6 - Aircraft Instruments and Systems Flashcards

Question 1

Q

Pressure Flight Instruments

What are the pressure flight instruments, and how do they work?

Answer

A

The pressure flight instruments are

Airspeed indicator (ASI)/Mach meter (MM)
Altimeter
Vertical speed indicator (VSl)

Pressure instruments measure atmospheric pressure by using the
pitot-static system, which is a combined sensor system that detects the
following:

The total pressure - (static and dynamic pressure), also called pitot
pressure, which is measured by a pi tot probe
Static pressure - alone, which is measured by either the static port
on a pitot probe or by a separate static vent

The difference between the two will give a measurement of the dynamic
pressure. That is,

Dynamic pressure = total pressure - static pressure

Dynamic and/or static pressure measurements are the basis of the
flight instrument readings.

Question 2

Q

Pressure Flight Instruments

How does the airspeed indicator (ASI) work?

Answer

A

The ASI measures dynamic pressure as the difference between the total pitot pressure measured in the instrument’s capsule/diaphragm
and the static pressure measured in the case.

The dynamic pressure represents the indicated airspeed (lAS) as knots per hour.

(See Q: Describe indicated airspeed (lAS), page 120.)

The ASI instrument is calibrated to international standard atmosphere (ISA) mean sea level (MSL) density of 1225 g/mJ.

Question 3

Q

Pressure Flight Instruments

What are the airspeed indicator (ASI) instrument errors?

Answer

A

The ASI instrument suffers from the following errors:

Instrument error
Pressure error
Density error
Compressibility error
Maneuver error
Blocked pitot static system

Question 4

Q

Pressure Flight Instruments

How is VMO displayed on the airspeed indicator (ASI)?

Answer

A

On the ASI display, a red/black striped pointer indicates the VMO speed.

Question 5

Q

Pressure Flight Instruments

Describe how a Mach meter works.

Answer

A

The Mach meter measures the airspeed relative to the local speed of sound.

In essence, the Mach meter is a combined airspeed indicator (ASI) and
altimeter that comprises the following:

A capsule feed with pitot pressure inside an ambient static pressure
feed case that acts as anASI and measures dynamic pressure as the
airspeed.
A sealed capsule containing international standard atmosphere (ISA)
mean sea level (MSL) conditions inside the ambient static pressure
feed case, which acts as an altimeter by measuring the static
pressure, which it relates to an altitude.

Mach meter ratio = (pitot-static)/static

These two functions inside the Mach meter are linked via a ratio arm
that itself acts on a ranging arm to ultimately move the pointer/digital

Question 6

Q

Pressure Flight Instruments

What errors does a Mach meter suffer from?

Answer

A

The Mach meter only suffers from the following errors:

Instrument error, which is caused by the inaccuracies in the Mach
meter’s construction
Pressure error, also known as position or configuration error
However, these errors are extremely small, and therefore, the
indicated Mach number speed can be read as the true Mach number
speed.
Blocked pitot static system (see Q: What are the airspeed indicator
(ASI) / Mach number (Mn) indications and actions for a blocked pitot
static probe? page 129).

Note: The Mach meter does not suffer from density or temperature
errors because its built-in altitude capsule design and its ratio to the
dynamic pressure measured compensate for density and temperature
variations.

Question 7

Q

Pressure Flight Instruments

What are the airspeed indicator (ASI)/Mach meter indications and actions
for a blocked pitot and/or static probe?

Answer

A

A static line blockage means that the static pressure in the ASI/Mach
meter instrument case remains a constant value. Therefore,

At a constant altitude, the ASI/MM will read correctly.
During descent, the ASI/MM will over-read due to an increase in the
pitot pressure in the capsule against the trapped low static pressure
of the higher altitude.
During climb, the ASI/MM will under-read due to a decrease in the
pitot pressure in the capsule against the trapped high static pressure
of the low altitude.

A pitot line blockage means that the total pressure in the ASIIMM
instrument capsule remains a constant value. Therefore,

At a constant altitude, the ASIIMM reading will not change even if
the airspeed does due to the trapped pitot pressure in the capsule
against a constant altitude static pressure.
During descent, the ASI/MM will under-read due to an increase in
the static pressure in the case against a constant pitot pressure.
During climb, the ASI/MM will over-read due to a decrease in the
static pressure in the case against a constant pitot pressure.

The actions for a blocked pitot/static system causing an unreliable
ASl/MM reading would be to
1. Ensure that the pitot static probe anti-ice heating (pitot heat) is on,
if applicable.
2. Use an alternative, such as a static source or an air data computer,
if applicable.
3. Use a limited flight panel, i.e., standby ASI.
4. Fly at a correct attitude and power setting.

Question 8

Q

Pressure Flight Instruments

How does a pressure altimeter work?

Answer

A

A simple pressure altimeter is designed to measure static air pressure,
which it relates to an indicated altitude.

As the aircraft ascends,
the static pressure in the instrument case decreases, which allows the
enclosed capsule to expand, and this in turn moves the needle on the
instrument face to indicate a corresponding altitude.

For a descent, the opposite function applies.

A sub-scale setting device is included so that the instrument can be
zeroed to various datum elevations.

(See Q: Give the definitions of the
following altimeter sub-scale settings, page 130.)

The altimeter capsule is calibrated to full international standard
atmosphere (lSA) mean sea level (MSL) conditions, i.e., + 15C,
29.92 in/1013 millibars, and 1225 g/m3.

Question 9

Q

Pressure Flight Instruments

Give the definitions of the following altimeter sub-scale settings?

QNH
QFE
QFF
QNE

Answer

A

QNH - is a local altimeter setting that makes the altimeter indicate the aircraft’s altitude above mean sea level (AMSL) and
therefore airfield elevation.

There are two types of QNH:
1. Airfield QNH
2. Regional QNH, which is the lowest forecast QNH in an altimeter
setting region.

QNH is QFE reduced to sea level using international standard atmosphere (ISA) values for the calculation.

QFE. This zeros the altimeter on the airfield elevation datum. There
are two types of QFE:
1. Airfield QFE is measured at the highest point on the airfield.
2. Touchdown QFE is measured at the touchdown point of the runway
in use for precision approaches.

QFF. This is similar to QNH except that it uses the actual conditions
(not ISA) to find the sea level pressure. It is used more commonly by
meteorologists than by pilots.

QNE. This is not an altimeter setting but is the height shown at
touchdown on the altimeter with 29.92 in or 1013 millibars (hPa) set
on the sub-scale. It is used at very high aerodromes where QFE pressure
is so low that it cannot be set on the altimeter sub-scale.
Standard setting. 29.92 in or 1013 hPa millibars standard setting
will give altimeter readings as a pressure altitude or flight level and
is used for traffic controlled airspace above the transition layer.

Question 10

Q

Pressure Flight Instruments

What are the aviation definitions of height, altitude, and flight level?

Answer

A

Altitude - is the measured distance above the local pressure setting (i.e.,
QNH) or altitude above mean sea level (MSL).

Flight level - is the measured pressure level above the 29.92-in/1013-
millibar datum.

Question 11

Q

Pressure Flight Instruments

What are the altimeter instruments errors?

Answer

A

The altimeter instrument errors are as follows:

Instrument error
Pressure error (also known as position or configuration error)
Time-lag error
Barometric error
Temperature/density error
Blocked static port

Question 12

Q

Pressure Flight Instruments

What are the altimeter indications and actions for a blocked static port?

Answer

A

A static line blockage means that the static pressure in the altimeter
instrument case remains a constant value.

Therefore, the altimeter will
display the altitude where the blockage occurred regardless of any actual change in the aircraft’s altitude.

The actions for a blocked static line causing an unreliable altimeter
reading would be

To ensure that the pitot static probe anti-ice heat is on (pitot heat),
if applicable.
To use an alternative, such as a static source or an air data computer,
if applicable.
‘Ib use a limited flight panel, i.e., standby altimeter or vertical speed
indicator (VSI), if available.
To fly correct attitude and power settings, especially for level flight.

Question 13

Q

Pressure Flight Instruments

Given a temperature deviation from ISA of -36°C, the pressure altimeter will

(a) over-read,
(b) under-read, or
(c) read correctly, and why?

Answer

A

The altimeter will over-read because the temperature deviation is
colder than the international standard atmosphere (ISA); i.e., the
altimeter reads an altitude higher than the actual altitude of the
aircraft.

(See Q: What density errors are commonly experienced?
page 119.)

Question 14

Q

Pressure Flight Instruments

What do you know about servo-assisted altimeters?

Answer

A

A servo-assisted altimeter increases the accuracy of a simple pressure
altimeter because its design no longer relies on a direct mechanical
link between its capsule and the altitude pointer on the instruments
display dial.

Instead, the servo-assisted altimeters use an electrically
conducted E&I bar arrangement.

Question 15

Q

Pressure Flight Instruments

How does a vertical speed indicator (VSI) instrument work?

Answer

A

The VSI instrument measures the rate of change of static pressure and
displays this as a rate of climb or descent (expressed as feet per minute, or fpm) on the VSI instrument face.

The capsule is fed with static pressure and reacts immediately to any change in static pressure,
whereas the static pressure feed into the case is restricted or slowed
by a metering unit, thus creating a differential static pressure between
the capsule and the case.

As long as the aircraft continues to climb
or descend, the VSl will translate this as a rate of climb or descent
measurement on the instrument dial face.

Question 16

Q

Pressure Flight Instruments

What errors do the vertical speed indicator (VSI) instrument suffer from?

Answer

A

The errors that the VSI instrument suffers from are

Instrument time-lag error
Pressure error (also known as position error)
Maneuver error

Question 17

Q

Pressure Flight Instruments

What do you know about an instantaneous vertical speed indicator (IVSI)?

Answer

A

The IVSI was designed to counter the time-lag error experienced by
simple VSI.

The IVSI uses two spring-loaded dash pots in the static
line before the capsule that cause an immediate differential pressure
to be sensed due to their inertia at the start of a climb or descent.

Once the aircraft is established in a climb or descent, the dash-pots are
centered by their springs, and when the aircraft starts to level out,
the opposite inertia of the dashpots produces an immediate change in the
reading on the IVSI display.

Question 18

Q

Pressure Flight Instruments

What are the advantages of an instantaneous vertical speed
indicator (IVSI)?

Answer

A

The advantage of an IVSI is the immediate display of any change in
the aircraft’s rate of climb or descent (ROC/ROD).

Question 19

Q

Pressure Flight Instruments

What are the disadvantages of an instantaneous vertical speed
indicator (IVSI)?

Answer

A

The disadvantage of an IVSI is that the dashpots, which sense the vertical
acceleration of the aircraft, are also affected by the acceleration
in a turn.

Therefore, the IVSI has an error that it initially shows as a
rate of climb (ROC) when applying large angles of bank, i.e., over 40
degrees of bank.

However, if the turn is maintained, the IVSI will stabilize
to zero but then indicates a rate of descent (ROD) as the aircraft
rolls out of the turn.

Question 20

Q

Pressure Flight Instruments

What are the vertical speed indicator (VSI) indications and actions for a
blocked static port?

Answer

A

A static line blockage means that the static pressure in the VSI instrument
capsule and case via the metering unit both remain a constant value.

Therefore, the VSI display will read zero at all times regardless
of any actual change in the aircraft’s rate of climb of descent
(ROC/ROD).

The actions for a blocked static line causing an unreliable VSI reading
would be
1. To ensure that the pitot static probe anti-icing heating (pitot heat)
is on, if applicable.

To use an alternative, such as a static source or an air data computer,
if applicable.
To use a limited flight panel, i.e., altimeter, if available.
To fly correct attitude and power settings.

Question 21

Q

Pressure Flight Instruments

How is air temperature measured?

Answer

A

Either a total head thermometer or a rose-mount probe that is
extended into the free airstream commonly measures air temperature.
Usually this temperature is displayed to the pilot on a total air
temperature (TAT) gauge.

(See Q: Describe total air temperature,
page 224.)

In flight, TAT is only a function of the ram effect ofthe air entering
the probe, and pitot heat is not considered when calculating outside air
temperature (OAT).

Question 22

Q

Pressure Flight Instruments

What do you know about air data computers?

Answer

A

Modern aircraft feed their static and pitot lines into an air data
computer (ADC) that calculates the RAS, TAS, MN, TAT, ROC, and
ROD and then passes the relevant information electronically to the
servo-driven flight instruments (not the standby instruments, which
retain their own direct static / pitot feeds).

The advantage of the ADC system is that the data calculated can be
feed to the following:
1. Autopilot (AP)
2. Flight director system (FDS)
3. Flight management system (FMS)
4. Ground proximity warning system (GPWS)
5. Navigation aids
6. Instrument comparison systems

Question 23

Q

Gyroscopic Flight Instruments

What are the gyro flight instruments?

Answer

A

The gyroscopic flight instruments are

Directional indicator (DI)
Artificial horizon (AH)
Turn and slip indicator or tum coordinator

Question 24

Q

Gyroscopic Flight Instruments

What is a gyroscope?

Answer

A

A gyroscope is a body (usually a rotor/wheel) rotating freely in one or
more directions that possesses the gyroscopic properties of rigidity and
precession

Question 25

Q

Gyroscopic Flight Instruments

How does a gyroscope work?

Answer

A

A gyroscope measures the force experienced on its rotor body during a
maneuver of an aircraft.

The rotor is usually suspended in a system of
frames called gimbals, which are arranged at right angles to each other
and are used as a conduit to transfer the force experienced on the rotor
to a displayed measurement on the instrument face.

Question 26

Q

Gyroscopic Flight Instruments

What is gyroscopic wander?

Answer

A

Any movement of the gyroscope’s spin axis away from its fixed direction
is called wander, and if this occurs, it gives rise to inaccurate
instrument readings.

The rigidity of a gyroscope system is responsible for maintaining the
direction of the spin axis and is fixed in space.

Question 27

Q

Gyroscopic Flight Instruments

What is the gyroscope caging system, and why is it used?

Answer

A

A caging system locks the gyroscope, i.e., artificial horizon, in a fixed
position, especially when the gyroscope is not being used, i.e., when
parked, and for some aircraft, it is recommended during aerobatic
maneuvers.

Caging a gyroscope in this manner will prevent it from
toppling (rigid in space), and thus when the aircraft is restarted, the
instrument reaches its fully erect position very quickly.

Question 28

Q

Gyroscopic Flight Instruments

What is real wander of a gyroscope?

Answer

A

Real wander occurs whenever the direction of a gyroscope’s spin axis
actually moves from its alignment in space. If this occurs, it gives
rise to inaccurate instrument readings.

Real wander can be either

(1) induced deliberately by applying an external correcting force,
e. g., as in the alignment oftied gyroscopes, or

(2) caused by imperfections
in the gyroscope, e.g., unbalanced gimbals or bearing friction.

Note: This is also known as mechanical drift.

Question 29

Q

Gyroscopic Flight Instruments

Describe the directional indicator (DI) instrument.

Answer

A

The DI is a gyroscope that displays the aircraft’s heading using a compass
rose display.

The DI consists of
1. A tied gyroscope.

The gyroscope rotates about the earth’s horizontal axis.
Two gimbals.
Three planes offreedom (i.e., the gyroscope’s spin axis and the pitch
and roll axes of the gimbals).
The gyrocope axis is aligned (direction) to true north.

Question 30

Q

Gyroscopic Flight Instruments

What is apparent wander of a gyroscope?

Answer

A

Apparent wander is a natural phenomenon.

A directional indicator
(DI) gyro appears to wander not because of any real changes in the
direction of the gyroscope’s spin axis alignment in space but because
its orientation has changed due to rotation of the earth.

If this occurs,
it gives rise to an incorrect heading display.

(See Q: What is gyroscopic
wander? page 135.)

Question 31

Q

Gyroscopic Flight Instruments

How do you correct for apparent wander?

Answer

A

Depending on the sophistication of the instrument, apparent wander
is corrected in one of two main ways:

By periodically (10- to 15-minute intervals) realigning the directional
indicator (DI) to the magnetic compass heading using the slaving
knob on the DI.
If the DI instrument is fitted with a latitude nut, it produces an opposite
error to the earth’s rotation (i.e., 15 X sin latitude in degrees per
hour) to give an adjusted heading.

If, however, the aircraft was moved
away from the latitude at which the lat nut was set, then an error,
either positive or negative, would arise because the degree of apparent
wander varies with latitude; i.e., it increases toward the poles.

Note: On early instruments, this was a real nut that was screwed in
or out to provide the necessary imbalance in drift on the gyroscope’s spin
axis for the aircraft’s actual latitude. On modern aircraft, this effect is
accomplished by onboard computer software adjustments.

Question 32

Q

Gyroscopic Flight Instruments

What is transport wander on an uncorrected gyroscope?

Answer

A

Transport wander is a form of apparent wander. If a directional indicator
(DI) gyroscope is aligned to true north at one place on the earth
and then the aircraft is moved to another east-west position on the
globe, the gyroscope axis will be out of alignment.

This is known as
transport wander on uncorrected gyroscopes.

Transport wander + apparent wander = total apparent wander

Flights north-south produce no transport wander but will produce
apparent wander as the latitude changes.

Question 33

Q

Gyroscopic Flight Instruments

What errors do a directional indicator (DI) suffer?

Answer

A

ADI suffers from…

(1) gyroscope system failures and
(2) total wander errors.

Question 34

Q

Gyroscopic Flight Instruments

What is the advantage of the directional indicator (DI) over the magnetic
compass?

Answer

A

The rigidity of the DI gyroscope gives steadier heading information than
the magnetic compass, which suffers from turning and acceleration errors.

Question 35

Q

Gyroscopic Flight Instruments

Describe the air-driven artificial horizon instrument.

Answer

A

The artificial horizon is the primary attitude instrument that measures
and displays the pitch and roll of the aircraft about the horizon level.

The artificial horizon consists of the following:

An earth gyroscope.
The gyroscope rotates about a vertical axis.
Two gimbals.
Three planes offreedom
a. The gyroscope’s spin axis.
b. Pitch and roll axis of the gimbals.
The gyroscope’s axis is aligned to the earth’s vertical.

Simply, the aircraft moves around the artificial horizon gyroscope, and
the gimbals measure the aircraft’s pitch and roll maneuvers.

Question 36

Q

Gyroscopic Flight Instruments

What errors do an artificial horizon experience?

Answer

A

The artificial horizon experiences the following errors:

Turning errors
Acceleration errors
Real wander of the gyroscope’s spin axis away from its alignment
with the earth’s vertical.
(See Q: What is real wander of a gyroscope?
page 136.)

Turning and acceleration errors in the artificial horizon gyroscope are
caused by lateral acceleration in turns and by the aircraft’s acceleration
and deceleration forces that induce a false position indication of the
gyroscope’s vertical axis.

Note: Remember, the artificial horizon is an earth gyroscope with
its spin axis in the earth vertical.

Question 37

Q

Gyroscopic Flight Instruments

What are the indications and actions for a failed artificial horizon?

Answer

A

The indications of a failed air-driven artificial horizon instrument

are. ..
1. Low reading on the suction gauge
2. Possible warning flag on some instruments

Action required is to re-erect the gyroscope.

This is accomplished in
flight by caging and uncaging the instrument when the aircraft is
straight and level and at a constant speed to achieve an approximate
re-erection.

However, if the suction reading is still low, the artificial
horizon ‘Will still be unstable, and therefore, secondary flight instruments,
e.g., turn coordinator, vertical speed indicator (VS!) , etc.,
should be monitored.

Question 38

Q

Gyroscopic Flight Instruments

Describe the electrically driven artificial horizon instrument.

Answer

A

Electrically driven artificial horizons use the same basic principles as the air-driven instruments, with a gyroscope tied to the earth’s vertical
and two gimbals.

(See Q: Describe the air-driven artificial horizon instrument, page 137.)

There are some fundamental differences, however, as follows:

Most gyroscopes/rotors of electrically driven artificial horizons
rotate clockwise when viewed from above.
Electrically driven artificial horizons use an electric squirrel-cage
motor to drive the rotor at approximately 22,000 rpm, which is
about twice the speed of an air-driven instrument.

Therefore, the
electric artificial horizon is more rigid.

Electric erection systems are very fast, and because of this, there is
no need for the gyroscope to be pendulous, although some do
remain to some extent pendulous.

Electric erection system also can
be cut out at will.

Acceleration and turn errors are minimized or completely eliminated
because the instrument has little or no pendulous and its normal
erection system can be cut out at certain values of longitudinal or lateral (balanced turn) acceleration.
The electrically driven artificial horizon has a freedom of pitch of
+/-85 degrees and unlimited roll.

Question 39

Q

Gyroscopic Flight Instruments

What is a servo-driven attitude directional indicator (ADI) (or remote
artificial horizon)?

Answer

A

A servo-driven, attitude directional indicator, also called a remote
artificial horizon, is used on modern aircraft to display attitude information
(pitch and roll) that has been calculated by the aircraft’s inertia
navigation/reference system (INS/IRS) platforms.

(See Q: What is an
INS / IRS? page 92.)

Question 40

Q

Gyroscopic Flight Instruments

Describe the turn and slip (turn coordinator) indicator instrument.

Answer

A

The turn and slip indicator is in effect two instruments combined as a single unit.

One measures turn, and the other measures slip or skid.

Turn is the movement about the aircraft’s yaw axis (the aircraft’s vertical) that results in a change of direction.

Slip is a lateral force into the turn.
Skid is a lateral force out of a turn.

The turn and slip instrument consists of the following:
1. A rate gyroscope.

The gyroscope rotates about a horizontal axis.
One gimbal, which is pivoted about the aircraft’s fore and aft axis that measures the aircraft’s yaw when the precessed force in this plane of freedom is sensed.
Two planes of freedom:
a. The gyroscope’s spin axis.
b. Yaw axis of the gimbals.
The gyroscope’s axis is aligned to the aircraft’s lateral axis.

Question 41

Q

Gyroscopic Flight Instruments

What errors does the turn and slip indicator experience?

Answer

A

The turn indicator gyroscope suffers from
1. Gyroscope system failures

Looping error.
(This is an inherent design error in the instrument,
and as a result, with any yaw condition the gyroscope will tilt.)
Real wander of the gyroscope’s spin axis.
(See Q: What is real wander of a gyroscope? page 136.)

Question 42

Q

Gyroscopic Flight Instruments

What is the turn coordinator?

Answer

A

The turn coordinator is an advanced development of the earlier turn indicator.

It is similar to the turn indicator instrument, except that its single gimbal is raised at the front by 30 degrees so that the instrument is sensitive to both roll and yaw, and it begins to indicate a turn as soon as the roll-in begins.

However, the turn coordinator only indicates rate 1 turns accurately and should not be confused with an artificial horizon because it displays no attitude information. A warning,

“No Attitude Information,” is often written on the instrument face.

Question 43

Q

Magnetism and Compass Instruments

Describe the earth’s magnetic field

Answer

A

The earth has a magnetic iron core, which makes the earth act like a giant magnet with north and south magnetic poles.

The magnetic poles are slightly offset from the geographic poles, and the earth’s surface is covered with a resulting weak magnetic field that radiates
from its magnetic poles.

Because the true and magnetic poles are not coincident, the true and magnetic meridians that radiate from their respective poles are also not coincident.

The angular difference between a corresponding true
and magnetic meridian is called variation.

If the magnet points slightly to the east of true north, then the variation is said to be east (plus), and if the compass points to the west of true north, then the variation is said to west (minus).

That is, Magnetic heading + easterly variation = true heading…
Variation east magnetic least.
Variation west magnetic best.
(See Q: What is magnetic variation? page 89.

Question 44

Q

Magnetism and Compass Instruments

Describe the magnetic compass instrument (direct reading compass).

Answer

A

The direct reading compass is the primary source of directional information
in all types of aircraft and displays compass heading. (See Q: What is compass direction? page 89.)

It is comprised of a freely suspended horizontal magnet attached to a compass card that is enclosed in a liquid-filled case.

The magnet will swing so that its axis points roughly north-south, and the aircraft moves around the magnet so that the compass heading of the aircraft is read off the compass card against a lubber line on the instrument case.

Question 45

Q

Magnetism and Compass Instruments

What is magnetic dip?

Answer

A

Magnetic dip is the natural phenomenon of the vertical component of
the magnetic field over the earth’s surface and its effect on the magnetic
compass.

The earth’s magnetic field has two components or forces: a horizontal
force parallel to the earth’s surface that is used to align the compass
with magnetic north and therefore to determine direction and a vertical
force that causes the needle to dip down.

At the magnetic equator, the horizontal force is dominant, and
therefore, there is no dip and the compass is accurate.

However, as you move closer to either of the magnetic poles, the vertical component increases, and this induces the magnetic bar in the compass to dip
down to align itself vertically with the magnetic field.

Question 46

Q

Magnetism and Compass Instruments

Explain compass swinging.

Answer

A

Compass swinging is a procedure to check the accuracy of and to adjust
an aircraft’s magnetic compass.

A compass should be swung when any of the following occurs:
1. The compass is new.

Any equipment influenced by electrical or magnetic energy in the
vicinity of the compass has been altered.
Having passed through a severe magnetic storm.
After a considerable change in latitude.
After any inspection of either
a. The compass.
b. Nearby equipment influenced by electrical or magnetic energy.
Whenever there is doubt about the accuracy of the compass.

Question 47

Q

Magnetism and Compass Instruments

Describe the errors of the magnetic compass.

Answer

A

The errors of the magnetic compass are

 1. Acceleration/deceleration errors.
2. Turning errors.

Question 48

Q

Magnetism and Compass Instruments

Describe the remote indicating compass.

Answer

A

The remote indicating compass is a combination of the directional indicator (DI) and the magnetic compass instruments as a single instrument.

It uses the rigidity of the gyroscope to avoid compass turning and acceleration errors and a magnetic north-sensing input to prevent DI gyroscope wander to maintain its correct orientation at all times without any external influence.

(See Qs: Describe the directional indicator and describe the magnetic compass, pages 136 and 142.)

The remote indicating compass is made up of the following:

Detector unit
G;YToscope
Feedback system

Question 49

Q

Radio Instruments

Describe the relative bearing indicator (RBI) instrument and how it works.

Answer

A

The RBI is a simple automatic direction finder (AD.B’) instrument that is used to display non directional beacon (NDB) navigation information.

The RBI is comprised of the following:
1. A fixed 360-degree compass card. The 000-degree position is at the
12 o’clock position and thus the aircraft heading.

An ADF needle that seeks out and shows the relative bearing of the NDB from the aircraft’s heading.

The pilot, in conjunction with the directional indicator (DI), uses the RBI by adding the relative bearing (ADF needle) to the aircraft’s magnetic heading (DI) to determine the QDM to the NDB.

A further development of the RBI instrument is the moving-card ADF, which can be orientated manually to the aircraft’s heading.

This subtle change means that the needle head now indicates the QDM to the NDB.

Question 50

Q

Radio Instruments

Describe the radio magnetic indicator (RMI) instrument and how it works.

Answer

A

The RMI can be used to display automatic direction finder (AD F) or VHF omni range (VOR) navigation information and is regarded as an advanced development of the RBI.

The RMI is comprised of the following:

A remote indicating 360-degree compass card that is continuously and automatically aligned with magnetic north.
Therefore, the RMI displays the aircraft’s magnetic heading at the top of the dial.
Either a single or dual needle that seeks out the direction of the station to which the pilot is tuned and is superimposed onto a compass card that is orientated to the aircraft’s magnetic heading.

This means that the needle’s head indicates a QDM and the needle’s
tail indicates a QDR.

Selection button, sometimes known as rabbit ears, enables the pilot to change between ADF and VOR needle indications.

ADF selection. Selected as an AD.B’ needle, it seeks out the direction of a nondirectional beacon (NDB) station as a QDM.

The relative bearing of the beacon from the aircraft is the sum of the QDM minus the aircraft heading.

VOR selection. Selected as a VOR needle, the head indicates the QDM and the tail indicates the QDR, which itself is an indication of the VOR radial the aircraft is on.

Question 51

Q

Radio Instruments

Describe the omni bearing indicator (OBI) instrument.

Answer

A

The OBI indicator is a navigation instrument sometimes referred to as a first-generation VHF omni range (VOR) indicator.

It is used by the pilot to select the required VOR radial and to display tracking guidance relative to the selected radial.

If the aircraft is on the selected radial, the VOR needle or course deviation indicator (CDI) will be centered,
and if the aircraft is not on the selected courseltrack, then the CDr will not be centered.

The OBI is a track-up display; i.e., the selected track accommodates the top of the dial position regardless of the aircraft’s heading.

Note: Later versions of the OBI instrument also have the capability of displaying instrument landing system (ILS) information.

Note: Course is another term for track.

Question 52

Q

Radio Instruments

Describe the purpose-built instrument landing system (ILS) indicator.

Answer

A

A purpose-built ILS display instrument is a further development of the omni bearing indicator (OBI) instrument.

It still acts as a VHF omni range (VOR) navigation display when a VOR frequency is selected, but
it also can act as an ILS display instrument when an ILS frequency is selected to guide a landing aircraft along both a localizer track and a glide slope descent path.

The ILS indicator is a track-up display, like the OBI instrument.

That is, the selected track (localizer) accommodates the position at the top of the dial regardless of the aircraft’s heading.

Question 53

Q

Radio Instruments

Describe the horizontal situation indicator (HSI) instrument.

Answer

A

The RSI is a sophisticated primary navigation instrument.

It is comprised of a remote indicating compass that displays the aircraft’s directional magnetic heading and an instrument landing system/VHF omni range (ILS/VOR) display that gives an easy-to- understand display of the aircraft’s situation in relation to the selected VOR radial or ILS localizer and glide slope and the aircraft’s magnetic heading.

The HSI instrument is found in most modern aircraft and consists
of the following:
1. Remote indicating compass
2. Combined course/track and deviation bar
3. Localizer dot scale
4. Glide slope dot scale

Question 54

Q

Radio Instruments

Describe a radio altimeter and how it works.

Answer

A

Radio altimeters provide an accurate height measurement from 2500 ft down to 50 ft above ground level (AGL) for pulse radar beams or 0 ft
for continuous-wave radar beams.

They are usually fitted alongside barometric altimeters in most commercial aircraft.

The basic principle ofthe radio altimeter is that a wide conical beam is directed vertically down toward the ground, and the time taken for the reflected signal to return corresponds to its height.

Question 55

Q

Radio Instruments

At what height does a radio altimeter normally become active?

Answer

A

A radio altimeter normally becomes active at 2500 ft above the ground for both separate dial and electronic flight instrument system (EFIS) radio altimeter instruments.

Note: Some types of radio altimeters may become active at a different
height.

Question 56

Q

Advanced Flight Instruments

What does EFIS stand for?

Answer

A

Electronic flight instrument system

Question 57

Q

Advanced Flight Instruments

What is an electronic flight instrument system (EFIS)?

Answer

A

EFIS is a fully integrated computer-based digital navigation system that uses color cathode-ray tube (CRT) types of electronic attitude directional indicator (EADI) and horizontal situation indicator (EHSI).

Question 58

Q

Advanced Flight Instruments

What components make up a typical EFIS?

Answer

A

An electronic flight instrument system has the following five main components:

Cathode-ray tubes (CRTs)
EFIS control panel
Symbol generators
EADI (electronic attitude directional indicator)
EHSI (Electronic horizontal situation indicator)

Question 59

Q

Advanced Flight Instruments

What is the advantage of an EFIS flight deck?

Answer

A

The electronic flight instrument system (EFIS) display has two distinct advantages over older, mechanically driven instruments.

First, it displays the same information in a clearer and more versatile manner.

Second, it can bring together additional data from several different
sources to present the pilot with the best possible attitude and navigation
information for a particular stage of flight on a dual or single display panel.

Question 60

Q

Advanced Flight Instruments

What is typically displayed on the EADI?

Answer

A

The electronic attitude directional indicator (EADI) display includes
the following:

Basic attitude information (pitch and roll) and a turn and slip
indicator (yaw) received from an inertia reference system (IRS)
Additional attitude information
a. Flight director command bars
b. Pitch limit symbols, also known as eyebrows
c. Rising runway
Speed indicator:
a. Speed tape (side of EADI)
b. Fast/slow speed indicator (speed trend)
c. Mach number and ground speed digital display
Navigation information:
a. L Nav or localizer deviation indicator (bottom of EADI)
b. V Nav or glide slope deviation indicator (right-hand side ofEADI)
Altitude, radio altimeter height, and decision height display
Autopilot, armed and engaged modes:
a. Autothrust
b. Pitch mode
c. Roll mode
d. Autopilot status

Question 61

Q

Advanced Flight Instruments

At what height would you expect the rising runway symbol on an electronic attitude directional indicator (EADI) to become active?

Answer

A

The rising runway normally becomes active at 200 ft radio altimeter, but this can vary because it is a type-specific design feature.

Question 62

Q

Advanced Flight Instruments

How is 0 ft represented by the rising runway on the electronic attitude
directional indicator (EADI)?

Answer

A

Zero feet is represented by the rising runway symbol reaching the base
of the aircraft symbol.

Question 63

Q

Advanced Flight Instruments

What are the electronic horizontal situation indicator (EHSI) instrument
modes?

Answer

A

The ERSI typically has seven display modes, which are as follows:

Full VORlILS
Full NAV
Expanded (arc) VORlILS
Expanded (arc) NAV
Map mode
CTR map mode
Plan

Question 64

Q

Advanced Flight Instruments

Which electronic horizontal situation indicator (EHSI) modes can display
the weather radar?

Answer

A

Weather radar typically can be overlaid on the following modes:

Expanded VORlILS
Expanded NAV
Map mode
Center map mode

Answer 65

A

There is no standard color coding used by all the different EFIS manufacturers.

However, in general, the following color scheme is the
most cmn]non:
Green - Active or selected mode, changing conditions

White - Present situation and scales

Magenta - Command information and weather radar turbulence

Cyan - Nonactive background information

Red - Warning

Yellow - Caution

Black - Off

Answer 66

A

Head-up display.

This normally consists of electronic attitude directional
indicator (EADI) information, i.e., speed, attitude, and flight
director bars, etc

Answer 67

A

VHF radio transmissions are used for short-range communications.

VHF radio uses line-of-sight propagation paths and allows reception and transmission at any point within its area of coverage, namely, from the ground station to its maximum range.

Civil agencies uses ultrahigh frequency (UHF) in the 118- to 137-MHz band at 12.5-kHz intervals.

This range usually gives good reception and only slight interference from static tied to atmospheric attenuation.

Answer 68

A

The following factors affect the range of a VHF communication:
1. Transmitter power

Frequency
Height of transmitter and receiver
Obstructions
Fading

Answer 69

A

HF radio transmissions are used for long-distance communications between two specific points only, unlike VHF.

It uses predictable sky wave propagation paths that are refracted off the earth’s ionosphere over great distances.

Answer 70

A

At night,the HF range (skip distance) is approximately twice of the daytime .

This is so because of variation in the ionosphere.

During the day, especially in the summer, the sun generates ion particles that make up the ionosphere’s D layer at a height of approximately 75 km.

This layer is of sufficient density to refract HF sky waves.

However, at night or during winter days when the exposure to the sun is less, the D layer disappears, and therefore, the HF sky waves are refracted by
the ionosphere’s E layer at a height of approximately 125 km.

This increases the range (skip distance) of an HF transmission because of
the greater vertical distance to the higher E layer before it is refracted.

Therefore, because of the higher ionosphere at night, you need a lower frequency to reach the same receiver distance; typically, half the daytime frequency is needed because the signal is refracted more.

Answer 71

A

The following factors affect the range of an HF communication:

Transmitter power
Frequency
Time of day
Season
Location
Disturbance of the ionosphere

Answer 72

A

Traffic (Alert) Collision Avoidance System (TCAS) provides traffic information and maneuver advice between aircraft if their flight paths are conflicting with each other.

TCAS uses the aircraft’s secondary surveillance radar (SSR) transponders and is completely independent of any ground-based radar units.
TCAS is rapidly becoming a mandatory requirement
around the world and is already established in U.S. airspace.

TCAS I is an early system that provides traffic information only.

TCAS II is a later system that provides additional maneuver advice, but in the main is restricted to vertical separation.

TCAS IV is a new system under development (1998) that will give resolution advisories (RAs) in the horizontal and vertical planes.

However, further development of TCAS IV is likely to be canceled in preference to ADS-B.

Answer 73

A

An aircraft’s traffic collision avoidance system (TCAS) will interrogate the secondary surveillance radar (SSR) transponders of nearby aircraft to plot their positions and relative velocities.

Direction-finding aerials obtain the relative bearings of other aircraft, and distance is calculated by using the time delay between the transmitted and received signals.

With this information, the TCAS computer can determine the track and closing speeds of other aircraft fitted with transponders, and where it determines a collision is possible, it provides visual and aural warnings as well as command actions on how to avoid
the collision.

This is all done with vertical avoidance commands only.

As yet, no turn commands are given.

The warnings and advice (advised actions) from the system have different levels:

Initially. A traffic advisory (TA) warning is generated for other traffic that may become a threat. No maneuver is advised or should be taken.

Collision threat. A resolution advisory (RA) warning is generated when an aircraft is considered to be on a collision course.

Advice on a maneuver in the pitching plane, i.e., rate of climb or descent, to avoid the collision is generated that can be increased or decreased as the threat increases or reduces until a clear of conflict notice is given.

Therefore, you only respond to an RA, which should be done promptly and smoothly and should take precedence over air traffic control (ATC) clearance to avoid immediate danger.

RA use should be restricted in the following circumstances:

In dense traffic area (limited to TA use)
Descent recommendations inhibited below 1000 ft
All RAs inhibited below 500 ft (Note: All TAs also restricted below 400 ft) TCAS can cope with mode A, C, and S transponders.

However, when both aircraft are equipped with TCAS II and mode S, the advice on how to avoid a collision will be coordinated by the mode S data link between the two aircraft.

Answer 74

A

ACAS is a European airborne collision avoidance system (ACAS II).

Answer 75

A

Automated Dependent Surveillance-Broadcast (ADS-B) system is a
traffic collision avoidance system similar to TCAS.

ADS-B incorporates cockpit display of traffic information and is overall a more capable system than TCAS II.

Answer 76

A

Ground proximity warning system.

The GPWS is essentially a central computer system that receives various data inputs on configuration, height/altitude, and instrument landing system (ILS) glide slope deviation.
(See Q: What are the inputs to a GPWS? page 154.)

It then calculates these inputs to detect if any of the following dangerous and/or potentially dangerous circumstances exist:

Excessive barometric rate of descent
Excessive terrain closure rate
Height loss after takeoff
Flaps or gear not selected for landing
Too low on the ILS glide slope
Descending below approach minima

These circumstances form the six main working modes of the GPWS.

If the central computer determines that a boundary of any of the various modes has been exceeded, it will activate aural and visual alerts to warn the flight crew using the following cockpit equipment:
1. Speakers.

A pair of red warning lights with “Pull Up.”
A glide slope deviation inhibited amber advisory light

Answer 77

A

Enhanced ground proximity warning system.

It can be shown on navigation displays by using the weather system.
Probable wind-shear aural and visual warnings also can be generated to warn of an impending possibility of encountering wind-shear ahead.

Answer 78

A

The inputs to a ground proximity warning system (GPWS) are as follows:

Barometric altitude for rate of descent (ROD) calculations
Radio altimeter
Flap position
Gear position
Instrument landing system (lLS) glide slope
Approach minima
Throttle position

Answer 79

A

There are six main ground proximity warning system (GPWS) modes, of which some have further subdivisions:

Mode 1. Excessive barometric rate of descent
Mode 2. Terrain closure
Mode 3. Sinking flight path after takeoff or go-around
Mode 4. Gear and flap not selected
Mode 5. Instrument landing system (ILS) glide slope deviation
Mode 6. Approach minimas
Mode 7. Windshear warning

Answer 80

A

Highest priority
Whoop, whoop, pull up (Modes 1, 2, 3, 4)

Terrain, terrain (Mode 2)

Too low gear (Mode 4a)

Too low flap (Mode 4b)

Minima, minima (Mode 6)

Sink rate, sink rate (Mode 1)

Don’t sink, don’t sink (Mode 3)

Lowest priority:
Glide slope, glide slope (Mode 5)

Answer 81

A

For a ground proximity warning system (GPWS) alert, the initial action required is a corrective response; i.e., “Too low flaps” requires the corrective action of lowering the flaps accordingly.

For a GPWS warning, the immediate action required is a full wind-shear go-around, i.e., maximum go-around thrust and climb attitude.

Answer 82

A

Modern aircraft are provided with windshear warnings by using air data computer-detected changes in airspeed to calculate the presence of a windshear phenomenon, which it feeds to the ground proximity
warning system (GPWS), which generates a "Windshear, windshear" aural and visual display on the main attitude directional indicator
(ADI) flight instrument.

Windshear warning systems are active from
the ground level to a height of 1500 ft.

A windshear warning requires an immediate go-around at full thrust and maximum flight director pitch-up attitude to avoid ground contact.

If, however, the aircraft still does not climb, then the aircraft should be pitched up to its maximum pitch limit symbols or eyebrows.
(See Q: What is windshear? page 254.)

Answer 83

A

First: Windshear

Second: Ground proximity warning system (GPWS)

Third: Traffic collision avoidance system (TCAS)

Answer 84

A

What is the purpose of a flight management system (FMS)?

The purpose of an FMS is to manage the aircraft’s performance and route navigation to achieve the optimal result.

(See Q: Describe a typical flight management system, page 157.)

These managed data then can be used for either
(1) advisory crew information only or
(2) to direct the auto-throttle and autopilot to steer
the aircraft.
(See Q: Describe an autopilot system? page 158.)

Answer 85

A

The three sources of flight management system data are

Stored databases
Pilot inputs via the control display unit (CDU)
Other aircraft systems, which are fed automatically into the FMS.

These input sources are fed into the flight management computer
WMC) and are duplicated for both performance and navigation management
functions.

Answer 86

A

The flight management system WMS) combines data from various aircraft systems, which are fed into a central computer (FMC) to manage the route navigation and the aircraft’s performance.

There are two main operational functions of the FMC/CDU:

 1. Route navigation management
2. Aircraft performance management

Answer 87

A

The L NAV and V NAV functions are predetermined or custom-made route profiles.

They are based on the FMC’s managed performance
and navigation data and are stored in the FMC databases so that they can be selected via the control display unit (CDU) to be flown either as an autopilot and auto-throttle modes of operation or as a guide for
manual flying.

The LNAV (lateral navigation) function guides the aircraft’s lateral movement and is available from takeoff to localizer capture, and the

VNAV (vertical navigation) function guides the vertical path of the aircraft, including climb and descent profiles.

A stored company route will contain a complete lateral and vertical flight profile, which can be amended by the crew if required.

Answer 88

A

An autopilot system is an integrated flight control system that enables an aircraft to fly a prescribed route and to land at a designated airport without the aid of a human pilot.

Answer 89

A

The purpose of an autopilot system is to relieve the pilot of the physical and mental fatigue of flying the aircraft, especially during long flights.

This will result in the pilot being more alert during the critical phase of landing the aircraft, thus improving safety.

Answer 90

A

When engaged, the autopilot is responsible for the following:

Stabilizing the aircraft
Maneuvering the aircraft

Answer 91

A

The response of an autopilot is substantially faster than that of a human pilot.

A human pilot takes approximately 0.5 second in detecting a change in the aircraft’s attitude and then a further delay in deciding which control to apply to oppose the disturbance.

An autopilot, however, will detect a disturbance and put on the required control to correct the disturbance
in approximately 50 ms.

Answer 92

A

This is really a type-specific question, and the reader should refer to his or her own aircraft type; however, the following answer, which is based on the B737 -300 autopilot system, is given as a example.

The autopilot modes of operation are normally the following:
1. Heading
2. Lateral navigation (L NAV)
Note: This is known as managed navigation for Airbus aircraft.
3. VOR / LOC (VOR / Iocalizer mode)
4. Altitude hold
5. Vertical speed
6. Level change
Note: This is known as open climb or descent for Airbus aircraft.
7. Vertical navigation VNAV)
Note: This is known as managed vertical navigation for Airbus aircraft.
8. ILS/approach

Answer 93

A

The flight director system (FDS) provides guidance information on the required aircraft maneuver in pitch and roll to gain, regain, or maintain the programmed flight path.

The flight director display is found on the primary flight instrument (ADI) as either a chevron indicator or a pair of vertical and horizontal bars.

The FDS uses the autopilot CAP) sensors and the aircraft’s flight
management computer (FMC) performance database to compute the
aircraft’s pitch and roll response to gain, regain, or maintain the
programmed flight path, and the flight control computer (FCC) positions
the FDS bars/chevron accordingly on the respective attitude
directional indicators (ADIs).

Answer 94

A

The errors of an FDS are primarily operating errors.

First, an error commonly occurs with interpretation of the FDS indication by the pilot, in that a pilot interprets the flight director bars as the flight path
(e.g., center and crossed flight bars as meaning that the aircraft is on track).

Second, the FDS is part of the autopilot system, and because of this, the flight director bars are geared to the autopilot’s quick response/reaction rate, which is far quicker than the ability of a human pilot.
on either side of the centerline.

Answer 95

A

An auto-land system is a function of the autopilot flight director system (FDS) and auto-throttle system that is engaged using the approach mode of operation.

It is designed to carry out automatic landings under
all visibility conditions by providing better guidance and control than that provided by a pilot from the interception of the localizer until the touchdown.

The auto-land system controls the aircraft about all three axes simultaneously.

This includes the use of yaw to control drift and use of the autopilot’s flight control computers, including sensors and instrument landing system (ILS) radio couplings, to accurately track the localizer
and glide path approach down to minim as that can include a full Cat III autoland.
(See Q: Describe an autopilot system, page 158.)

The auto-throttle is also used by the autoland and system to control and maintain the correct airspeed through engine power changes during
the approach, to retard thrust during the flare, and finally to automatically
disconnect at touchdown (type-specific).

Answer 96

A

Multiplex is a term used for an autopilot landing system that is comprised of two or more independent autopilots/channels that are used collectively to provide a redundant system design.

A multiplex autoland system can use either

A dual digital control computer channel known as a duplex system
A triple digital control computer channel known as a triplex system
A quadruple digital control computer channel known as a quadruplex system

The independent auto pilot/channel systems are interconnected, and together they provide continuous autoland control.

In the event of asingle autopilot/channel failure or a different reading, that system is
outvoted by the others and is disengaged automatically.

Answer 97

A

A fail passive automatic pilot landing system, also known as a land 2 system, is one that employs two digital control computer channels (duplex system).

In the event of a single control channel failure, there
is no significant out-of-trim condition or deviation of the flight path or
attitude.

However, the landing is not completed automatically due to a minimum dual channel system being required for a fully automated landing, thus requiring the pilot to assume control of the aircraft to complete the landing.

Answer 98

A

A fail operational automatic pilot landing system, also known as a
land 3 system, is one that employs three digital control computer
channels (triplex system).

These provide redundant operational capability,
whereby in the event of a single control channel failure below
the alert height, the approach, flare, and landing can be completed by
the remaining automatic systems due to the minimum required dual
channel system still being available.

This allows the automatic landing
system to work in a fail operational manner.

Answer 99

A

Autothrottle (AT) systems are designed to control and maintain thrust and/or airspeed, especially during an automatic approach and landing, by changing engine thrust.

They also may provide a constant closure rate
of the throttle levers during the autoflare phase on some designs.

The auto-throttle is part of the autopilot (AP) flight director system (FDS) and is available with or without the AP or FDS being engaged as long as a thrust or speed operating mode has been engaged.

An AT computer receives inputs from various sources, especially

(1) - The flight management computer (FMC), which calculates EPRlN] limits and targets and

(2) - APFDS pitch and speed targets and limits, which it
uses to calculate the engaged operating mode’s engine thrust targets and associated throttle lever positions (which are moved and held by servo
driven motors and a clutch system) to attain the desired engine thrust level.

(See Q: Describe the auto-throttle operating control modes, page 164.)

Answer 100

A

The autothrottle is engaged by a master switch on the mode control panel (MCP) being selected to “arm” and then an operating mode being selected either automatically by the autopilot or manually through
switches on the MCP.

Answer 101

A

The following can disconnect the auto-throttle (A/T):

The pilot can override the AT by applying normal pressure to the throttle levers.

This applies an opposing force to the servo drive,
which will automatically disengage the clutch.

The AT disengage switch located on the end of each throttle lever
can be pressed.
The AT engagement switch located on the mode control panel
(MCP) can be set to off.
The AT automatically disengages after touchdown and for various
type-specific abnormal situations.

Answer 102

A

The takeoff go-around (TOGA) switches (or gate on an Airbus aircraft)
provide a means of engaging the autothrottle and the flight
director in the takeoff or go-around mode. The TOGA switches are
located on the aft edge of each throttle lever.

Answer 103

A

The nonnal auto throttle’s modes of operation are

Takeoff thrust
Go-around thrust
Maximum continuous thrust
Airspeed
Airspeed/Mach hold

Answer 104

A

The advantages of a hydraulic system over a pneumatic system are as
follows: Hydraulic fluid is incompressible, and this makes the system
respond instantly and more efficient.

In addition, hydraulic fluid that
leaks from the system is easier to detect visually than air from a
pneumatic system.

Answer 105

A

The advantages of a pneumatic system over a hydraulic system are
as follows:

Air weighs less than hydraulic fluid, which is beneficial to the aircraft’s
overall weight limitations.
You do not have any problems of availability and cost with air,
which you could have with hydraulic fluids.

Answer 106

A

Most aircraft use the tricycle layout, where the two main undercarriage units are positioned just aft of the center of gravity and support up to 90 percent of the aircraft’s weight and the entire initial landing
shocks.

The nose-wheel unit keeps the aircraft level and in most cases
provides a means of steering.

Answer 107

A

The main purpose of retractable landing gear is to improve aircraft
performance by reducing the drag created by extended gear in flight.

Answer 108

A

The gear is operated by the crew member via a gear lever in the cockpit, and a system of green and red lights for each wheel indicate whether the associated wheel is down and locked (green) or up and
locked (red).

Gear retraction normally is accomplished by a hydraulic system, although pneumatic or electrical systems also can be used.

Answer 109

A

Nose wheel shimmy is unstable swiveling oscillation of the nose wheel due to the flexibility of tire sidewalls, especially at high speed.

Excessive shimmy can vibrate dangerously throughout the entire aircraft, causing wear in the wheel bearings, low tire pressures, and wear on the undercarriage linkage and mountings.

Answer 110

A

The nose wheel requirements are as follows:
1. To carry the aircraft’s direct compression load weight

To provide a towing attachment
To withstand shear loads
Castoring (The nose wheel must be able to castor freely when
subjected to compression and shear loading; i.e., right brake to
turn right.)
Self-centering (Whenever the weight is remove from the wheel, it
must be centered to ensure correct positioning of the wheel before
retraction. )
Steering
Antishimmy

Answer 111

A

Creep is the tendency of the tire to rotate slowly (creep) around the wheel hub as a result of a millisecond landing friction on the tire before
wheel spin occurs (usually because of a low tire pressure).

This creep, if excessive over a period of time, will cause the tire to tear out the inflation valve and cause the tire to burst on touchdown.

Answer 112

A

When the tire is installed a mark, usually a red dot, is placed on the tire sidewall, and a second dot is placed adjacent on the wheel hub.

From then on, any displacement of the red dots from each other indicates tire creep, and this can be seen easily during a pre-flight inspection.

Answer 113

A

Fusible plugs offer protection from tire blowouts caused by thermal expansion that is generated in the tire under extra hard braking conditions.

These fusible plugs are fitted in tubeless wheel hubs by means of a fusible alloy that melts under excessive heat conditions and allows the plug to be blown out by the tire air pressure. This prevents excessive pressure buildup in the tire by allowing the air to leak away slowly.

Answer 114

A

A chimed tire has a special sidewall construction that takes the form of a ridge built onto the sidewall that diverts runway water to the side, reducing the amount of water thrown up into the intake of rear-mounted engines.

Answer 115

A

Most aircraft braking systems use hydraulic fluid pressure to move friction brake pads (that are connected to small hydraulic pistons) against rotating brake plates to slow down the plates and therefore the wheel.

The brake system is engaged either by the manual application of the brake pedals or by the automatic braking system that controls a brake metering valve for each wheel that adjusts the amount of piston
movement and thereby the amount of pressure applied against each rotating wheel plate.

Answer 116

A

An automatic brake system regulates the amount of brake pressure by controlling the metering valve in the hydraulic brake line so as to maintain a constant deceleration rate until the aircraft reaches a complete
stop. Brake application is regulated with the reverse thrust applied to maintain the selected deceleration rate.

Answer 117

A

Prior to the takeoff run, the following factors affect tire temperature:
1. Outside air temperature (OAT) (reflects the tire ambient temperature)

Aircraft weight
Taxi time
Amount of braking (which generates heat in the brakes that is
transferred to the tires)
During the takeoff run, tire temperature depends on takeoff run (TOR)
time (i.e., determined by head/tailwind component, runway slope, and
pressure altitude).

All generate a temperature rise in the tires.Prior to the takeoff run, the following factors affect tire temperature rise in the tires.

Answer 118

A

Prior to the takeoff run, the following factor affects the brake temperature:

Taxi time (distance) and the number of brake applications used

During the takeoff run, the following factors affect the brake temperature:
1. Aircraft takeoff weight
2. Pressure altitude
3. Outside air temperature (OAT)
4. Runway slope
5. Tail/headwind
All generate a temperature rise in the brakes.

Answer 119

A

It is important to monitor tire temperature because an increase can lead to an increase in tire pressure, which causes the tire to expand, possibly too its blowout limit.

Answer 120

A

It is important to monitor the brake temperature, especially prior to commencing the takeoff run.

This is done to ensure that the aircraft’s
inertia, which has to be dissipated through the wheel brakes, will not cause the brakes to overheat and lose efficiency, bind, and even cause tire failure or fire if the takeoff were abandoned at VI.

Therefore, brake temperature must be below a certain limit prior to commencement of the takeoff run to ensure that the maximum brake energy limit is not
exceeded during an aborted takeoff run.

Answer 121

A

The downwind (with a crosswind) wheel brakes.

Answer 122

A

Reverse thrust.

Heavy jet aircraft have a high kinetic energy (momentum) during a landing roll or an aborted takeoff, and the most efficient method of stopping that maintains the initial deceleration rate when the aircraft
is at a high speed is best achieved by reverse thrust for two reasons:

The net amount of reverse thrust increases with speed because the
acceleration imposed on the constant mass flow is greater.

This is so because the aircraft’s forward speed is additional when using
reverse thrust as opposed to subtracting when in forward thrust.

The power produced is greater at high speeds because of the increased rate of work done. This means that the kinetic energy of the aircraft is being destroyed at a greater rate at higher speeds.

Answer 123

A

The purpose of an anti-skid system is to sense when the wheels are locked, i.e., not spinning, and to release brake pressure through the brake-modulating/metering valve system to generate wheel spin.

Wheel spin is required to maintain directional control and braking efficiency, which are necessary to ensure landing performance and are especially important in the operation of modern aircraft with high speeds, low drag, and high weights, particularly when coupled with
operation from short runways in bad weather.

Answer 124

A

First, the anti-skid system has a detection system that senses the moment a wheel stops rotating, which it interprets as meaning that the wheel is off the ground (hydroplaning).

Once it senses that the wheel is not rotating, the anti-skid system releases brake pressure in
the brake-metering/modulating valve system to release the brake pad from the brake wheel plate and therefore reinitialize wheel spin.

Answer 125

A

An antiskid system protects against the following:

Locked wheel. This can sometimes occur very rapidly, especially on
a wet or icy runway with a lightly laden aircraft, due to excessive
brake pressure for the prevailing conditions.
Wheel skid/slip
Hydroplaning/aquaplaning
Touchdown. An anti-skid circuit maintains zero brake pressure prior to
touchdown, which thus protects against locked wheels at touchdown.

Answer 126

A

Cabin pressure is measured as a differential between the ambient atmospheric air pressure outside the aircraft and the air pressure inside the cabin.

This pressure measurement is known as differential
pressure, e.g., 8.21 psi. The cabin pressure is normally greater than the external atmospheric pressure, and therefore, the cabin is often referred to as being blown up.

The differential pressure value relates to the pounds per square inch force on the inside of the fuselage
pushing outward.

Answer 127

A

Aircraft (cabin) pressurization is controlled by the cabin’s outflow air valve.

Answer 128

A

10,000 ft.

Answer 129

A

Normal selected on a pilot’s oxygen mask delivers a sea-level pressure mixture of oxygen and ambient cabin air on demand.

Answer 130

A

100% oxygen on demand is used for life-support reasons to maintain the partial pressure of oxygen at or near sea-level pressure.

Sea-level atmospheric pressure is 14.7 psi, and 21 percent of the atmosphere is
oxygen;

therefore, sea-level oxygen pressure is 3.08 psi.
It is not practical to keep the aircraft at the atmosphere’s sea-level pressure of 14.7 psi, but it is practical to increase the percentage volume
of oxygen, thereby maintaining sea-level oxygen partial pressure.

Answer 131

A

100% emergency oxygen is pure oxygen supplied continuously under
positive pressure.

It is used

For life-support conditions above 34,000 ft.
For medical conditions, especially suspected hypoxia
Whenever smoke and/or other harmful gases are present in the cabin

Answer 132

A

First, a green disk on the aircraft’s fuselage is blown out whenever excess pressure occurs in the crew’s oxygen cylinder.

Second, oxygen pressure gauges in the cockpit will indicate below normal or zero on
most system types.

Answer 133

A

14,000 ft.

Answer 134

A

The passenger oxygen system is activated either by the flight crew manually automatically by a barometric pressure controller that releases locking pins that allow the masks to drop from their overhead
compartment whenever it senses a 14,000-ft cabin altitude.

When a passenger pulls on one of the masks (attached to an individual oxygen generator), an electrical firing mechanism mixes the chemical agents that generate the oxygen, which is then supplied continuously
to all the attached masks until the system is emptied.

Answer 135

A

For an individual flight, there must be enough oxygen in the crew system to allow for a 15- to 20-minute descent (i.e., cruise altitude down to 10,000 ft), plus enough oxygen for the rest of the flight to the
nearest diversion airport based on a worst-case scenario.

In addition, there must be enough passenger oxygen for a 15- to 20-minute descent, plus enough oxygen for 10 percent of the required amount for the rest of the flight to the nearest diversion aerodrome based on a worst-case scenario.

Answer 136

A

The elements required for a fire are

(1) oxygen,
(2) a combustible material (fuel), and
(3) an ignition source (heat).

Answer 137

A

Remove its oxygen supply.

Answer 138

A

Bromochlorodifluoromethane (BCF). BCF is a liquefied gas agent that vaporizes on deployment.

Answer 139

A

Bromochlorodifluoromethane (BCF) is stored in

1 - signal red.
2 - purple-brown.
3 - green containers.

Answer 140

A

Water drains in fuel tanks.
Fuel heaters, typically used with gas turbine engines, are used to heat the fuel and evaporate the water prior to delivery to the
engines.
Atmosphere exclusion in the fuel tanks.

Answer 141

A

Specific gravity (SG) of a substance is the ratio of the weight of a unit volume of the substance to the weight of the same volume of water under the same conditions of temperature and pressure.
1 liter of fresh water weighs 1 kg = SG 1.0
1 liter of jet A1 fuel weighs 0.8 kg = SG 0.8

Answer 142

A

The specific gravity of a substance varies with its density, which in turn varies inversely with its temperature.

That is, as temperature
increases, the SG decreases.

Answer 143

A

The quantity of fuel on board an aircraft usually is measured in terms of its mass,

i.e., in either kilograms (kg) or pounds (lb).

By using the SG, you can calculate the mass of a given volume of fuel and vice versa.

Answer 144

A

Fuel is not measured in terms of a volume because a volume of fuel will increase with a temperature rise and, more important, will decrease with a temperature drop.

However, with a rise in temperature, the specific
gravity decreases, and with a drop in temperature, the specific gravity increases, which ensures that the indicated mass (weight) of fuel remains the same.

Obviously, if fuel were uploaded in terms of a volume under high temperature
conditions and a change in temperature reduced the volume
of fuel before or during a flight, then a situation could exist
whereby the aircraft had insufficient fuel to complete the journey.

Answer 145

A

The following procedures should be carried out:
1. Before fueling commences, fueling zones should be established.

Within these zones, the following restrictions should be enforced:
a. No smoking.
b. No auxiliary power unit (APU)
Note: If the APU is on prior to refueling, then it is safe to leave the APU running during refueling.
c. Ground power units should be located as far away as practical
d. Fire extinguishers should be located so as to be readily accessible.

During fueling, the aircraft should be earthed and bonded to the fueling equipment.
Note: For over-wing gravity refueling, the hose nozzle should be bonded to the aircraft structure before removing the tank filler cap.

For pressure refueling, the tank pressure relief valves, where fitted,
should be checked if possible, and the fuel hose bonding lead should be connected before attaching the fueling nozzle.

Passengers embarking and disembarking the aircraft during fueling operations should do so under supervision, and their route should avoid the refueling zones.

Answer 146

A

A deicing system is one in which ice is allowed to build up on a surface and is then removed,

e.g., with pneumatic leading-edge boots.

Answer 147

A

An anti-icing system is one in which ice is prevented from building up on a surface,

e.g., thermal or electrical anti-icing systems on engine
cowls.

Answer 148

A

The purpose of heating the windows is to prevent them from becoming brittle from low temperatures and breaking in a bird strike.

Answer 149

A

Electricity is the movement of electrons (electromotive force and current)
that produces a power.

Answer 150

A

A volt is a unit of electrical force/pressure (expressed as a V). Volts are a measure of

Electromotive force (EMF), i.e., the electrical pressure available from a source of electrical energy used to produce electron flow (current).
Potential differences (pd) in the EMF level between any two circuit points that creates an electrical pressure, which can produce electron
flow from the less positive to the more positive circuit point.

Answer 151

A

A voltmeter indicates the number of volts produced by an electrical
source, e.g., a generator, or the potential difference in a system
between any two points, e.g., a transformer.

Answer 152

A

An amp (ampere) is a unit of electric current (expressed as an I), i.e., the number of electrons flowing in a circuit when an electrical pressure/force (volts) is applied.

Answer 153

A

An ammeter indicates the number of amps/ampere (quantity of electrons
flowing in a current) in an electric circuit.
Note: A quantity of amps is often referred to as a current.

Answer 154

A

An ohm is a unit of electrical resistance (expressed by the symbol R),
i.e., the degree of resistance or opposition to current flow (or amps).

Answer 155

A

An ohmmeter measures and indicates the amount of ohms (electrical
resistance) to the electric current.

Answer 156

A

A watt is a unit of electrical power (expressed by the symbol P), where the electrical power (watt) is a product of the volts and amps being used in the electrical circuit.

That is, 
Watts = volts X amps
Note: 1 kilowatt (1 kW) = 1000 W
1 horsepower (1 hpj = 746 W (modern engines are measured by
horsepower)

Answer 157

A

A wattmeter measures and indicates the number of watts (electrical
power) being consumed.

Answer 158

A

A series circuit is one in which there are no junctions or branches, just
one circuit path.

Answer 159

A

A parallel circuit is one in which there are two or more alternative paths that subsequently reunite.

A feature of this arrangement is that the total current is shared between the parallel circuit paths at its first junction and then restored to a single value at a second junction.

The word parallel is also applied to the way electrical sources, resistors, and loads are connected to different circuit paths (branches).

In this way, the failure of one device is somewhat isolated and does not
affect them all.

Answer 160

A

A fuse is a piece of wire with a low melting point that is placed in series with the electrical load and either melts, blows, or ruptures when a current with a higher value than its ampere rating is placed on it, thus
protecting the electrical load/equipment from excessive power surges.

Answer 161

A

There should be a minimum of 10 percent (or at least three) spare fuses
of the total number of each rated fused installed.

Answer 162

A

Circuit breakers (CBs) are thermal devices placed in series with an electrical load.

They open circuit and thus cut off the electrical equipment when they experience an abnormal (overload) current operating condition.

Open-circuit conditions are indicated by a CB reset push button being visible on a CB panel.

Pressing the CB button in will reengage
and complete the circuit.

Answer 163

A

A non-trip-free circuit breaker can be held in under a fault condition as an emergency measure to complete the circuit and engage the electrical load.

Answer 164

A

A trip-free circuit breaker will not make any internal contact by pressing
the reset button with an overload condition in the electric circuit.

Answer 165

A

Direct current (dc) electrical power flows in only one direction around a circuit and has no appreciable variation in its amplitude.

Answer 166

A

An aircraft’s typical sources of dc electrical power are

Dc generator
Battery
Ground de supply
Rectifier (changes ac to dc)

A transformer-rectifier unit (TRU) changes ac to dc and changes its
voltage level.

Answer 167

A

A battery uses chemical action to separate electrons from their parent atoms and thus generate dc electricity.

The material contained in battery cells determines the voltage output, whereas the amount of current depends on the size of the plates that store the electric current.

Answer 168

A

A primary cell battery uses up the chemicals that produce the electrical energy.

Eventually, the cell runs out of one or more of the chemicals, and the battery is said to be discharged.

Answer 169

A

A secondary cell battery can reverse the chemical changes that take place in its discharge.

The secondary cell can convert electrical energy
back into chemical energy, which is known as charging.

This reconverted chemical energy can then be used to create electrical energy.

By careful handling, a secondary cell can be charged and discharged many times.

Answer 170

A

Alternating current (ac) continuously reverses its direction of flow in an electric circuit.

The complete reversal of current flow is known as a cycle and occurs very rapidly.

Note: 1 cycle per second is called a hertz.

Answer 171

A

The advantages of ac power are as follows:

l. Ac generators (alternators) are simpler and more robust in construction than the dc machines.
2. The power-to-weight ratio of ac machines is much better than that of comparable dc machines.
3. The supply voltage can be converted to a higher or lower value with great efficiency using transformers.
4. Any required dc voltage can be obtained simply and efficiently by using transformer-rectifier units (TRUs).
5. Three-phase ac motors can be operated from a constant frequency source (alternator).

Ac generators do not suffer from commutation problems associated with dc machines and consequently are more reliable, especially at
high altitudes.
High-voltage ac systems require less cable weight than comparable
power low-voltage dc systems.

Answer 172

A

The typical sources of ac electrical power for an aircraft are as follows:

l. Ac generators (alternators), either engine, APU, or ram air turbine (RAT) driven.
2. Inverters (converts dc to ac). Static inverters produce constant frequency ac power.

Rotary inverters produce power for frequency wild
ac systems.

Ground ac supply.
Transformers (change the ac voltage level).

Answer 173

A

A transformer is an electrical device without any moving parts that uses magnetic induction between two windings, known as the primary (input) and secondary (output) coils, to increase or decrease the alternating current.

Answer 174

A

Constant-speed drive units (also known as a generator drive) maintain the ac frequency output of an alternator, normally, to 400 Hz.

Answer 175

A

The basic constant-speed drive unit (also known as a generator drive) consists of an engine-driven hydraulic pump that drives a hydraulic
motor, which itself drives the alternator.

Most CSD units are capable of maintaining the alternator output frequency to within 5% of
400 Hz.

The CSD unit can be disconnected from the engine input drive in the unlikely event of a malfunction.

This allows both the drive unit and the alternator to become stationary, thus eliminating any chance of a
malfunction affecting the engine.

Answer 176

A

The constant-speed drive (CSD) unit can be disconnected at any time, but re-connection can only be done manually on the ground following
shutdown of the engine.

Answer 177

A

Static electricity has the potential to create a spark, inducing a fire risk and/or creating radio interference, if it is allowed to build up in a section of an aircraft.

Answer 178

A

Bonding prevents any part of the aircraft from building up static electricity.

Bonding is the joining by flexible wire strips of each part of the aircraft’s metal structure or metal components to each other, thus providing an easy path for the electrons to move from one part of the
aircraft to another.

Static wicks are fitted to the trailing of the aircraft
surfaces to dispense static electricity into the atmosphere, thus reducing the risk of flash fires and radio interference.

Answer 179

A

The basic parameters of an aircraft’s electrical system are
1. No paralleling of the ac sources of power.

All generator bus sources have to be manually connected through the movement of a switch that also will disconnect any previously existing source.

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6 - Aircraft Instruments and Systems Flashcards

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