PilotHandbook

1 Airspeed trend vector There are two fundamental properties of gyroscopic action:
150 rigidity in space and precession.

0 140 Rigidity in Space
1310 Rigidity in space refers to the principle that a gyroscope
120 remains in a fixed position in the plane in which it is spinning.
9 An example of rigidity in space is that of a bicycle wheel.
110 As the bicycle wheels increase speed, they become more and
more stable in their plane of rotation. This is why a bicycle is
very unstable and very maneuverable at low speeds and very
stable and less maneuverable at higher speeds.

100 By mounting this wheel, or gyroscope, on a set of gimbal
90 rings, the gyro is able to rotate freely in any direction. Thus,
if the gimbal rings are tilted, twisted, or otherwise moved,
TAS 120KT the gyro remains in the plane in which it was originally
spinning. [Figure 7-18]
Figure 7-17. Altimeter trend vector.

ADC computes the rate of change and displays the 6-second
projection of where the aircraft will be. Pilots can utilize
the trend vectors to better control the aircraft’s attitude. By
including the trend vectors in the instrument scan, pilots are
able to precisely control airspeed and altitude. Additional
information can be obtained by referencing the Instrument
Flying Handbook or specific avionics manufacturer’s training
material.

Gyroscopic Flight Instruments

Several flight instruments utilize the properties of a gyroscope
for their operation. The most common instruments containing
gyroscopes are the turn coordinator, heading indicator, and
the attitude indicator. To understand how these instruments
operate requires knowledge of the instrument power systems,
gyroscopic principles, and the operating principles of each
instrument.

Gyroscopic Principles Figure 7-18. Regardless of the position of its base, a gyro tends to
Any spinning object exhibits gyroscopic properties. A wheel remain rigid in space, with its axis of rotation pointed in a constant
or rotor designed and mounted to utilize these properties is direction.
called a gyroscope. Two important design characteristics of an
instrument gyro are great weight for its size, or high density, Precession
and rotation at high speed with low friction bearings. Precession is the tilting or turning of a gyro in response to a
deflective force. The reaction to this force does not occur at
There are two general types of mountings; the type used the point at which it was applied; rather, it occurs at a point
depends upon which property of the gyro is utilized. A freely that is 90° later in the direction of rotation. This principle
or universally mounted gyroscope is free to rotate in any allows the gyro to determine a rate of turn by sensing the
direction about its center of gravity. Such a wheel is said to amount of pressure created by a change in direction. The rate
have three planes of freedom. The wheel or rotor is free to at which the gyro precesses is inversely proportional to the
rotate in any plane in relation to the base and is balanced so speed of the rotor and proportional to the deflective force.
that, with the gyro wheel at rest, it remains in the position
in which it is placed. Restricted or semi-rigidly mounted
gyroscopes are those mounted so that one of the planes of
freedom is held fixed in relation to the base.

7-15

Using the example of the bicycle, precession acts on the or pressure required for instrument operation varies, but is
wheels in order to allow the bicycle to turn. While riding usually between 4.5 "Hg and 5.5 "Hg.
at normal speed, it is not necessary to turn the handle bars
in the direction of the desired turn. A rider simply leans in One source of vacuum for the gyros is a vane-type engine-
the direction that he or she wishes to go. Since the wheels driven pump that is mounted on the accessory case of
are rotating in a clockwise direction when viewed from the the engine. Pump capacity varies in different airplanes,
right side of the bicycle, if a rider leans to the left, a force is depending on the number of gyros.
applied to the top of the wheel to the left. The force actually
acts 90° in the direction of rotation, which has the effect of A typical vacuum system consists of an engine-driven
applying a force to the front of the tire, causing the bicycle vacuum pump, relief valve, air filter, gauge, and tubing
to move to the left. There is a need to turn the handlebars at necessary to complete the connections. The gauge is mounted
low speeds because of the instability of the slowly turning in the aircraft’s instrument panel and indicates the amount
gyros, and also to increase the rate of turn. of pressure in the system (vacuum is measured in inches of
mercury less than ambient pressure).
Precession can also create some minor errors in some
instruments. [Figure 7-19] Precession can cause a freely As shown in Figure 7-20, air is drawn into the vacuum system
spinning gyro to become displaced from its intended plane by the engine-driven vacuum pump. It first goes through
of rotation through bearing friction, etc. Certain instruments a filter, which prevents foreign matter from entering the
may require corrective realignment during flight, such as the vacuum or pressure system. The air then moves through the
heading indicator. attitude and heading indicators, where it causes the gyros
to spin. A relief valve prevents the vacuum pressure, or
Plane of Rotation Plane of Force suction, from exceeding prescribed limits. After that, the air
is expelled overboard or used in other systems, such as for
FORCE inflating pneumatic deicing boots.

Plane of Precession It is important to monitor vacuum pressure during flight,
because the attitude and heading indicators may not provide
reliable information when suction pressure is low. The
vacuum, or suction, gauge is generally marked to indicate
the normal range. Some aircraft are equipped with a warning
light that illuminates when the vacuum pressure drops below
the acceptable level.

When the vacuum pressure drops below the normal operating
range, the gyroscopic instruments may become unstable and
inaccurate. Cross checking the instruments routinely is a
good habit to develop.

Figure 7-19. Precession of a gyroscope resulting from an applied Turn Indicators
deflective force. Aircraft use two types of turn indicators: turn-and-slip
indicator and turn coordinator. Because of the way the gyro
Sources of Power is mounted, the turn-and-slip indicator shows only the rate of
In some aircraft, all the gyros are vacuum, pressure, or turn in degrees per second. The turn coordinator is mounted
electrically operated. In other aircraft, vacuum or pressure at an angle, or canted, so it can initially show roll rate. When
systems provide the power for the heading and attitude the roll stabilizes, it indicates rate of turn. Both instruments
indicators, while the electrical system provides the power for indicate turn direction and quality (coordination), and also
the turn coordinator. Most aircraft have at least two sources serve as a backup source of bank information in the event an
of power to ensure at least one source of bank information is attitude indicator fails. Coordination is achieved by referring
available if one power source fails. The vacuum or pressure to the inclinometer, which consists of a liquid-filled curved
system spins the gyro by drawing a stream of air against the tube with a ball inside. [Figure 7-21]
rotor vanes to spin the rotor at high speed, much like the
operation of a waterwheel or turbine. The amount of vacuum

7-16

Typical vacuum system

33 3 Heading Indicator Vacuum relief valve

24 30 6 I2 Overboard vent line
Vacuum pump
I5 2I
Vacuum air filter
20 20
I0 I0

I0 I0
20 20

STBY PWR TEST

46

2 SUCTION 8

INCHES MERCURT Suction Attitude Indicator
Gauge
0 I0

Figure 7-20. Typical vacuum system.

Turn-and-Slip Indicator invalid. Certain instruments have specific pitch and bank
limits that induce a tumble of the gyro.
The gyro in the turn-and-slip indicator rotates in the vertical
plane, corresponding to the aircraft’s longitudinal axis. A Turn Coordinator
single gimbal limits the planes in which the gyro can tilt, and The gimbal in the turn coordinator is canted; therefore, its
a spring tries to return it to center. Because of precession, a gyro can sense both rate of roll and rate of turn. Since turn
yawing force causes the gyro to tilt left or right, as viewed coordinators are more prevalent in training aircraft, this
from the pilot seat. The turn-and-slip indicator uses a pointer, discussion concentrates on that instrument. When rolling into
called the turn needle, to show the direction and rate of turn. or out of a turn, the miniature aircraft banks in the direction
The turn-and-slip indicator is incapable of “tumbling” off the aircraft is rolled. A rapid roll rate causes the miniature
its rotational axis because of the restraining springs. When aircraft to bank more steeply than a slow roll rate.
extreme forces are applied to a gyro, the gyro is displaced
from its normal plane of rotation, rendering its indications

Gimbal Gimbal rotation Horizontal gyro
Gyro rotation

Gimbal rotation

Gyro rotation

Canted gyro Standard rate turn index
Standard rate turn index
Inclinometer Inclinometer

Turn coordinator Turn-and-slip indicator

Figure 7-21. Turn indicators rely on controlled precession for their operation.

7-17

The turn coordinator can be used to establish and maintain turn is too great for the angle of bank, and the ball moves
a standard-rate turn by aligning the wing of the miniature to the outside of the turn. To correct for these conditions,
aircraft with the turn index. Figure 7-22 shows a picture of a and improve the quality of the turn, remember to “step on
turn coordinator. There are two marks on each side (left and the ball.” Varying the angle of bank can also help restore
right) of the face of the instrument. The first mark is used to coordinated flight from a slip or skid. To correct for a slip,
reference a wings level zero rate of turn. The second mark decrease bank and/or increase the rate of turn. To correct for
on the left and right side of the instrument serve to indicate a skid, increase the bank and/or decrease the rate of turn.
a standard rate of turn. A standard-rate turn is defined as a
turn rate of 3° per second. The turn coordinator indicates only Yaw String
the rate and direction of turn; it does not display a specific One additional tool which can be added to the aircraft is a
angle of bank. yaw string. A yaw string is simply a string or piece of yarn
attached to the center of the wind screen. When in coordinated
D.C. D.C. flight, the string trails straight back over the top of the wind
ELEC. ELEC. screen. When the aircraft is either slipping or skidding,
the yaw string moves to the right or left depending on the
TURN COORDINATOR TURN COORDINATOR direction of slip or skid.

L 2 MIN. R L 2 MIN. R Instrument Check
During the preflight, check to see that the inclinometer is
NO PITCH NO PITCH full of fluid and has no air bubbles. The ball should also be
INFORMATION INFORMATION resting at its lowest point. When taxiing, the turn coordinator
should indicate a turn in the correct direction while the ball
Slipping turn Skidding turn moves opposite the direction of the turn.

D.C.
ELEC.

TURN COORDINATOR Attitude Indicator
The attitude indicator, with its miniature aircraft and horizon
L 2 MIN. R bar, displays a picture of the attitude of the aircraft. The
relationship of the miniature aircraft to the horizon bar is
NO PITCH the same as the relationship of the real aircraft to the actual
INFORMATION horizon. The instrument gives an instantaneous indication of
even the smallest changes in attitude.
Coordinated turn
The gyro in the attitude indicator is mounted in a horizontal
Figure 7-22. If inadequate right rudder is applied in a right turn, a plane and depends upon rigidity in space for its operation.
slip results. Too much right rudder causes the aircraft to skid through The horizon bar represents the true horizon. This bar is
the turn. Centering the ball results in a coordinated turn. fixed to the gyro and remains in a horizontal plane as the
aircraft is pitched or banked about its lateral or longitudinal
Inclinometer axis, indicating the attitude of the aircraft relative to the true
The inclinometer is used to depict aircraft yaw, which is horizon. [Figure 7-23]
the side-to-side movement of the aircraft’s nose. During
coordinated, straight-and-level flight, the force of gravity The gyro spins in the horizontal plane and resists deflection of
causes the ball to rest in the lowest part of the tube, centered the rotational path. Since the gyro relies on rigidity in space,
between the reference lines. Coordinated flight is maintained the aircraft actually rotates around the spinning gyro.
by keeping the ball centered. If the ball is not centered, it can
be centered by using the rudder. An adjustment knob is provided with which the pilot may
move the miniature aircraft up or down to align the miniature
To center the ball, apply rudder pressure on the side to which aircraft with the horizon bar to suit the pilot’s line of vision.
the ball is deflected. Use the simple rule, “step on the ball,” to Normally, the miniature aircraft is adjusted so that the wings
remember which rudder pedal to press. If aileron and rudder overlap the horizon bar when the aircraft is in straight-and-
are coordinated during a turn, the ball remains centered in the level cruising flight.
tube. If aerodynamic forces are unbalanced, the ball moves
away from the center of the tube. As shown in Figure 7-22, in
a slip, the rate of turn is too slow for the angle of bank, and
the ball moves to the inside of the turn. In a skid, the rate of

7-18

Attitude indicator Bank index The pitch and bank limits depend upon the make and model
Gimbal rotation of the instrument. Limits in the banking plane are usually
from 100° to 110°, and the pitch limits are usually from 60°
20 2 20 to 70°. If either limit is exceeded, the instrument will tumble
I0 or spill and will give incorrect indications until realigned. A
I0 I0 number of modern attitude indicators do not tumble.
0
Every pilot should be able to interpret the banking scale
I0 I0 I0 illustrated in Figure 7-24. Most banking scale indicators on
20 the top of the instrument move in the same direction from
20 that in which the aircraft is actually banked. Some other
models move in the opposite direction from that in which the
BY PWR TEST aircraft is actually banked. This may confuse the pilot if the
indicator is used to determine the direction of bank. This scale
Roll gimbal Horizon reference arm should be used only to control the degree of desired bank.
Gyro Pitch gimbal The relationship of the miniature aircraft to the horizon bar
should be used for an indication of the direction of bank.
Figure 7-23. Attitude indicator.

20 20 20 20
I0 I0 I0
I0 20 20 I0 I0
I0
20 I0 20 I0 I0 I0 I0 20
20 20
20

STBY PWR TEST STBY PWR TEST STBY PWR TEST

Climbing left bank Straight climb Climbing right bank

Pointer

20 10° 20° Ban k scale 20
I0 30°
I0 20 45° 20 I0 I0
I0
20 I0 20 20 20 60° I0 I0 20
I0 I0 90°
20
I0 I0
STBY PWR TEST 20 20 STBY PWR TEST

STBY PWR TEST

Level left bank Artificial horizon Adjustment knob Level right bank

20 20 20 20
I0 I0 I0
I0 20 20 I0 I0
I0 I0 I0
20 I0 20 20 20 I0 I0 20

20

STBY PWR TEST STBY PWR TEST STBY PWR TEST

Descending left bank Straight descent Descending right bank

Figure 7-24. Attitude representation by the attitude indicator corresponds to the relation of the aircraft to the real horizon.

7-19

The attitude indicator is reliable and the most realistic flight caused by friction, the heading indicator may indicate as
instrument on the instrument panel. Its indications are very much as 15° error per every hour of operation.
close approximations of the actual attitude of the aircraft.
Some heading indicators referred to as horizontal situation
Heading Indicator indicators (HSI) receive a magnetic north reference from
The heading indicator is fundamentally a mechanical a magnetic slaving transmitter, and generally need no
instrument designed to facilitate the use of the magnetic adjustment. The magnetic slaving transmitter is called a
compass. Errors in the magnetic compass are numerous, magnetometer.
making straight flight and precision turns to headings difficult
to accomplish, particularly in turbulent air. A heading Attitude and Heading Reference System (AHRS)
indicator, however, is not affected by the forces that make Electronic flight displays have replaced free-spinning gyros
the magnetic compass difficult to interpret. [Figure 7-25] with solid-state laser systems that are capable of flight at
any attitude without tumbling. This capability is the result
Heading indicator of the development of the Attitude and Heading Reference
System (AHRS).
Main drive gear Compass card gear

Gimbal rotation The AHRS sends attitude information to the PFD in order
to generate the pitch and bank information of the attitude
33 3 indicator. The heading information is derived from a
magnetometer which senses the earth’s lines of magnetic
6 I2 flux. This information is then processed and sent out to the
PFD to generate the heading display. [Figure 7-26]

I5 2I

Gimbal Adjustment gears

Gyro Adjustment knob

Figure 7-25. A heading indicator displays headings based on a 360°
azimuth, with the final zero omitted. For example, “6” represents
060°, while “21” indicates 210°. The adjustment knob is used to
align the heading indicator with the magnetic compass.

The operation of the heading indicator depends upon the Figure 7-26. Attitude and heading reference system (AHRS).
principle of rigidity in space. The rotor turns in a vertical
plane and fixed to the rotor is a compass card. Since the rotor The Flux Gate Compass System
remains rigid in space, the points on the card hold the same As mentioned earlier, the lines of flux in the Earth’s magnetic
position in space relative to the vertical plane of the gyro. The field have two basic characteristics: a magnet aligns with
aircraft actually rotates around the rotating gyro, not the other them, and an electrical current is induced, or generated, in
way around. As the instrument case and the aircraft revolve any wire crossed by them.
around the vertical axis of the gyro, the card provides clear
and accurate heading information. The flux gate compass that drives slaved gyros uses the
characteristic of current induction. The flux valve is a small,
Because of precession caused by friction, the heading segmented ring, like the one in Figure 7-27, made of soft iron
indicator creeps or drifts from a heading to which it is set. that readily accepts lines of magnetic flux. An electrical coil
Among other factors, the amount of drift depends largely is wound around each of the three legs to accept the current
upon the condition of the instrument. If the bearings are worn,
dirty, or improperly lubricated, the drift may be excessive.
Another error in the heading indicator is caused by the fact
that the gyro is oriented in space, and the Earth rotates in
space at a rate of 15° in 1 hour. Thus, discounting precession

7-20

Figure 7-28. The current in each of the three pickup coils changes
with the heading of the aircraft..

Figure 7-27. The soft iron frame of the flux valve accepts the flux The slaving control and compensator unit has a push button
from the Earth’s magnetic field each time the current in the center that provides a means of selecting either the “slaved gyro”
coil reverses. This flux causes current to flow in the three pickup or “free gyro” mode. This unit also has a slaving meter
coils. and two manual heading-drive buttons. The slaving meter
indicates the difference between the displayed heading and
induced in this ring by the Earth’s magnetic field. A coil the magnetic heading. A right deflection indicates a clockwise
wound around the iron spacer in the center of the frame has error of the compass card; a left deflection indicates a
400 Hz alternating current (AC) flowing through it. During counterclockwise error. Whenever the aircraft is in a turn
the times when this current reaches its peak, twice during and the card rotates, the slaving meter shows a full deflection
each cycle, there is so much magnetism produced by this to one side or the other. When the system is in “free gyro”
coil that the frame cannot accept the lines of flux from the mode, the compass card may be adjusted by depressing the
Earth’s field. appropriate heading-drive button.

A separate unit, the magnetic slaving transmitter is mounted
remotely, usually in a wingtip to eliminate the possibility of

As the current reverses between the peaks, it demagnetizes
the frame so it can accept the flux from the Earth’s field. As
this flux cuts across the windings in the three coils, it causes
current to flow in them. These three coils are connected in
such a way that the current flowing in them changes as the
heading of the aircraft changes. [Figure 7-28]

The three coils are connected to three similar but smaller coils
in a synchro inside the instrument case. The synchro rotates
the dial of a radio magnetic indicator (RMI) or a HSI.

Remote Indicating Compass Figure 7-29. Pictorial navigation indicator (HSI, top), slaving meter
Remote indicating compasses were developed to compensate (lower right), and slaving control compensator unit (lower left).
for the errors and limitations of the older type of heading
indicators. The two panel-mounted components of a typical
system are the pictorial navigation indicator and the slaving
control and compensator unit. [Figure 7-29] The pictorial
navigation indicator is commonly referred to as an HSI.

7-21

magnetic interference. It contains the flux valve, which is The bank and pitch limits of the heading indicator vary
the direction-sensing device of the system. A concentration with the particular design and make of instrument. On some
of lines of magnetic force, after being amplified, becomes heading indicators found in light aircraft, the limits are
a signal relayed to the heading indicator unit, which is also approximately 55° of pitch and 55° of bank. When either of
remotely mounted. This signal operates a torque motor in these attitude limits is exceeded, the instrument “tumbles”
the heading indicator unit that processes the gyro unit until or “spills” and no longer gives the correct indication until
it is aligned with the transmitter signal. The magnetic slaving reset. After spilling, it may be reset with the caging knob.
transmitter is connected electrically to the HSI. Many of the modern instruments used are designed in such
a manner that they do not tumble.
There are a number of designs of the remote indicating
compass; therefore, only the basic features of the system are An additional precession error may occur due to a gyro not
covered here. Instrument pilots must become familiar with spinning fast enough to maintain its alignment. When the
the characteristics of the equipment in their aircraft. vacuum system stops producing adequate suction to maintain
the gyro speed, the heading indicator and the attitude indicator
As instrument panels become more crowded and the pilot’s gyros begin to slow down. As they slow, they become more
available scan time is reduced by a heavier flight deck susceptible to deflection from the plane of rotation. Some
workload, instrument manufacturers have worked toward aircraft have warning lights to indicate that a low vacuum
combining instruments. One good example of this is the situation has occurred. Other aircraft may have only a vacuum
RMI in Figure 7-30. The compass card is driven by signals gauge that indicates the suction.
from the flux valve, and the two pointers are driven by an
automatic direction finder (ADF) and a very high frequency Instrument Check
(VHF) omni-directional radio range (VOR). As the gyro spools up, make sure there are no abnormal
sounds. While taxiing, the instrument should indicate turns in
the correct direction, and precession should not be abnormal.
At idle power settings, the gyroscopic instruments using the
vacuum system might not be up to operating speeds and
precession might occur more rapidly than during flight.

Compass Systems

The Earth is a huge magnet, spinning in space, surrounded
by a magnetic field made up of invisible lines of flux. These
lines leave the surface at the magnetic north pole and reenter
at the magnetic South Pole.

Figure 7-30. Driven by signals from a flux valve, the compass card Lines of magnetic flux have two important characteristics:
in this RMI indicates the heading of the aircraft opposite the upper any magnet that is free to rotate will align with them, and
center index mark. The green pointer is driven by the ADF. an electrical current is induced into any conductor that cuts
across them. Most direction indicators installed in aircraft
Heading indicators that do not have this automatic make use of one of these two characteristics.
northseeking capability are called “free” gyros, and require
periodic adjustment. It is important to check the indications Magnetic Compass
frequently (approximately every 15 minutes) and reset the One of the oldest and simplest instruments for indicating
heading indicator to align it with the magnetic compass direction is the magnetic compass. It is also one of the basic
when required. Adjust the heading indicator to the magnetic instruments required by Title 14 of the Code of Federal
compass heading when the aircraft is straight and level at a Regulations (14 CFR) part 91 for both VFR and IFR flight.
constant speed to avoid compass errors.
A magnet is a piece of material, usually a metal containing
iron, which attracts and holds lines of magnetic flux.
Regardless of size, every magnet has two poles: north and
south. When one magnet is placed in the field of another, the
unlike poles attract each other, and like poles repel.

7-22

An aircraft magnetic compass, such as the one in Figure 7-30, A compensator assembly mounted on the top or bottom
has two small magnets attached to a metal float sealed inside a of the compass allows an aviation maintenance technician
bowl of clear compass fluid similar to kerosene. A graduated (AMT) to create a magnetic field inside the compass housing
scale, called a card, is wrapped around the float and viewed that cancels the influence of local outside magnetic fields.
through a glass window with a lubber line across it. The card This is done to correct for deviation error. The compensator
is marked with letters representing the cardinal directions, assembly has two shafts whose ends have screwdriver slots
north, east, south, and west, and a number for each 30° accessible from the front of the compass. Each shaft rotates
between these letters. The final “0” is omitted from these one or two small compensating magnets. The end of one shaft
directions. For example, 3 = 30°, 6 = 60°, and 33 = 330°. is marked E-W, and its magnets affect the compass when the
There are long and short graduation marks between the letters aircraft is pointed east or west. The other shaft is marked
and numbers, each long mark representing 10° and each short N-S and its magnets affect the compass when the aircraft is
mark representing 5°. pointed north or south.

Magnetic Compass Induced Errors

The magnetic compass is the simplest instrument in the
panel, but it is subject to a number of errors that must be
considered.

Figure 7-31. A magnetic compass. The vertical line is called the Variation
lubber line.
The Earth rotates about its geographic axis; maps and charts
The float and card assembly has a hardened steel pivot in its are drawn using meridians of longitude that pass through the
center that rides inside a special, spring-loaded, hard glass geographic poles. Directions measured from the geographic
jewel cup. The buoyancy of the float takes most of the weight poles are called true directions. The magnetic North Pole to
off the pivot, and the fluid damps the oscillation of the float which the magnetic compass points is not collocated with
and card. This jewel-and-pivot type mounting allows the float the geographic North Pole, but is some 1,300 miles away;
freedom to rotate and tilt up to approximately 18° angle of directions measured from the magnetic poles are called
bank. At steeper bank angles, the compass indications are magnetic directions. In aerial navigation, the difference
erratic and unpredictable. between true and magnetic directions is called variation. This
same angular difference in surveying and land navigation is
The compass housing is entirely full of compass fluid. To called declination.
prevent damage or leakage when the fluid expands and
contracts with temperature changes, the rear of the compass Figure 7-32 shows the isogonic lines that identify the number
case is sealed with a flexible diaphragm, or with a metal of degrees of variation in their area. The line that passes near
bellows in some compasses. Chicago is called the agonic line. Anywhere along this line
the two poles are aligned, and there is no variation. East
of this line, the magnetic North Pole is to the west of the
geographic North Pole and a correction must be applied to a
compass indication to get a true direction.

The magnets align with the Earth’s magnetic field and the Figure 7-32. Isogonic lines are lines of equal variation.
pilot reads the direction on the scale opposite the lubber line.
Note that in Figure 7-31, the pilot sees the compass card from
its backside. When the pilot is flying north as the compass
shows, east is to the pilot’s right. On the card, “33”, which
represents 330° (west of north), is to the right of north. The
reason for this apparent backward graduation is that the card
remains stationary, and the compass housing and the pilot turn
around it, always viewing the card from its backside.

7-23

Flying in the Washington, D.C., area, for example, the variation Figure 7-34. A compass correction card shows the deviation
is 10° west. If a pilot wants to fly a true course of south (180°), correction for any heading.
the variation must be added to this, resulting in a magnetic course
of 190° to fly. Flying in the Los Angeles, California, area, the complete the compass coreection card. If the pilot wants to
variation is 14° east. To fly a true course of 180° there, the pilot fly a magnetic heading of 120° and the aircraft is operating
would have to subtract the variation and fly a magnetic course with the radios on, the pilot should fly a compass heading
of 166°. The variation error does not change with the heading of of 123°.
the aircraft; it is the same anywhere along the isogonic line.
The corrections for variation and deviation must be applied
Deviation in the correct sequence and is shown below, starting from
The magnets in a compass align with any magnetic field. the true course desired.
Local magnetic fields in an aircraft caused by electrical
current flowing in the structure, in nearby wiring or any Step 1: Determine the Magnetic Course
magnetized part of the structure, conflict with the Earth’s True Course (180°) ± Variation (+10°) = Magnetic Course (190°)
magnetic field and cause a compass error called deviation.
The magnetic course (190°) is steered if there is no deviation
Deviation, unlike variation, is different on each heading, error to be applied. The compass card must now be considered
but it is not affected by the geographic location. Variation for the compass course of 190°.
error cannot be reduced or changed, but deviation error can
be minimized when an AMT performs the maintenance task Step 2: Determine the Compass Course
known as “swinging the compass.” Magnetic Course (190°, from step 1) ± Deviation (–2°, from
correction card) = Compass Course (188°)
Most airports have a compass rose, which is a series of lines
marked out on a ramp or maintenance runup area where there
is no magnetic interference. Lines, oriented to magnetic north,
are painted every 30°, as shown in Figure 7-33.

True north

330 N NOTE: Intermediate magnetic courses between those listed
300 030 on the compass card need to be interpreted. Therefore, to
steer a true course of 180°, the pilot would follow a compass
W 060 course of 188°.

240 E To find the true course that is being flown when the compass
210 course is known:
120 Compass Course ± Deviation = Magnetic Course ± Variation=
S 150 True Course

Figure 7-33. Utilization of a compass rose aids compensation for Dip Errors
deviation errors.
The lines of magnetic flux are considered to leave the Earth
The AMT aligns the aircraft on each magnetic heading and at the magnetic North Pole and enter at the magnetic South
adjusts the compensating magnets to minimize the difference Pole. At both locations the lines are perpendicular to the
between the compass indication and the actual magnetic Earth’s surface. At the magnetic equator, which is halfway
heading of the aircraft. Any error that cannot be removed between the poles, the lines are parallel with the surface. The
is recorded on a compass correction card, like the one in magnets in a compass align with this field, and near the poles
Figure 7-34, and placed in a cardholder near the compass. The they dip, or tilt, the float and card. The float is balanced with
pilot can taxi the aircraft to the compass rose and maneuver a small dip-compensating weight, to dampen the effects of
the aircraft to the headings prescribed by the AMT, and if dip when operating in the middle latitudes of the northern
authorized to do so, the AMT can also taxi and maneuver the hemisphere. This dip (and weight) causes two very noticeable
aircraft; however, only the AMT can adjust the compass or errors: northerly turning error and acceleration error.

7-24

The pull of the vertical component of the Earth’s magnetic field When an aircraft is flying on a heading of south and begins
causes northerly turning error, which is apparent on a heading a turn toward east, the Earth’s magnetic field pulls on the
of north or south. When an aircraft flying on a heading of north end of the magnet that rotates the card toward east, the same
makes a turn toward east, the aircraft banks to the right, and direction the turn is being made. If the turn is made from
the compass card tilts to the right. The vertical component of south toward west, the magnetic pull starts the card rotating
the Earth’s magnetic field pulls the northseeking end of the toward west—again, in the same direction the turn is being
magnet to the right, and the float rotates, causing the card to made. The rule for this error is: when starting a turn from a
rotate toward west, the direction opposite the direction the turn southerly heading, the compass indication leads the turn.
is being made. [Figure 7-35]
In acceleration error, the dip-correction weight causes the end
If the turn is made from north to west, the aircraft banks to of the float and card marked N (the south-seeking end) to be
the left and the compass card tilts down on the left side. The heavier than the opposite end. When the aircraft is flying at
magnetic field pulls on the end of the magnet that causes the a constant speed on a heading of east or west, the float and
card to rotate toward east. This indication is again opposite to card is level. The effects of magnetic dip and the weight are
the direction the turn is being made. The rule for this error is: approximately equal. If the aircraft accelerates on a heading
when starting a turn from a northerly heading, the compass of east [Figure 7-36], the inertia of the weight holds its end of
indication lags behind the turn. the float back and the card rotates toward north. As soon as the

Figure 7-35. Northerly turning error.

Figure 7-36. Effects of acceleration error.

7-25

speed of the aircraft stabilizes, the card swings back to its east Lags or Leads
indication. If, while flying on this easterly heading, the aircraft
decelerates, the inertia causes the weight to move ahead and the When starting a turn from a northerly heading, the compass
card rotates toward south until the speed again stabilizes. lags behind the turn. When starting a turn from a southerly
heading, the compass leads the turn.

When flying on a heading of west, the same things happen. Eddy Current Damping
Inertia from acceleration causes the weight to lag, and the
card rotates toward north. When the aircraft decelerates on The decreased amplitude of oscillations by the interaction
a heading of west, inertia causes the weight to move ahead of magnetic fields. In the case of a vertical card magnetic
and the card rotates toward south. compass, flux from the oscillating permanent magnet
produces eddy currents in a damping disk or cup. The
A mnemonic, or memory jogger, for the effect of acceleration magnetic flux produced by the eddy currents opposes the flux
error is the word “ANDS” (acceleration—north, deceleration— from the permanent magnet and decreases the oscillations.
south). Acceleration causes an indication toward north;
deceleration causes an indication toward south. Outside Air Temperature (OAT) Gauge

Oscillation Error The outside air temperature (OAT) gauge is a simple and
Oscillation is a combination of all of the other errors, and it effective device mounted so that the sensing element is
results in the compass card swinging back and forth around exposed to the outside air. The sensing element consists
the heading being flown. When setting the gyroscopic of a bimetallic-type thermometer in which two dissimilar
heading indicator to agree with the magnetic compass, use materials are welded together in a single strip and twisted
the average indication between the swings. into a helix. One end is anchored into protective tube and the
other end is affixed to the pointer, which reads against the
The Vertical Card Magnetic Compass calibration on a circular face. OAT gauges are calibrated in
The floating magnet type of compass not only has all the errors degrees °C, °F, or both. An accurate air temperature provides
just described, but also lends itself to confused reading. It is the pilot with useful information about temperature lapse rate
easy to begin a turn in the wrong direction because its card with altitude chaOnugtes.id[eFaigirutreem7p-e3r8a]ture gauge
appears backward. East is on what the pilot would expect to be
the west side. The vertical card magnetic compass eliminates 20 40
some of the errors and confusion. The dial of this compass 60
is graduated with letters representing the cardinal directions, 0
numbers every 30°, and tick marks every 5°. The dial is rotated -20 0
by a set of gears from the shaft-mounted magnet, and the nose 20 80
of the symbolic aircraft on the instrument glass represents the -20
lubber line for reading the heading of the aircraft from the dial. -40 40 100
Eddy currents induced into an aluminum-damping cup damp,
or decrease, oscillatVioenrtoicfatlhcearmdacgonmept.a[sFsigure 7-37] -40 C 60 120

-60 F 140

33 N 3 Figure 7-38. Outside air temperature (OAT) gauge.

24 W 30 6 E 12 Chapter Summary

15 S 21 Flight instruments enable an aircraft to be operated with
maximum performance and enhanced safety, especially when
flying long distances. Manufacturers provide the necessary
flight instruments, but to use them effectively, pilots need
to understand how they operate. As a pilot, it is important to
become very familiar with the operational aspects of the pitot-
static system and associated instruments, the vacuum system
and associated instruments, the gyroscopic instruments, and
the magnetic compass.

Figure 7-37. Vertical card compass.
7-26

FlightChapter8 Manuals and
Other Documents

Introduction

Each aircraft comes with documentation and a set of manuals
with which a pilot must be familiar in order to fly that aircraft.
This chapter covers airplane flight manuals (AFM), the
pilot’s operating handbook (POH), and aircraft documents
pertaining to ownership, airworthiness, maintenance, and
operations with inoperative equipment. Knowledge of these
required documents and manuals is essential for a pilot to
conduct a safe flight.

Airplane Flight Manuals (AFM)

Flight manuals and operating handbooks are concise reference
books that provide specific information about a particular
aircraft or subject. They contain basic facts, information,
and/or instructions for the pilot about the operation of an
aircraft, flying techniques, etc., and are intended to be kept
at hand for ready reference.

8-1

The aircraft owner/information manual is a document Most manufacturers include a table of contents, which
developed by the manufacturer and contains general identifies the order of the entire manual by section number
information about the make and model of aircraft. The and title. Usually, each section also contains a table of
manual is not pproved by the Federal Aviation Administration contents for that section. Page numbers reflect the section
(FAA) and is not specific to an individual aircraft. The and page within that section (1-1, 1-2, 2-1, 3-1, etc.). If the
manual provides general information about the operation of manual is published in loose-leaf form, each section is usually
an aircraft, is not kept current, and cannot be substituted for marked with a divider tab indicating the section number or
the AFM/POH. title, or both. The Emergency Procedures section may have
a red tab for quick identification and reference.
An AFM is a document developed by the manufacturer and
approved by the FAA. This book contains the information General (Section 1)
and instructions required to operate an aircraft safely. A The General section provides the basic descriptive
pilot must comply with this information which is specific information on the airframe and powerplant(s). Some
to a particular make and model aircraft, usually by serial manuals include a three-dimensional drawing of the aircraft
number. An AFM contains the operating procedures and that provides dimensions of various components. Included
limitations of that aircraft. Title 14 of the Code of Federal are such items as wingspan, maximum height, overall length,
Regulations (14 CFR) part 91 requires that pilots comply wheelbase length, main landing gear track width, diameter
with the operating limitations specified in the approved flight of the rotor system, maximum propeller diameter, propeller
manuals, markings, and placards. ground clearance, minimum turning radius, and wing area.
This section serves as a quick reference and helps a pilot
Originally, flight manuals followed whatever format and become familiar with the aircraft.
content the manufacturer felt was appropriate, but this
changed with the acceptance of Specification No. 1 prepared The last segment of the General section contains definitions,
by the General Aviation Manufacturers Association (GAMA). abbreviations, explanations of symbology, and some of
Specification No. 1 established a standardized format for all the terminology used in the POH. At the option of the
general aviation airplane and helicopter flight manuals. manufacturer, metric and other conversion tables may also
be included.
The POH is a document developed by the aircraft manufacturer
and contains FAA approved AFM information. If “POH” is Limitations (Section 2)
used in the main title, a statement must be included on the The Limitations section contains only those limitations required
title page indicating that sections of the document are FAA by regulation or that are necessary for the safe operation of
approved as the AFM. the aircraft, powerplant, systems, and equipment. It includes
operating limitations, instrument markings, color-coding, and
The POH for most light aircraft built after 1975 is also basic placards. Some of the limitation areas are: airspeed,
designated as the FAA-approved flight manual. The typical powerplant, weight and loading distribution, and flight.
AFM/POH contains the following nine sections: General;
Limitations; Emergency Procedures; Normal Procedures; Airspeed
Performance; Weight and Balance/Equipment List; Systems Airspeed limitations are shown on the airspeed indicator
Description; Handling, Service, and Maintenance; and (ASI) by color coding and on placards or graphs in the aircraft.
Supplements. Manufacturers also have the option of including [Figure 8-1] A red line on the ASI shows the airspeed limit
additional sections, such as one on Safety and Operational beyond which structural damage could occur. This is called the
Tips or an alphabetical index at the end of the POH. never-exceed speed (VNE). A yellow arc indicates the speed
range between maximum structural cruising speed (VNO) and
Preliminary Pages VNE. Operation of an airplane in the yellow airspeed arc is
While the AFM/POH may appear similar for the same make for smooth air only, and then only with caution. A green arc
and model of aircraft, each manual is unique and contains depicts the normal operating speed range, with the upper end
specific information about a particular aircraft, such as the at VNO, and the lower end at stalling speed at maximum weight
equipment installed and weight and balance information. with the landing gear and flaps retracted (VS1). For airplanes
Manufacturers are required to include the serial number and the flap operating range is depicted by the white arc, with the
registration on the title page to identify the aircraft to which upper end at the maximum flap extended speed (VFE), and
the manual belongs. If a manual does not indicate a specific the lower end at the stalling speed with the landing gear and
aircraft registration and serial number, it is limited to general flaps in the landing configuration (VSO).
study purposes only.

8-2

Single-Engine Airspeed Indicator Oil Gauge

245 II5 Maximum
Normal operating range
T 200 6I00200SPI P Minimum
E °F I50 R
M I00 E
P S
S

75 OIL 0

Figure 8-1. Single-engine airpseed indicator. Figure 8-3. Minimum, maximum, and normal operating range
markings on oil gauge.
In addition to the markings listed above, small multi-engine
airplanes will have a red radial line to indicate single-engine a red radial line and the normal operating range with a green
minimum controllable airspeed (VMC). A blue radial line arc. [Figure 8-4] Some instruments may have a yellow arc
is used to indicate single-engine best rate of climb speed at to indicate a caution area.
maximum weight at sea level (VYSE). [Figure 8-2]
Weight and Loading Distribution
Multiengine Airspeed Indicator Weight and Loading Distribution contains the maximum
certificated weights, as well as the center of gravity (CG)
IAS range. The location of the reference datum used in balance
computations is included in this section. Weight and balance
260 40 computations are not provided in this area, but rather in the
AIRSPEED weight and balance section of the AFM/POH.
KNOTS
200 250 60 Manifold Pressure Gauge

180 200 160 80 25 30 35
140 MANIFOLD
160 TAS
140 100 20 PRESSURE 40

120

Figure 8-2. Multi-engine airpseed indicator. 15 45IN Hg
ALg.
10 50

Powerplant Engine rpm is indicated on the tachometer
The Powerplant Limitations portion describes operating
limitations on an aircraft’s reciprocating or turbine engine(s). I5 20
These include limitations for takeoff power, maximum I0 25RPM
continuous power, and maximum normal operating power,
which is the maximum power the engine can produce without HUNDREDS
any restrictions and is depicted by a green arc. Other items
that can be included in this area are the minimum and 5 30I
maximum oil and fuel pressures, oil and fuel grades, and 3
propeller operating limits. [Figure 8-3] I0

All reciprocating-engine powered aircraft must have a HOURS 35
revolutions per minute (rpm) indicator for each engine. AVOID
Aircraft equipped with a constant-speed propeller or rotor CONTINUOUS
system use a manifold pressure gauge to monitor power OPERATION
output and a tachometer to monitor propeller or rotor speed. BETWEEN 2250
Both instruments depict the maximum operating limit with AND 2350 RPM

Figure 8-4. Manifold pressure gauge (top) and tachometer
(bottom).

8-3

Flight Limits recommended procedures for handling malfunctions that are
Flight Limits list authorized maneuvers with appropriate not considered emergencies.
entry speeds, flight load factor limits, and kinds of operation
limits. It also indicates those maneuvers that are prohibited, Normal Procedures (Section 4)
such as spins or acrobatic flight, as well as operational This section begins with a list of the airspeeds for normal
limitations such as flight into known icing conditions. operations. The next area consists of several checklists that
may include preflight inspection, before starting procedures,
Placards starting engine, before taxiing, taxiing, before takeoff, climb,
Most aircraft display one or more placards that contain cruise, descent, before landing, balked landing, after landing,
information having a direct bearing on the safe operation of and post flight procedures. An Amplified Procedures area
the aircraft. These placards are located in conspicuous places follows the checklists to provide more detailed information
and are reproduced in the Limitations section or as directed about the various previously mentioned procedures.
by an Airworthiness Directive (AD). [Figure 8-5]
To avoid missing important steps, always use the appropriate
checklists when available. Consistent adherence to approved
checklists is a sign of a disciplined and competent pilot.

Performance (Section 5)
The Performance section contains all the information required
by the aircraft certification regulations, and any additional
performance information the manufacturer deems important to
pilot ability to safely operate the aircraft. Performance charts,
tables, and graphs vary in style, but all contain the same basic
information. Examples of the performance information found
in most flight manuals include a graph or table for converting
calibrated airspeed to true airspeed; stall speeds in various
configurations; and data for determining takeoff and climb
performance, cruise performance, and landing performance.
Figure 8-6 is an example of a typical performance graph. For
more information on use of the charts, graphs, and tables,
refer to Chapter 10, Aircraft Performance.

Figure 8-5. Placards are used to depict aircraft limitations. Weight and Balance/Equipment List (Section 6)
The Weight and Balance/Equipment List section contains all
Emergency Procedures (Section 3) the information required by the FAA to calculate the weight
Checklists describing the recommended procedures and and balance of an aircraft. Manufacturers include sample
airspeeds for coping with various types of emergencies or weight and balance problems. Weight and balance is discussed
critical situations are located in the Emergency Procedures in greater detail in Chapter 9, Weight and Balance.
section. Some of the emergencies covered include:
engine failure, fire, and system failure. The procedures Systems Description (Section 7)
for inflight engine restarting and ditching may also be This section describes the aircraft systems in a manner
included. Manufacturers may first show an emergency appropriate to the pilot most likely to operate the aircraft.
checklist in an abbreviated form, with the order of items For example, a manufacturer might assume an experienced
reflecting the sequence of action. Amplified checklists that pilot will be reading the information for an advanced aircraft.
provide additional information on the procedures follow For more information on aircraft systems, refer to Chapter
the abbreviated checklist. To be prepared for emergency 6, Aircraft Systems.
situations, memorize the immediate action items and, after
completion, refer to the appropriate checklist. Handling, Service, and Maintenance (Section 8)
The Handling, Service, and Maintenance section describes
Manufacturers may include an optional subsection the maintenance and inspections recommended by the
titled “Abnormal Procedures.” This subsection describes manufacturer (and the regulations). Additional maintenance or
inspections may be required by the issuance of AD applicable
to the airframe, engine, propeller, or components.

8-4

Stall Speed

EXAMPLE Gross weight: 2,170 pounds Calibrated stall speed 70
Angle of bank: 20° Indicated stall speed 60
Flap position: 40° 50
Stall speed, indicated: 44 knots 40
30
Maximum weight - 2,440 (pounds) 0° Flaps Stall speed (knots)

0° Flaps 40° Flaps
40° Flaps

2,400 2,200 2,000 1,800 1,600 0° 20° 40° 60°
Angle of bank (degrees)
Gross weight (pounds)

Figure 8-6. Stall speed chart.

This section also describes preventive maintenance that
may be accomplished by certificated pilots, as well as the
manufacturer’s recommended ground handling procedures. It
includes considerations for hangaring, tie-down, and general
storage procedures for the aircraft.

Supplements (Section 9) Figure 8-7. Supplements provide information on optional
The Supplements section contains information necessary equipment.
to safely and efficiently operate the aircraft when equipped
with optional systems and equipment (not provided with the
standard aircraft). Some of this information may be supplied
by the aircraft manufacturer or by the manufacturer of the
optional equipment. The appropriate information is inserted
into the flight manual at the time the equipment is installed.
Autopilots, navigation systems, and air-conditioning
systems are examples of equipment described in this section.
[Figure 8-7]

Safety Tips (Section 10)
The Safety Tips section is an optional section containing a
review of information that enhances the safe operation of the
aircraft. For example, physiological factors, general weather
information, fuel conservation procedures, high altitude
operations, or cold weather operations might be discussed.

8-5

Aircraft Documents For additional information, see 14 CFR section 47.41. When
one of the events listed in 14 CFR section 47.41 occurs, the
Certificate of Aircraft Registration previous owner must notify the FAA by filling in the back of
Before an aircraft can be flown legally, it must be registered the Certificate of Aircraft Registration, and mailing it to:
with the FAA Aircraft Registry. The Certificate of Aircraft
Registration, which is issued to the owner as evidence of FAA Aircraft Registration Branch, AFS-750
the registration, must be carried in the aircraft at all times. P.O. Box 25504
[Figure 8-8] Oklahoma City, OK 73125-0504

The Certificate of Aircraft Registration cannot be used for A dealer’s aircraft registration certificate is another form of
operations when: registration certificate, but is valid only for required flight
tests by the manufacturer or in flights that are necessary for
• The aircraft is registered under the laws of a foreign the sale of the aircraft by the manufacturer or a dealer. The
country. dealer must remove the certificate when the aircraft is sold.

• The aircraft’s registration is canceled upon written Upon complying with 14 CFR section 47.31, the pink
request of the certificate holder. copy of the application for an Aircraft Registration
Application, Aeronautical Center (AC) Form 8050-1,
• The aircraft is totally destroyed or scrapped. provides authorization to operate an unregistered aircraft
for a period not to exceed 90 days. Since the aircraft is
• The ownership of the aircraft is transferred.

• The certificate holder loses United States
citizenship.

Figure 8-8. AC Form 8050-3, Certificate of Aircraft Registration.
8-6

unregistered, it cannot be operated outside of the United If evidence of ownership can not be supplied, an affidavit
States until a permanent Certificate of Aircraft Registration stating why it is not available must be submitted on the AC
is received and placed in the aircraft. Form 8050-88A.

The FAA does not issue any certificate of ownership or If an owner wants to register a newly manufactured LSA
endorse any information with respect to ownership on a that will be certificated as an experimental light sport aircraft
Certificate of Aircraft Registration. under 14 CFR section 21.191(i)(2), the following items must
be provided: AC Form 8050-88A or its equivalent (completed
NOTE: For additional information concerning the Aircraft by the LSA manufacturer, unless previously submitted
Registration Application or the Aircraft Bill of Sale, contact to the Registry by the manufacturer), evidence from the
the nearest FAA Flight Standards District Office (FSDO). manufacturer of ownership of an aircraft (kit-built or fly-
away), AC Form 8050-1, and a $5.00 registration fee.
Light Sport Aircraft (LSA)
The FAA recently added a new category called Light Sport Airworthiness Certificate
Aircraft (LSA). Requirements for registration of these An Airworthiness Certificate is issued by a representative
aircraft differ from those of other aircraft. The following of the FAA after the aircraft has been inspected, is found to
guidelines are provided for LSA registration, but a more meet the requirements of 14 CFR part 21, and is in condition
detailed explanation can be found on the FAA website at for safe operation. The Airworthiness Certificate must be
http//www.faa.gov. displayed in the aircraft so it is legible to the passengers and
crew whenever it is operated. The Airworthiness Certificate
An existing LSA that has not been issued a United States is transferred with the aircraft except when it is sold to a
or foreign airworthiness certificate, and does not meet the foreign purchaser.
provisions of 14 CFR section 103.1, must meet specific
criteria in order to be certificated as an experimental LSA A Standard Airworthiness Certificate is issued for
under 14 CFR section 21.191 (i)(l) before January 31, 2008. aircraft type certificated in the normal, utility, acrobatic,
The following items must be provided: evidence of ownership commuter, transport categories, and manned free balloons.
of the parts or the manufacturer’s kit, Aircraft Registration Figure 8-9 illustrates a Standard Airworthiness Certificate,
Application (AC Form 8050-1), and a $5.00 registration fee. and an explanation of each item in the certificate follows.

Figure 8-9. FAA Form 8100-2, Standard Airworthiness Certificate.

8-7

1. Nationality and Registration Marks. The “N” Aircraft Maintenance
indicates the aircraft is registered in the United States. Maintenance is defined as the preservation, inspection,
Registration marks consist of a series of up to five overhaul, and repair of an aircraft, including the replacement
numbers or numbers and letters. In this case, N2631A of parts. Regular and proper maintenance ensures that
is the registration number assigned to this airplane. an aircraft meets an acceptable standard of airworthiness
throughout its operational life.
2. Manufacturer and Model. Indicates the manufacturer,
make, and model of the aircraft. Although maintenance requirements vary for different
types of aircraft, experience shows that aircraft need some
3. Aircraft Serial Number. Indicates the manufacturer’s type of preventive maintenance every 25 hours of flying
serial number assigned to the aircraft, as noted on the time or less, and minor maintenance at least every 100
aircraft data plate. hours. This is influenced by the kind of operation, climatic
conditions, storage facilities, age, and construction of the
4. Category. Indicates the category in which the aircraft aircraft. Manufacturers supply maintenance manuals, parts
must be operated. In this case, it must be operated catalogs, and other service information that should be used
in accordance with the limitations specified for the in maintaining the aircraft.
“NORMAL” category.
Aircraft Inspections
5. Authority and Basis for Issuance. Indicates the aircraft
conforms to its type certificate and is considered in 14 CFR part 91 places primary responsibility on the owner or
condition for safe operation at the time of inspection operator for maintaining an aircraft in an airworthy condition.
and issuance of the certificate. Any exemptions from Certain inspections must be performed on the aircraft, and
the applicable airworthiness standards are briefly the owner must maintain the airworthiness of the aircraft
noted here and the exemption number given. The word during the time between required inspections by having any
“NONE” is entered if no exemption exists. defects corrected.

6. Terms and Conditions. Indicates the Airworthiness 14 CFR part 91, subpart E, requires the inspection of all civil
Certificate is in effect indefinitely if the aircraft is aircraft at specific intervals to determine the overall condition.
maintained in accordance with 14 CFR parts 21, 43, The interval depends upon the type of operations in which the
and 91, and the aircraft is registered in the United aircraft is engaged. All aircraft need to be inspected at least
States. once each 12 calendar months, while inspection is required
for others after each 100 hours of operation. Some aircraft
Also included are the date the certificate was issued are inspected in accordance with an inspection system set up
and the signature and office identification of the FAA to provide for total inspection of the aircraft on the basis of
representative. calendar time, time in service, number of system operations,
or any combination of these.
A Standard Airworthiness Certificate remains in effect
if the aircraft receives the required maintenance and is All inspections should follow the current manufacturer’s
properly registered in the United States. Flight safety relies maintenance manual, including the Instructions for
in part on the condition of the aircraft, which is determined Continued Airworthiness concerning inspections intervals,
by inspections performed by mechanics, approved repair parts replacement, and life-limited items as applicable to
stations, or manufacturers that meet specific requirements the aircraft.
of 14 CFR part 43.
Annual Inspection
A Special Airworthiness Certificate is issued for all aircraft Any reciprocating engine or single-engine turbojet/
certificated in other than the Standard classifications, such turbopropeller-powered small aircraft (12,500 pounds and
as Experimental, Restricted, Limited, Provisional, and LSA. under) flown for business or pleasure and not flown for
LSA receive a pink special airworthiness certificate. There compensation or hire is required to be inspected at least
are exceptions. For example, the Piper Cub is in the new LSA annually. The inspection shall be performed by a certificated
category, but it was certificated as a normal aircraft during airframe and powerplant (A&P) mechanic who holds an
its manufacture. When purchasing an aircraft classified as inspection authorization (IA) by the manufacturer of the
other than Standard, it is recommended that the local FSDO
be contacted for an explanation of the pertinent airworthiness
requirements and the limitations of such a certificate.

8-8

aircraft or by a certificated and appropriately rated repair Emergency Locator Transmitter
station. The aircraft may not be operated unless the annual An emergency locator transmitter (ELT) is required by 14
inspection has been performed within the preceding 12 CFR section 91.207 and must be inspected within 12 calendar
calendar months. A period of 12 calendar months extends months after the last inspection for the following:
from any day of a month to the last day of the same month the
following year. An aircraft overdue for an annual inspection • Proper installation
may be operated under a Special Flight Permit issued by
the FAA for the purpose of flying the aircraft to a location • Battery corrosion
where the annual inspection can be performed. However, all
applicable ADs that are due must be complied with before • Operation of the controls and crash sensor
the flight.
• The presence of a sufficient signal radiated from its
antenna

100-Hour Inspection The ELT must be attached to the airplane in such a manner
All aircraft under 12,500 pounds (except turbojet/ that the probablity of damage to the transmitter in the event
turbopropeller-powered multi-engine airplanes and turbine of crash impact is minimized. Fixed and deployable automatic
powered rotorcraft), used to carry passengers for hire, must type transmitters must be attached to the airplane as far aft
have received a 100-hour inspection within the preceding 100 as practicable. Batteries used in the ELTs must be replaced
hours of time in service and have been approved for return to (or recharged, if the batteries are rechargeable):
service. Additionally, an aircraft used for flight instruction
for hire, when provided by the person giving the flight • When the transmitter has been in use for more than 1
instruction, must also have received a 100-hour inspection. cumulative hour.
This inspection must be performed by an FAA-certificated
A&P mechanic, an appropriately rated FAA-certificated repair • When 50 percent of the battery useful life (or, for
station, or by the aircraft manufacturer. An annual inspection, rechargeable batteries, 50 percent of useful life of the
or an inspection for the issuance of an Airworthiness charge) has expired.
Certificate may be substituted for a required 100-hour
inspection. The 100-hour limitation may be exceeded by not An expiration date for replacing (or recharging) the battery
more than 10 hours while en route to reach a place where must be legibly marked on the outside of the transmitter
the inspection can be done. The excess time used to reach a and entered in the aircraft maintenance record. This does
place where the inspection can be done must be included in not apply to batteries that are essentially unaffected during
computing the next 100 hours of time in service. storage intervals, such as water-activated batteries.

Other Inspection Programs Preflight Inspections
The annual and 100-hour inspection requirements do not The preflight inspection is a thorough and systematic means
apply to large (over 12,500 pounds) airplanes, turbojets, or by which a pilot determines if the aircraft is airworthy and in
turbopropeller-powered multi-engine airplanes or to aircraft condition for safe operation. POHs and owner/information
for which the owner complies with a progressive inspection manuals contain a section devoted to a systematic method
program. Details of these requirements may be determined of performing a preflight inspection.
by reference to 14 CFR section 43.11 and 14 CFR part 91,
subpart E, and by inquiring at a local FSDO. Minimum Equipment Lists (MEL) and
Operations With Inoperative Equipment
Altimeter System Inspection
14 CFR section 91.411 requires that the altimeter, encoding 14 CFR requires that all aircraft instruments and installed
altimeter, and related system be tested and inspected in the equipment be operative prior to each departure. When the
preceding 24 months before operated in controlled airspace FAA adopted the minimum equipment list (MEL) concept
under instrument flight rules (IFR). for 14 CFR part 91 operations, this allowed operations with
inoperative equipment determined to be nonessential for safe
Transponder Inspection flight. At the same time, it allowed part 91 operators, without
14 CFR section 91.413 requires that before a transponder can an MEL, to defer repairs on nonessential equipment within
be used under 14 CFR section 91.215(a), it shall be tested the guidelines of part 91.
and inspected within the preceding 24 months.

8-9

The FAA has two acceptable methods of deferring The use of an MEL for an aircraft operated under 14
maintenance on small rotorcraft, non-turbine powered CFR part 91 also allows for the deferral of inoperative
airplanes, gliders, or lighter-than-air aircraft operated under items or equipment. The primary guidance becomes the
part 91. They are the deferral provision of 14 CFR section FAA-approved MEL issued to that specific operator and
91.213(d) and an FAA-approved MEL. N-numbered aircraft.

The deferral provision of 14 CFR section 91.213(d) is The FAA has developed master minimum equipment lists
widely used by most pilot/operators. Its popularity is due (MMELs) for aircraft in current use. Upon written request by
to simplicity and minimal paperwork. When inoperative an operator, the local FSDO may issue the appropriate make
equipment is found during preflight or prior to departure, the and model MMEL, along with an LOA, and the preamble.
decision should be to cancel the flight, obtain maintenance The operator then develops operations and maintenance
prior to flight, or to defer the item or equipment. (O&M) procedures from the MMEL. This MMEL with O&M
procedures now becomes the operator’s MEL. The MEL,
Maintenance deferrals are not used for inflight discrepancies. LOA, preamble, and procedures document developed by the
The manufacturer’s AFM/POH procedures are to be used in operator must be on board the aircraft when it is operated.
those situations. The discussion that follows assumes that The FAA considers an approved MEL to be a supplemental
the pilot wishes to defer maintenance that would ordinarily type certificate (STC) issued to an aircraft by serial number
be required prior to flight. and registration number. It, therefore, becomes the authority
to operate that aircraft in a condition other than originally
Using the deferral provision of 14 CFR section 91.213(d), type certificated.
the pilot determines whether the inoperative equipment is
required by type design, 14 CFR, or ADs. If the inoperative With an approved MEL, if the position lights were discovered
item is not required, and the aircraft can be safely operated inoperative prior to a daytime flight, the pilot would make
without it, the deferral may be made. The inoperative item an entry in the maintenance record or discrepancy record
shall be deactivated or removed and an INOPERATIVE provided for that purpose. The item is then either repaired or
placard placed near the appropriate switch, control, or deferred in accordance with the MEL. Upon confirming that
indicator. If deactivation or removal involves maintenance daytime flight with inoperative position lights is acceptable in
(removal always will), it must be accomplished by certificated accordance with the provisions of the MEL, the pilot would
maintenance personnel and recorded in accordance with 14 leave the position lights switch OFF, open the circuit breaker
CFR part 43. (or whatever action is called for in the procedures document),
and placard the position light switch as INOPERATIVE.
For example, if the position lights (installed equipment)
were discovered to be inoperative prior to a daytime flight, There are exceptions to the use of the MEL for deferral. For
the pilot would follow the requirements of 14 CFR section example, should a component fail that is not listed in the MEL
91.213(d). as deferrable (the tachometer, flaps, or stall warning device,
for example), then repairs are required to be performed prior
The deactivation may be a process as simple as the pilot to departure. If maintenance or parts are not readily available
positioning a circuit breaker to the OFF position, or as at that location, a special flight permit can be obtained from
complex as rendering instruments or equipment totally the nearest FSDO. This permit allows the aircraft to be
inoperable. Complex maintenance tasks require a certificated flown to another location for maintenance. This allows an
and appropriately rated maintenance person to perform the aircraft that may not currently meet applicable airworthiness
deactivation. In all cases, the item or equipment must be requirements, but is capable of safe flight, to be operated
placarded INOPERATIVE. under the restrictive special terms and conditions attached
to the special flight permit.
All small rotorcraft, non-turbine powered airplanes, gliders,
or lighter-than-air aircraft operated under 14 CFR part 91 Deferral of maintenance is not to be taken lightly,
are eligible to use the maintenance deferral provisions of 14 and due consideration should be given to the effect an
CFR section 91.213(d). However, once an operator requests inoperative component may have on the operation of an
an MEL, and a Letter of Authorization (LOA) is issued by the aircraft, particularly if other items are inoperative. Further
FAA, then the use of the MEL becomes mandatory for that information regarding MELs and operations with inoperative
aircraft. All maintenance deferrals must be accomplished in equipment can be found in AC 91-67, Minimum Equipment
accordance with the terms and conditions of the MEL and Requirements for General Aviation Operations Under CFR
the operator-generated procedures document. Part 91.

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Preventive Maintenance of any primary structure or operating system or
interfere with an operating system or affect the primary
Preventive maintenance is considered to be simple or minor structure of the aircraft; making small, simple repairs
preservation operations and the replacement of small standard to fairings, nonstructural cover plates, cowlings, and
parts, not involving complex assembly operations. Allowed small patches and reinforcements not changing the
items of preventative maintenance are listed and limited to contour to interfere with proper air flow; replacing
the items of 14 CFR part 43, appendix A(c). side windows where that work does not interfere with
the structure or any operating system such as controls,
Maintenance Entries electrical equipment, etc.
All pilots who maintain or perform preventive maintenance
must make an entry in the maintenance record of the aircraft. • Replacing safety belts, seats or seat parts with
The entry must include: replacement parts approved for the aircraft, not
involving disassembly of any primary structure or
1. A description of the work, such as “changed oil (Shell operating system, bulbs, reflectors, and lenses of
Aero-50) at 2,345 hours.” position and landing lights.

2. The date of completion of the work performed. • Replacing wheels and skis where no weight-and-
balance computation is involved; replacing any
3. The entry of the pilot’s name, signature, certificate cowling not requiring removal of the propeller or
number, and type of certificate held. disconnection of flight controls; replacing or cleaning
spark plugs and setting of spark plug gap clearance;
Examples of Preventive Maintenance replacing any hose connection, except hydraulic
The following examples of preventive maintenance are taken connections; however, prefabricated fuel lines may
from 14 CFR Part 43, Maintenance, Preventive Maintenance, be replaced.
Rebuilding, and Alternation, which should be consulted for
a more in-depth look at preventive maintenance a pilot can • Cleaning or replacing fuel and oil strainers or filter
perform on an aircraft. Remember, preventive maintenance elements; servicing batteries, cleaning of balloon
is limited to work that does not involve complex assembly burner pilot and main nozzles in accordance with the
operations and includes: balloon manufacturer’s instructions.

• Removal, installation, and repair of landing gear • The interchange of balloon baskets and burners on
tires and shock cords; servicing landing gear shock envelopes when the basket or burner is designated as
struts by adding oil, air, or both; servicing gear wheel interchangeable in the balloon type certificate data
bearings; replacing defective safety wiring or cotter and the baskets and burners are specifically designed
keys; lubrication not requiring disassembly other than for quick removal and installation; adjustment
removal of nonstructural items such as cover plates, of nonstructural standard fasteners incidental to
cowlings, and fairings; making simple fabric patches operations.
not requiring rib stitching or the removal of structural
parts or control surfaces. In the case of balloons, • The installations of anti-misfueling devices to reduce
the making of small fabric repairs to envelopes the diameter of fuel tank filler openings only if the
(as defined in, and in accordance with, the balloon specific device has been made a part of the aircraft type
manufacturer’s instructions) not requiring load tape certificate data by the aircraft manufacturer, the aircraft
repair or replacement. manufacturer has provided FAA-approved instructions
for installation of the specific device, and installation
• Replenishing hydraulic fluid in the hydraulic reservoir; does not involve the disassembly of the existing tank
refinishing decorative coating of fuselage, balloon filler opening; troubleshooting and repairing broken
baskets, wings, tail group surfaces (excluding balanced circuits in landing light wiring circuits.
control surfaces), fairings, cowlings, landing gear, cabin,
or flight deck interior when removal or disassembly • Removingandreplacingself-contained,frontinstrument
of any primary structure or operating system is not panel-mounted navigation and communication devices
required; applying preservative or protective material employing tray-mounted connectors that connect the
to components where no disassembly of any primary unit when the unit is installed into the instrument
structure or operating system is involved and where panel; excluding automatic flight control systems,
such coating is not prohibited or is not contrary to transponders, and microwave frequency distance
good practices; repairing upholstery and decorative measuring equipment (DME). The approved unit must
furnishings of the cabin, flight deck, or balloon basket be designed to be readily and repeatedly removed and
interior when the repair does not require disassembly replaced, and pertinent instructions must be provided.

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