手册Rotorcraft flying handbook

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center. To center the ball, level the helicopter laterally

by reference to the other bank instruments, then center

the ball with pedal trim. Torque correction pressures

vary as you make power changes. Always check the

ball following such changes.

COMMON ERRORS DURING STRAIGHT-AND-

LEVEL FLIGHT

1. Failure to maintain altitude.

2. Failure to maintain heading.

3. Overcontrolling pitch and bank during corrections.

4. Failure to maintain proper pedal trim.

5. Failure to cross-check all available instruments.

30°

0°

60°

90°

Figure 12-14. The banking scale at the top of the attitude indicator indicates varying degrees of bank. In this example, the

helicopter is banked a little over 10° to the right.

12-11

POWER CONTROL DURING STRAIGHT-AND-

LEVEL FLIGHT

Establishing specific power settings is accomplished

through collective pitch adjustments and throttle

control, where necessary. For reciprocating powered

helicopters, power indications are observed on the

manifold pressure gauge. For turbine powered helicopters, power is observed on the torque gauge. (Since most

IFR certified helicopters are turbine powered, this

discussion concentrates on this type of helicopter.)

At any given airspeed, a specific power setting determines whether the helicopter is in level flight, in a

climb, or in a descent. For example, cruising airspeed

maintained with cruising power results in level flight.

If you increase the power setting and hold the airspeed

constant, the helicopter climbs. Conversely, if you

decrease power and hold the airspeed constant, the helicopter descends. As a rule of thumb, in a turbine-engine

powered helicopter, a 10 to 15 percent change in the

torque value required to maintain level flight results in a

climb or descent of approximately 500 f.p.m., if the airspeed remains the same.

If the altitude is held constant, power determines the

airspeed. For example, at a constant altitude, cruising

power results in cruising airspeed. Any deviation from

the cruising power setting results in a change of airspeed. When power is added to increase airspeed, the

nose of the helicopter pitches up and yaws to the right

in a helicopter with a counterclockwise main rotor

blade rotation. When power is reduced to decrease airspeed, the nose pitches down and yaws to the left. The

yawing effect is most pronounced in single-rotor helicopters, and is absent in helicopters with counter-rotating

rotors. To counteract the yawing tendency of the helicopter, apply pedal trim during power changes.

To maintain a constant altitude and airspeed in level

flight, coordinate pitch attitude and power control. The

relationship between altitude and airspeed determines

the need for a change in power and/or pitch attitude. If

the altitude is constant and the airspeed is high or low,

change the power to obtain the desired airspeed.

During the change in power, make an accurate interpretation of the altimeter; then counteract any deviation from the desired altitude by an appropriate change

of pitch attitude. If the altitude is low and the airspeed

is high, or vice versa, a change in pitch attitude alone

may return the helicopter to the proper altitude and airspeed. If both airspeed and altitude are low, or if both

are high, a change in both power and pitch attitude is

necessary.

To make power control easy when changing airspeed, it

is necessary to know the approximate power settings for

the various airspeeds that will be flown. When the air-

speed is to be changed any appreciable amount, adjust

the torque so that it is approximately five percent over or

under that setting necessary to maintain the new airspeed.

As the power approaches the desired setting, include the

torque meter in the cross-check to determine when the

proper adjustment has been accomplished. As the airspeed is changing, adjust the pitch attitude to maintain a

constant altitude. A constant heading should be maintained throughout the change. As the desired airspeed is

approached, adjust power to the new cruising power setting and further adjust pitch attitude to maintain altitude.

Overpowering and underpowering torque approximately

five percent results in a change of airspeed at a moderate

rate, which allows ample time to adjust pitch and bank

smoothly. The instrument indications for straight-andlevel flight at normal cruise, and during the transition

from normal cruise to slow cruise are illustrated in figures 12-15 and 12-16 on the next page. After the airspeed

has stabilized at slow cruise, the attitude indicator shows

an approximate level pitch attitude.

The altimeter is the primary pitch instrument during

level flight, whether flying at a constant airspeed, or

during a change in airspeed. Altitude should not change

during airspeed transitions. The heading indicator

remains the primary bank instrument. Whenever the

airspeed is changed any appreciable amount, the torque

meter is momentarily the primary instrument for power

control. When the airspeed approaches that desired, the

airspeed indicator again becomes the primary instrument for power control.

The cross-check of the pitch and bank instruments to

produce straight-and-level flight should be combined

with the power control instruments. With a constant

power setting, a normal cross-check should be

satisfactory. When changing power, the speed of the

cross-check must be increased to cover the pitch and

bank instruments adequately. This is necessary to

counteract any deviations immediately.

COMMON ERRORS DURING AIRSPEED CHANGES

1. Improper use of power.

2. Overcontrolling pitch attitude.

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instrument indicating a slight climb or descent even

when the helicopter is in level flight. If it cannot be

readjusted properly, this error must be taken into consideration when using the vertical speed indicator for

pitch control. For example, if the vertical speed indicator showed a descent of 100 f.p.m. when the helicopter

was in level flight, you would have to use that indication as level flight. Any deviation from that reading

would indicate a change in attitude.

AIRSPEED INDICATOR

The airspeed indicator gives an indirect indication of

helicopter pitch attitude. With a given power setting

and pitch attitude, the airspeed remains constant. If the

airspeed increases, the nose is too low and should be

raised. If the airspeed decreases, the nose is too high

and should be lowered. A rapid change in airspeed indicates a large change in pitch attitude, and a slow change

in airspeed indicates a small change in pitch attitude.

There is very little lag in the indications of the airspeed

indicator. If, while making attitude changes, you notice

some lag between control application and change of

airspeed, it is most likely due to cyclic control lag.

Generally, a departure from the desired airspeed, due to

an inadvertent pitch attitude change, also results in a

change in altitude. For example, an increase in airspeed

due to a low pitch attitude results in a decrease in altitude. A correction in the pitch attitude regains both airspeed and altitude.

BANK CONTROL

The bank attitude of a helicopter is the angular relation

of its lateral axis and the natural horizon. To maintain a

straight course in visual flight, you must keep the

lateral axis of the helicopter level with the natural horizon. Assuming the helicopter is in coordinated flight,

any deviation from a laterally level attitude produces a

turn. [Figure 12-13]

ATTITUDE INDICATOR

The attitude indicator gives a direct indication of the

bank attitude of the helicopter. For instrument flight,

BANK CONTR CONTROL OL

BANK CONTROL

Figure 12-13. The flight instruments used for bank control are the attitude, heading, and turn indicators.

12-10

the miniature aircraft and the horizon bar of the attitude

indicator are substituted for the actual helicopter and

the natural horizon. Any change in bank attitude of the

helicopter is indicated instantly by the miniature aircraft. For proper interpretations of this instrument, you

should imagine being in the miniature aircraft. If the

helicopter is properly trimmed and the rotor tilts, a turn

begins. The turn can be stopped by leveling the miniature

aircraft with the horizon bar. The ball in the turn-and-slip

indicator should always be kept centered through proper

pedal trim.

The angle of bank is indicated by the pointer on the

banking scale at the top of the instrument. [Figure 12-

14] Small bank angles, which may not be seen by

observing the miniature aircraft, can easily be determined by referring to the banking scale pointer.

Pitch and bank attitudes can be determined simultaneously on the attitude indicator. Even though the miniature

aircraft is not level with the horizon bar, pitch attitude can

be established by observing the relative position of the

miniature aircraft and the horizon bar.

The attitude indicator may show small misrepresentations of bank attitude during maneuvers that involve

turns. This precession error can be immediately

detected by closely cross-checking the other bank

instruments during these maneuvers. Precession normally is noticed when rolling out of a turn. If, on the

completion of a turn, the miniature aircraft is level and

the helicopter is still turning, make a small change of

bank attitude to center the turn needle and stop the

movement of the heading indicator.

HEADING INDICATOR

In coordinated flight, the heading indicator gives an

indirect indication of the helicopter’s bank attitude.

When a helicopter is banked, it turns. When the lateral

axis of the helicopter is level, it flies straight.

Therefore, in coordinated flight, when the heading indicator shows a constant heading, the helicopter is level

laterally. A deviation from the desired heading indicates a bank in the direction the helicopter is turning.

A small angle of bank is indicated by a slow change of

heading; a large angle of bank is indicated by a rapid

change of heading. If a turn is noticed, apply opposite

cyclic until the heading indicator indicates the desired

heading, simultaneously checking that the ball is centered. When making the correction to the desired heading, you should not use a bank angle greater than that

required to achieve a standard rate turn. In addition, if

the number of degrees of change is small, limit the

bank angle to the number of degrees to be turned. Bank

angles greater than these require more skill and precision in attaining the desired results. During straightand-level flight, the heading indicator is the primary

reference for bank control.

TURN INDICATOR

During coordinated flight, the needle of the turn-andslip indicator gives an indirect indication of the bank

attitude of the helicopter. When the needle is displaced from the vertical position, the helicopter is

turning in the direction of the displacement. Thus, if

the needle is displaced to the left, the helicopter is

turning left. Bringing the needle back to the vertical

position with the cyclic produces straight flight. A

close observation of the needle is necessary to accurately interpret small deviations from the desired

position.

Cross-check the ball of the turn-and-slip indicator to

determine that the helicopter is in coordinated flight. If

the rotor is laterally level and torque is properly compensated for by pedal pressure, the ball remains in the

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ATTITUDE INDICATOR

The attitude indicator gives a direct indication of the

pitch attitude of the helicopter. In visual flight, you

attain the desired pitch attitude by using the cyclic to

raise and lower the nose of the helicopter in relation to

the natural horizon. During instrument flight, you follow exactly the same procedure in raising or lowering

the miniature aircraft in relation to the horizon bar.

You may note some delay between control application

and resultant instrument change. This is the normal

control lag in the helicopter and should not be confused

with instrument lag. The attitude indicator may show

small misrepresentations of pitch attitude during

maneuvers involving acceleration, deceleration, or

turns. This precession error can be detected quickly by

cross-checking the other pitch instruments.

If the miniature aircraft is properly adjusted on the

ground, it may not require readjustment in flight. If the

miniature aircraft is not on the horizon bar after leveloff at normal cruising airspeed, adjust it as necessary

while maintaining level flight with the other pitch

instruments. Once the miniature aircraft has been

adjusted in level flight at normal cruising airspeed,

leave it unchanged so it will give an accurate picture of

pitch attitude at all times.

When making initial pitch attitude corrections to maintain altitude, the changes of attitude should be small

and smoothly applied. The initial movement of the

horizon bar should not exceed one bar width high or

low. [Figure 12-12] If a further change is required, an

additional correction of one-half bar normally corrects

any deviation from the desired altitude. This one and

one-half bar correction is normally the maximum pitch

attitude correction from level flight attitude. After you

have made the correction, cross-check the other pitch

instruments to determine whether the pitch attitude

change is sufficient. If more correction is needed to

return to altitude, or if the airspeed varies more than 10

knots from that desired, adjust the power.

ALTIMETER

The altimeter gives an indirect indication of the pitch

attitude of the helicopter in straight-and-level flight.

Since the altitude should remain constant in level

flight, deviation from the desired altitude shows a need

for a change in pitch attitude, and if necessary, power.

When losing altitude, raise the pitch attitude and, if

necessary, add power. When gaining altitude, lower the

pitch attitude and, if necessary, reduce power.

The rate at which the altimeter moves helps in determining pitch attitude. A very slow movement of the

altimeter indicates a small deviation from the desired

pitch attitude, while a fast movement of the altimeter

indicates a large deviation from the desired pitch attitude. Make any corrective action promptly, with small

control changes. Also, remember that movement of the

altimeter should always be corrected by two distinct

changes. The first is a change of attitude to stop the

altimeter; and the second, a change of attitude to

return smoothly to the desired altitude. If the altitude

and airspeed are more than 100 feet and 10 knots low,

respectively, apply power along with an increase of

pitch attitude. If the altitude and airspeed are high by

more than 100 feet and 10 knots, reduce power and

lower the pitch attitude.

There is a small lag in the movement of the altimeter;

however, for all practical purposes, consider that the

altimeter gives an immediate indication of a change, or

a need for change in pitch attitude.

Since the altimeter provides the most pertinent information regarding pitch in level flight, it is considered

primary for pitch.

VERTICAL SPEED INDICATOR

The vertical speed indicator gives an indirect indication

of the pitch attitude of the helicopter and should be used

in conjunction with the other pitch instruments to attain

a high degree of accuracy and precision. The instrument

indicates zero when in level flight. Any movement of

the needle from the zero position shows a need for an

immediate change in pitch attitude to return it to zero.

Always use the vertical speed indicator in conjunction

with the altimeter in level flight. If a movement of the

vertical speed indicator is detected, immediately use the

proper corrective measures to return it to zero. If the

correction is made promptly, there is usually little or no

change in altitude. If you do not zero the needle of the

Figure 12-12. The initial pitch correction at normal cruise is

one bar width.

12-9

vertical speed indicator immediately, the results will

show on the altimeter as a gain or loss of altitude.

The initial movement of the vertical speed needle is

instantaneous and indicates the trend of the vertical

movement of the helicopter. It must be realized that

a period of time is necessary for the vertical speed

indicator to reach its maximum point of deflection

after a correction has been made. This time element

is commonly referred to as “lag.” The lag is directly

proportional to the speed and magnitude of the pitch

change. If you employ smooth control techniques

and make small adjustments in pitch attitude, lag is

minimized, and the vertical speed indicator is easy

to interpret. Overcontrolling can be minimized by

first neutralizing the controls and allowing the pitch

attitude to stabilize; then readjusting the pitch attitude by noting the indications of the other pitch

instruments.

Occasionally, the vertical speed indicator may be

slightly out of calibration. This could result in the

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you will encounter a problem called “fixation.” This results

from a natural human inclination to observe a specific

instrument carefully and accurately, often to the exclusion

of other instruments. Fixation on a single instrument usually results in poor control. For example, while performing

a turn, you may have a tendency to watch only the turn-andslip indicator instead of including other instruments in your

cross-check. This fixation on the turn-and-slip indicator

often leads to a loss of altitude through poor pitch and bank

control. You should look at each instrument only long

enough to understand the information it presents, then continue on to the next one. Similarly, you may find yourself

placing too much “emphasis” on a single instrument,

instead of relying on a combination of instruments nec-

essary for helicopter performance information. This differs from fixation in that you are using other instruments,

but are giving too much attention to a particular one.

During performance of a maneuver, you may sometimes

fail to anticipate significant instrument indications following attitude changes. For example, during leveloff

from a climb or descent, you may concentrate on pitch

control, while forgetting about heading or roll information. This error, called “omission,” results in erratic

control of heading and bank.

In spite of these common errors, most pilots can adapt

well to flight by instrument reference after instruction

and practice. You may find that you can control the helicopter more easily and precisely by instruments.

INSTRUMENT INTERPRETATION

The flight instruments together give a picture of what

is going on. No one instrument is more important than

the next; however, during certain maneuvers or conditions, those instruments that provide the most pertinent

and useful information are termed primary instruments.

Those which back up and supplement the primary

instruments are termed supporting instruments. For

example, since the attitude indicator is the only instrument that provides instant and direct aircraft attitude

information, it should be considered primary during

any change in pitch or bank attitude. After the new attitude is established, other instruments become primary,

and the attitude indicator usually becomes the supporting instrument.

Figure 12-10. In most situations, the cross-check pattern includes the attitude indicator between the cross-check of each of the

other instruments. A typical cross-check might progress as follows: attitude indicator, altimeter, attitude indicator, VSI, attitude

indicator, heading indicator, attitude indicator, and so on.

12-7

AIRCRAFT CONTROL

Controlling the helicopter is the result of accurately

interpreting the flight instruments and translating these

readings into correct control responses. Aircraft control

involves adjustment to pitch, bank, power, and trim in

order to achieve a desired flight path.

Pitch attitude control is controlling the movement of

the helicopter about its lateral axis. After interpreting

the helicopter’s pitch attitude by reference to the pitch

instruments (attitude indicator, altimeter, airspeed indicator, and vertical speed indicator), cyclic control

adjustments are made to affect the desired pitch attitude. In this chapter, the pitch attitudes illustrated are

approximate and will vary with different helicopters.

Bank attitude control is controlling the angle made by

the lateral tilt of the rotor and the natural horizon, or,

the movement of the helicopter about its longitudinal

axis. After interpreting the helicopter’s bank instruments (attitude indicator, heading indicator, and turn

indicator), cyclic control adjustments are made to attain

the desired bank attitude.

Power control is the application of collective pitch with

corresponding throttle control, where applicable. In

straight-and-level flight, changes of collective pitch are

made to correct for altitude deviations if the error is

more than 100 feet, or the airspeed is off by more than

10 knots. If the error is less than that amount, use a

slight cyclic climb or descent.

In order to fly a helicopter by reference to the

instruments, you should know the approximate

power settings required for your particular helicopter

in various load configurations and flight conditions.

Trim, in helicopters, refers to the use of the cyclic centering button, if the helicopter is so equipped, to relieve all

possible cyclic pressures. Trim also refers to the use of

pedal adjustment to center the ball of the turn indicator.

Pedal trim is required during all power changes.

The proper adjustment of collective pitch and cyclic

friction helps you relax during instrument flight.

Friction should be adjusted to minimize overcontrolling and to prevent creeping, but not applied to such a

degree that control movement is limited. In addition,

many helicopters equipped for instrument flight contain stability augmentation systems or an autopilot to

help relieve pilot workload.

STRAIGHT-AND-LEVEL FLIGHT

Straight-and-level unaccelerated flight consists of

maintaining the desired altitude, heading, airspeed, and

pedal trim.

PITCH CONTROL

The pitch attitude of a helicopter is the angular relation

of its longitudinal axis and the natural horizon. If available, the attitude indicator is used to establish the

desired pitch attitude. In level flight, pitch attitude

varies with airspeed and center of gravity. At a constant

altitude and a stabilized airspeed, the pitch attitude is

approximately level. [Figure 12-11]

PITCH CONTR CONTROL OL

PITCH CONTROL

Figure 12-11. The flight instruments for pitch control are the airspeed indicator, attitude indicator, altimeter, and vertical

speed indicator.

12-8

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Besides the magnetic fields generated by the earth, other

magnetic fields are produced by metal and electrical

accessories within the helicopter. These magnetic fields

distort the earth’s magnet force and cause the compass

to swing away from the correct heading. Manufacturers

often install compensating magnets within the compass

housing to reduce the effects of deviation. These magnets are usually adjusted while the engine is running and

all electrical equipment is operating. Deviation error,

however, cannot be completely eliminated; therefore, a

compass correction card is mounted near the compass.

The compass correction card corrects for deviation that

occurs from one heading to the next as the lines of force

interact at different angles.

MAGNETIC DIP

Magnetic dip is the result of the vertical component of

the earth’s magnetic field. This dip is virtually nonexistent at the magnetic equator, since the lines of force

are parallel to the earth’s surface and the vertical component is minimal. As you move a compass toward the

poles, the vertical component increases, and magnetic

dip becomes more apparent at these higher latitudes.

Magnetic dip is responsible for compass errors during

acceleration, deceleration, and turns.

Acceleration and deceleration errors are fluctuations

in the compass during changes in speed. In the northern hemisphere, the compass swings toward the north

during acceleration and toward the south during deceleration. When the speed stabilizes, the compass

returns to an accurate indication. This error is most

pronounced when you are flying on a heading of east

or west, and decreases gradually as you fly closer to a

north or south heading. The error does not occur when

you are flying directly north or south. The memory

aid, ANDS (Accelerate North, Decelerate South) may

help you recall this error. In the southern hemisphere,

this error occurs in the opposite direction.

Turning errors are most apparent when you are turning

to or from a heading of north or south. This error

increases as you near the poles as magnetic dip becomes

more apparent. There is no turning error when flying

near the magnetic equator. In the northern hemisphere,

when you make a turn from a northerly heading, the

compass gives an initial indication of a turn in the

opposite direction. It then begins to show the turn in

the proper direction, but lags behind the actual heading. The amount of lag decreases as the turn continues,

then disappears as the helicopter reaches a heading of

east or west. When you make a turn from a southerly

heading, the compass gives an indication of a turn in

the correct direction, but leads the actual heading. This

error also disappears as the helicopter approaches an

east or west heading.

INSTRUMENT CHECK—Prior to flight, make sure that

the compass is full of fluid. During hover turns, the

compass should swing freely and indicate known headings. Since that magnetic compass is required for all

flight operations, the aircraft should never be flown

with a faulty compass.

INSTRUMENT FLIGHT

To achieve smooth, positive control of the helicopter

during instrument flight, you need to develop three

fundamental skills. They are instrument cross-check,

instrument interpretation, and aircraft control.

INSTRUMENT CROSS-CHECK

Cross-checking, sometimes referred to as scanning, is

the continuous and logical observation of instruments

for attitude and performance information. In attitude

instrument flying, an attitude is maintained by reference

to the instruments, which produces the desired result in

performance. Due to human error, instrument error, and

helicopter performance differences in various atmospheric and loading conditions, it is difficult to

establish an attitude and have performance remain

constant for a long period of time. These variables make

A

True

North Pole

Magnetic

North Pole

Agonic

Line

20°

20°

15°

15°

10° 5°

5°

0°

Isogonic Lines

17°

10°

Figure 12-9. Variation at point A in the western United States

is 17°. Since the magnetic north pole is located to the east of

the true north pole in relation to this point, the variation is

easterly. When the magnetic pole falls to the west of the true

north pole, variation is westerly.

12-6

it necessary for you to constantly check the instruments

and make appropriate changes in the helicopter’s attitude. The actual technique may vary depending on what

instruments are installed and where they are installed,

as well as your experience and proficiency level. For

this discussion, we will concentrate on the six basic

flight instruments discussed earlier. [Figure 12-10]

At first, you may have a tendency to cross-check

rapidly, looking directly at the instruments without

knowing exactly what information you are seeking.

However, with familiarity and practice, the instrument

cross-check reveals definite trends during specific

flight conditions. These trends help you control the

helicopter as it makes a transition from one flight

condition to another.

If you apply your full concentration to a single instrument,

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Drive Gear

Compass

Card Gear

Figure 12-6. A heading indicator displays headings based on

a 360° azimuth, with the final zero omitted. For example, a 6

represents 060°, while a 21 indicates 210°. The adjustment

knob is used to align the heading indicator with the magnetic

compass.

12-4

Due to internal friction within the gyroscope, precession is common in heading indicators. Precession

causes the selected heading to drift from the set value.

Some heading indicators receive a magnetic north reference from a remote source and generally need no

adjustment. Heading indicators that do not have this

automatic north-seeking capability are often called

“free” gyros, and require that you periodically adjust

them. You should align the heading indicator with the

magnetic compass before flight and check it at 15-

minute intervals during flight. When you do an in-flight

alignment, be certain you are in straight-and-level,

unaccelerated flight, with the magnetic compass showing a steady indication.

TURN INDICATORS

Turn indicators show the direction and the rate of turn.

A standard rate turn is 3° per second, and at this rate

you will complete a 360° turn in two minutes. A halfstandard rate turn is 1.5° per second. Two types of

indicators are used to display this information. The

turn-and-slip indicator uses a needle to indicate direction and turn rate. When the needle is aligned with the

white markings, called the turn index, you are in a

standard rate turn. A half-standard rate turn is indicated when the needle is halfway between the indexes.

The turn-and-slip indicator does not indicate roll rate.

The turn coordinator is similar to the turn-and-slip

indicator, but the gyro is canted, which allows it to

sense roll rate in addition to rate of turn. The turn coordinator uses a miniature aircraft to indicate direction,

as well as the turn and roll rate. [Figure 12-7]

Another part of both the turn coordinator and the turnand-slip indicator is the inclinometer. The position of

the ball defines whether the turn is coordinated or not.

The helicopter is either slipping or skidding anytime

the ball is not centered, and usually requires an adjustment of the antitorque pedals or angle of bank to correct it. [Figure 12-8]

INSTRUMENT CHECK—During your preflight, check

to see that the inclinometer is full of fluid and has no

air bubbles. The ball should also be resting at its lowest

point. Since almost all gyroscopic instruments installed

in a helicopter are electrically driven, check to see that

the power indicators are displaying off indications.

Turn the master switch on and listen to the gyros spool

up. There should be no abnormal sounds, such as a

grinding sound, and the power out indicator flags

should not be displayed. After engine start and before

liftoff, set the direction indicator to the magnetic compass. During hover turns, check the heading indicator

for proper operation and ensure that it has not precessed significantly. The turn indicator should also

indicate a turn in the correct direction. During takeoff,

check the attitude indicator for proper indication and

recheck it during the first turn.

MAGNETIC COMPASS

In some helicopters, the magnetic compass is the only

direction seeking instrument. Although the compass

appears to move, it is actually mounted in such a way

that the helicopter turns about the compass card as the

card maintains its alignment with magnetic north.

COMPASS ERRORS

The magnetic compass can only give you reliable

directional information if you understand its limitations

and inherent errors. These include magnetic variation,

compass deviation, and magnetic dip.

MAGNETIC VARIATION

When you fly under visual flight rules, you ordinarily navigate by referring to charts, which are oriented

Figure 12-7. The gyros in both the turn-and-slip indicator and

the turn coordinator are mounted so that they rotate in a vertical plane. The gimbal in the turn coordinator is set at an angle,

or canted, which means precession allows the gyro to sense

both rate of roll and rate of turn. The gimbal in the turn-and-slip

indicator is horizontal. In this case, precession allows the gyro

to sense only rate of turn. When the needle or miniature aircraft

is aligned with the turn index, you are in a standard-rate turn.

Gyro

Rotation

Gimbal

Rotation

TURN-AND-SLIP

INDICATOR

Gimbal

Gimbal

Rotation

Gyro

Rotation

Canted Gyro

TURN

COORDINATOR

Horizontal

Gyro

Inclinometer

Figure 12-8. In a coordinated turn (instrument 1), the ball is

centered. In a skid (instrument 2), the rate of turn is too great

for the angle of bank, and the ball moves to the outside of the

turn. Conversely, in a slip (instrument 3), the rate of turn is

too small for the angle of bank, and the ball moves to the

inside of the turn.

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to true north. Because the aircraft compass is oriented

to magnetic north, you must make allowances for the

difference between these poles in order to navigate

properly. You do this by applying a correction called

variation to convert a true direction to a magnet direction. Variation at a given point is the angular difference between the true and magnetic poles. The amount

of variation depends on where you are located on the

earth’s surface. Isogonic lines connect points where

the variation is equal, while the agonic line defines the

points where the variation is zero. [Figure 12-9]

COMPASS DEVIATION

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Setting Window

Altitude

Indication

Scale

10,000 ft

Pointer

1,000 ft

Pointer

100 ft Pointer

Altimeter Setting

Adjustment Knob

Crosshatch

Flag

A crosshatched

area appears

on some altimeters

when displaying

an altitude below

10,000 feet MSL.

Static Port

Figure 12-3. The main component of the altimeter is a stack of

sealed aneroid wafers. They expand and contract as atmospheric pressure from the static source changes. The mechanical linkage translates these changes into pointer movements on

the indicator.

Diaphragm

Direct Static

Pressure

Calibrated

Leak

Figure 12-4. Although the sealed case and diaphragm are

both connected to the static port, the air inside the case is

restricted through a calibrated leak. When the pressures are

equal, the needle reads zero. As you climb or descend, the

pressure inside the diaphragm instantly changes, and the

needle registers a change in vertical direction. When the

pressure differential stabilizes at a definite ratio, the needle

registers the rate of altitude change.

12-3

ways. If the ram air inlet is clogged, but the drain hole

remains open, the airspeed indicator registers zero, regardless of airspeed. If both the ram air inlet and the drain hole

become blocked, pressure in the line is trapped, and the

airspeed indicator reacts like an altimeter, showing an

increase in airspeed with an increase in altitude, and a

decrease in speed as altitude decreases. This occurs as

long as the static port remains unobstructed.

If the static port alone becomes blocked, the airspeed

indicator continues to function, but with incorrect readings. When you are operating above the altitude where

the static port became clogged, the airspeed indicator

reads lower than it should. Conversely, when operating

below that altitude, the indicator reads higher than the

correct value. The amount of error is proportional to

the distance from the altitude where the static system

became blocked. The greater the difference, the greater

the error. With a blocked static system, the altimeter

freezes at the last altitude and the VSI freezes at zero.

Both instruments are then unusable.

Some helicopters are equipped with an alternate static

source, which may be selected in the event that the main

static system becomes blocked. The alternate source generally vents into the cabin, where air pressures are slightly

different than outside pressures, so the airspeed and

altimeter usually read higher than normal. Correction

charts may be supplied in the flight manual.

GYROSCOPIC INSTRUMENTS

The three gyroscopic instruments that are required for

instrument flight are the attitude indicator, heading

indicator, and turn indicator. When installed in helicopters, these instruments are usually electrically powered.

Gyros are affected by two principles—rigidity in space and

precession. Rigidity in space means that once a gyro is

spinning, it tends to remain in a fixed position and resists

external forces applied to it. This principle allows a gyro to

be used to measure changes in attitude or direction.

Precession is the tilting or turning of a gyro in response to

pressure. The reaction to this pressure does not occur at

the point where it was applied; rather, it occurs at a point

that is 90° later in the direction of rotation from where the

pressure was applied. This principle allows the gyro to

determine a rate of turn by sensing the amount of pressure created by a change in direction. Precession can also

create some minor errors in some instruments.

ATTITUDE INDICATOR

The attitude indicator provides a substitute for the natural horizon. It is the only instrument that provides an

immediate and direct indication of the helicopter’s

pitch and bank attitude. Since most attitude indicators

installed in helicopters are electrically powered, there

may be a separate power switch, as well as a warning

flag within the instrument, that indicates a loss of

power. A caging or “quick erect” knob may be

included, so you can stabilize the spin axis if the gyro

has tumbled. [Figure 12-5]

HEADING INDICATOR

The heading indicator, which is sometimes referred to

as a directional gyro (DG), senses movement around

the vertical axis and provides a more accurate heading

reference compared to a magnetic compass, which has

a number of turning errors. [Figure 12-6].

Bank Index

Gyro

Gimbal

Rotation

Roll

Gimbal

Pitch

Gimbal

Horizon

Reference

Arm

Figure 12-5. The gyro in the attitude indicator spins in the

horizontal plane. Two mountings, or gimbals, are used so

that both pitch and roll can be sensed simultaneously. Due to

rigidity in space, the gyro remains in a fixed position relative

to the horizon as the case and helicopter rotate around it.

Adjustment Gears

Adjustment

Knob

Gimbal

Rotation

Gimbal Gyro

Main

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pressure in the event the main port becomes blocked.

[Figure 12-1]

AIRSPEED INDICATOR

The airspeed indicator displays the speed of the helicopter through the air by comparing ram air pressure

from the pitot tube with static air pressure from the

static port—the greater the differential, the greater the

speed. The instrument displays the result of this pressure differential as indicated airspeed (IAS).

Manufacturers use this speed as the basis for determining helicopter performance, and it may be displayed in

knots, miles per hour, or both. [Figure 12-2] When an

indicated airspeed is given for a particular situation,

you normally use that speed without making a correction for altitude or temperature. The reason no correc-

tion is needed is that an airspeed indicator and aircraft

performance are affected equally by changes in air density. An indicated airspeed always yields the same

performance because the indicator has, in fact, compensated for the change in the environment.

INSTRUMENT CHECK—During the preflight, ensure

that the pitot tube, drain hole, and static ports are unobstructed. Before liftoff, make sure the airspeed indicator

is reading zero. If there is a strong wind blowing directly

at the helicopter, the airspeed indicator may read higher

Pitot

Heater Switch

Pitot

Tube

Airspeed

Indicator

Vertical

Speed

Indicator

(VSI) Altimeter

Drain

Opening

Static Port

ON

OFF

Alternate Static Source

ALT

STATIC AIR

PULL ON

Figure 12-1. Ram air pressure is supplied only to the airspeed

indicator, while static pressure is used by all three instruments. Electrical heating elements may be installed to prevent ice from forming on the pitot tube. A drain opening to

remove moisture is normally included.

Diaphragm

Static Air Line

Ram Air

Pitot Tube

Figure 12-2. Ram air pressure from the pitot tube is directed

to a diaphragm inside the airspeed indicator. The airtight

case is vented to the static port. As the diaphragm expands

or contracts, a mechanical linkage moves the needle on the

face of the indicator.

12-2

than zero, depending on the wind speed and direction.

As you begin your takeoff, make sure the airspeed indicator is increasing at an appropriate rate. Keep in mind,

however, that the airspeed indication might be unreliable below a certain airspeed due to rotor downwash.

ALTIMETER

The altimeter displays altitude in feet by sensing pressure changes in the atmosphere. There is an adjustable

barometric scale to compensate for changes in atmospheric pressure. [Figure 12-3]

The basis for altimeter calibration is the International

Standard Atmosphere (ISA), where pressure, temperature, and lapse rates have standard values. However,

actual atmospheric conditions seldom match the standard values. In addition, local pressure readings within

a given area normally change over a period of time, and

pressure frequently changes as you fly from one area to

another. As a result, altimeter indications are subject to

errors, the extent of which depends on how much the

pressure, temperature, and lapse rates deviate from standard, as well as how recently you have set the altimeter.

The best way to minimize altimeter errors is to update

the altimeter setting frequently. In most cases, use the

current altimeter setting of the nearest reporting station

along your route of flight per regulatory requirements.

INSTRUMENT CHECK—During the preflight, ensure

that the static ports are unobstructed. Before lift-off, set

the altimeter to the current setting. If the altimeter indicates within 75 feet of the actual elevation, the altimeter

is generally considered acceptable for use.

VERTICAL SPEED INDICATOR

The vertical speed indicator (VSI) displays the rate of

climb or descent in feet per minute (f.p.m.) by measuring how fast the ambient air pressure increases or

decreases as the helicopter changes altitude. Since the

VSI measures only the rate at which air pressure

changes, air temperature has no effect on this instrument. [Figure 12-4]

There is a lag associated with the reading on the VSI,

and it may take a few seconds to stabilize when showing rate of climb or descent. Rough control technique

and turbulence can further extend the lag period and

cause erratic and unstable rate indications. Some aircraft are equipped with an instantaneous vertical speed

indicator (IVSI), which incorporates accelerometers to

compensate for the lag found in the typical VSI.

INSTRUMENT CHECK—During the preflight, ensure

that the static ports are unobstructed. Check to see that

the VSI is indicating zero before lift-off. During takeoff,

check for a positive rate of climb indication.

SYSTEM ERRORS

The pitot-static system and associated instruments are

usually very reliable. Errors are generally caused when

the pitot or static openings are blocked. This may be

caused by dirt, ice formation, or insects. Check the pitot

and static openings for obstructions during the preflight.

It is also advisable to place covers on the pitot and static

ports when the helicopter is parked on the ground.

The airspeed indicator is the only instrument affected by a

blocked pitot tube. The system can become clogged in two

Aneroid

Wafers

Altimeter

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an advantage over airplanes, as they can land almost

anywhere before they run out of fuel.

If you are lost, there are some good common sense

procedures to follow. If you are nowhere near or cannot

see a town or city, the first thing you should do is climb.

An increase in altitude increases radio and navigation

reception range, and also increases radar coverage. If

you are flying near a town or city, you may be able to

read the name of the town on a water tower or even land

to ask directions.

If your helicopter has a navigational radio, such as a

VOR or ADF receiver, you can possibly determine

your position by plotting your azimuth from two or

more navigational facilities. If GPS is installed, or you

have a portable aviation GPS on board, you can use it

to determine your position and the location of the

nearest airport.

Communicate with any available facility using

frequencies shown on the sectional chart. If you are

able to communicate with a controller, you may be

offered radar vectors. Other facilities may offer

direction finding (DF) assistance. To use this

procedure, the controller will request you to hold

down your transmit button for a few seconds and

then release it. The controller may ask you to change

directions a few times and repeat the transmit

procedure. This gives the controller enough information to plot your position and then give you vectors to a suitable landing sight. If your situation

becomes threatening, you can transmit your problems on the emergency frequency 121.5 MHZ and

set your transponder to 7700. Most facilities, and

even airliners, monitor the emergency frequency.

EMERGENCY EQUIPMENT AND

SURVIVAL GEAR

Both Canada and Alaska require pilots to carry survival

gear. However, it is good common sense that any time

you are flying over rugged and desolated terrain, consider carrying survival gear. Depending on the size and

storage capacity of your helicopter, the following are

some suggested items:

• Food that is not subject to deterioration due to

heat or cold. There should be at least 10,000 calo-

ries for each person on board, and it should be

stored in a sealed waterproof container. It should

have been inspected by the pilot or his representative within the previous six months, and bear a

label 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 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 ELT with spare batteries.

Additional items when there are no trees:

• 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.

• Honing stone or file.

• Ice chisel.

• Snow knife or saw knife.

12-1

Attitude instrument flying in helicopters is essentially

visual flying with the flight instruments substituted for

the various reference points on the helicopter and the

natural horizon. Control changes, required to produce a

given attitude by reference to instruments, are identical

to those used in helicopter VFR flight, and your

thought processes are the same. Basic instrument training is intended as a building block towards attaining an

instrument rating. It will also enable you to do a 180°

turn in case of inadvertent incursion into instrument

meteorological conditions (IMC).

FLIGHT INSTRUMENTS

When flying a helicopter with reference to the flight

instruments, proper instrument interpretation is the

basis for aircraft control. Your skill, in part, depends on

your understanding of how a particular instrument or

system functions, including its indications and limitations. With this knowledge, you can quickly determine

what an instrument is telling you and translate that

information into a control response.

PITOT-STATIC INSTRUMENTS

The pitot-static instruments, which include the airspeed

indicator, altimeter, and vertical speed indicator, operate on the principle of differential air pressure. Pitot

pressure, also called impact, ram, or dynamic pressure,

is directed only to the airspeed indicator, while static

pressure, or ambient pressure, is directed to all three

instruments. An alternate static source may be included

allowing you to select an alternate source of ambient

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be vertical, lateral, horizontal, or even a combination.

Normally, the direction of the vibration can be determined by concentrating on the feel of the vibration,

which may push you up and down, backwards and

forwards, or from side to side. The direction of the

vibration and whether it is felt in the controls or the

airframe is an important means for the mechanic

to troubleshoot the source. Some possible causes

could be that the main rotor blades are out of track or

balance, damaged blades, worn bearings, dampers out

of adjustment, or worn parts.

MEDIUM AND HIGH FREQUENCY VIBRATIONS

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

minute) and high frequency vibrations (2,000 cycles

per minute or higher) are normally associated with outof-balance components that rotate at a high r.p.m., such

as the tail rotor, engine, cooling fans, and components

of the drive train, including transmissions, drive shafts,

bearings, pulleys, and belts. Most tail rotor vibrations

can be felt through the tail rotor pedals as long as there

are no hydraulic actuators, which usually dampen out

the vibration. Any imbalance in the tail rotor system 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 r.p.m.

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.

FLIGHT DIVERSION

There will probably come a time in your flight career

when you will not be able to make it to your destination.

This can be the result of unpredictable weather conditions,

a system malfunction, or poor preflight planning. In any

case, you will need to be able to safely and efficiently

divert to an alternate destination. Before any crosscountry flight, check the charts for airports or suitable

landing areas along or near your route of flight. Also,

check for navaids that can be used during a diversion.

Computing course, time, speed, and distance information in flight requires the same computations used

during preflight planning. However, because of the

limited cockpit space, and because you must divide

your attention between flying the helicopter, making

calculations, and scanning for other aircraft, you should

take advantage of all possible shortcuts and rule-ofthumb computations.

When in flight, it is rarely practical to actually plot a

course on a sectional chart and mark checkpoints and

distances. Furthermore, because an alternate airport is

usually not very far from your original course, actual

plotting is seldom necessary.

A course to an alternate can be measured accurately

with a protractor or plotter, but can also be measured

with reasonable accuracy using a straightedge and the

compass rose depicted around VOR stations. This

approximation can be made on the basis of a radial

from a nearby VOR or an airway that closely parallels

the course to your alternate. However, you must

remember that the magnetic heading associated with

a VOR radial or printed airway is outbound from

the station. To find the course TO the station, it may

be necessary to determine the reciprocal of the

indicated heading.

Distances can be determined by using a plotter, or by

placing a finger or piece of paper between the two and

then measuring the approximate distance on the

mileage scale at the bottom of the chart.

Before changing course to proceed to an alternate, you

should first consider the relative distance and route of

flight to all suitable alternates. In addition, you should

consider the type of terrain along the route. If circumstances warrant, and your helicopter is equipped with

navigational equipment, it is typically easier to navigate to an alternate airport that has a VOR or NDB

facility on the field.

After you select the most appropriate alternate, approximate the magnetic course to the alternate using

a compass rose or airway on the sectional chart. If time

permits, try to start the diversion over a prominent

ground feature. However, in an emergency, divert

promptly toward your alternate. To complete all

plotting, measuring, and computations involved before

diverting to the alternate may only aggravate an

actual emergency.

Once established on course, note the time, and then

use the winds aloft nearest to your diversion point to

calculate a heading and groundspeed. Once you have

calculated your groundspeed, determine a new arrival

time and fuel consumption.

11-16

You must give priority to flying the helicopter while

dividing your attention between navigation and

planning. When determining an altitude to use while

diverting, you should consider cloud heights, winds,

terrain, and radio reception.

LOST PROCEDURES

Getting lost in an aircraft is a potentially dangerous

situation especially when low on fuel. Helicopters have