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Tech Questions > Aircraft Instruments and Systems > Flashcards

Aircraft Instruments and Systems Flashcards

1
Q

What are the pressure flight instruments? (3)

A

ASI

Altimeter

VSI

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2
Q

How do pressure instruments work in general?

A

Pressure instruments work by measuring Static and Pitot pressure which provides us with the dynamic pressure.

Total / Pitot pressure = Static + dynamic pressure

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3
Q

How does an ASI work?

A

An ASI works by measuring the difference between the pitot pressure within the capsule and the static pressure within the case. The Pitot pressure - static pressure provides us with the dynamic pressure which is represented as IAS. An ASI is calibrated in ISA conditions at MSL and therefore needs to be corrected to provide us with TAS.

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4
Q

What are the ASI errors?

A

Pressure / Position error

Instrument error

Manoeuvre

Compressability error (IAS >300KTAS)

Density error

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5
Q

How is VMO displayed on an ASI?

A

A red / black striped pointer (barbers pole).

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6
Q

Describe how a Machmeter works?

A

A machmeter compares the aircrafts TAS to the LSS.

It has 2 capsules, one altitude capsule and one airspeed capsule.

The first capsule is the airspeed capsule which measures pitot pressure (total pressure), the second is the Altitude capsule whixh expands and contracts depending on the static pressure within the case.

From the formula MN = TAS / LSS we can see that:

MN is proportional to: Dynamic Pressure / Static Pressure which = Pitot - Static (Dynamic) / Static pressure.

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7
Q

What errors does a Machmeter have?

A

Position / Pressure error

Instrument

Manoeuvre

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8
Q

What are the ASI / Mach Meter indications and actions for a blocked pitot or static probe?

Constant alt?

Pitot climb / desc?

Static climb / desc?

A

At a constant altitude they will read the same.

Pitot blockage: Underread in descent / Overread in ascent.

Static blockage: Overread in descent / Underread in ascent.

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9
Q

What are the three different types of altimeter?

A

Simple:

Static pressure is fed in to the instrument case and as the aircraft climbs, an anneroid capsule expands and pushes up a “leaf spring” which controls the pointer via a linkage. It can be adjusted to zero or airfield elevation but does not have a subscale.

Sensitive

This works on a similar principle to the simple altimeter but uses more than 1 anneroid capsule as well as jeweled bearings which reduces the lag. A pressure subscale can also be set on this altimeter.

Servo Assisted

The principle of this is that small movements of the capsules are detected by a very sensitive electro-magnetic pick off (EI bar) which produces a current and is amplified. This reduces instrument error and reducing lag, allowing it to feed into other systems such as the autopilot etc.

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10
Q

What are the altimeter instruments errors?

A

Position

Instrument

Manoeuvre

Barometric (Calibrated for ISA)

Lag

Temperature (Calibrated for ISA)

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11
Q

What are the altimeter indications / actions for blocked static port?

A

The altimeter will display the the altitude where the blockage occured and will remain there regardless of any change in altitude.

Ensure pitot heat is on or use the alternate static source.

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12
Q

How does a VSI work?

A

A VSI measures the present static pressure with a recent static pressure. Each side of a metering unit through a restricted choke which transmits the change at a lower rate.

This shows the difference in static pressure inside the capsule as well as inside the case.

As there is more feet per hPa at altitude the rate of pressure change would be different at different altitudes. This is corrected by an orifice which provides a constant rate of change regardless ofaltitude.

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13
Q

What are the errors of the VSI?

A

Position

Instrument

Manoeuvre

Lag (6 seconds)

Blockage (crack glass if need to, if alt static source is selected there will be a momentary climb)

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14
Q

How does an IVSI work?

A

An IVSI works by incorporating a “dashpot” or a “dynamic vane” which responds very quickly to change in altitude due to the inertia. This causes and instant rise or reduction in the pressure of the capsule.

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15
Q

What are the disadvantages of an IVSI?

A

When applying a larger angle of bank such as 40 degrees or more the IVSI will indicate a climb.

The IVSI is also very sensitive when in turbulent conditions.

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16
Q

What is the indication of a blocked static port?

A

A blocked static port would mean that the value of the static pressure inside the capsule as well as the case would be the same and therefore would indicate zero on a VSI.

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17
Q

What are the two types of thermometers? (2)

A

Direct Reading:

(bimetallic strip) made from brass and invar

Total Air Temperature probe:

This is fitted away from the aircrafts boundary. As the air passes through the tube, separation of water partucles is achieved by hving the airflow turn at right angles before passing the sending element.

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18
Q

What are the errors of air temperature gauges? (3)

A

Instrument error (imperfections)

Environmental errors (solar heating / ice accreation)

Heating error (adiabatic / compression)

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19
Q

What is the TAT formula?

A

TAT = SAT + RR

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20
Q

What is the recover factor? (Kr)

A

The percent of the ram rise recovered by the TAT probe.

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21
Q

How does an Air Data Computer (ADC) work?

A

An ADC uses analogue or digital computing techniques to convert pressure and temperature data into electrical signals which are transmitted to the display instruments and other systems.

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22
Q

When an ADC has a failure? What does it use to give a prompt indication?

A

BITE (Built In Test Equipment)

Power up BITE (start up)

Continuous BITE (every second)

Maintenance BITE (current or post failure for maintenance crew)

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23
Q

What are the advantages of an ADC?

A

Improved displays

Reduced lag

Error correction

Integration

Clean design

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24
Q

What is a Gyro?

A

A gyroscope consists of a rapidly spinning disc (4,000-25,000 rpm) which has 2 basic properties, rigidity and precession.

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25
Q

How does a gyroscope work?

A

A gyroscope maintains its rigidity in space by the inertia of its spinning mass, unless subject to an external force. The rotor is usually susended in a series of frames called gimbals, 1 gimbal = 1 degree of freedom. Any force applied to the gyro will create precession 90 degrees in the direction of rotation. The rigidity of a gyroscope depends on the mass of the rotor, the effective radius of the rotor as well as the rpm of the rotor.

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26
Q

What are the two types of gyroscopic wander?

A

Horizontal = drift

Vertical = topple

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27
Q

Describe Real / Apparent wander?

A

Real (random) wander: This is where the axis of the gyro moves with respect to inertial space. For example, manufacturing imperfections and bearing friction etc which are reduced by higher quality engineering.

Apparent wander (Earth Rate and Transport Wander):

Earth Rate - this is caused by the rotation of the earth. At the equator the gyro axis remains fixed in space and aligned to the local meridian. At the pole the gyro still remains aligned in space but the meridian direction changes as the earth rotates at the following rate with a negative value in the northern hemisphere:

Earth Rate = 15 x sine mean latitude

Transport Wander:

This is caused by flight east or west at latitudes other than the equator and is actually meridian convergence.

Transport Wander = (GS / 60) x tan mean latitude

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28
Q

What are the two main type of gyros? (2 main, 1 has 3 subtypes)

A

Displacement Gyros:

These have 2 gimbals and 2 degrees of freedom (DGI / AI)

Rate Gyros:

These have 1 gimbal and 1 degree of freedom (Rate of turn Indicator / Yaw dampers)

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29
Q

Describe the directional gyro indicator (DGI)?

Type of gyro?

Tied to what plane?

How many gimbals?

Advantages?

Errors? (5)

A

The DGI uses a tied gyroscope in the yawing plane and has 2 gimbals. It needs to be regularly synchronised with the magnetic compass and is not to replace it but compliment it.

It’s advantages are that it does not suffer from acceleration errors or other magnetic errors caused by the earths magnetic field.

However it does suffer from:

  • Transport error
  • Earth Rate
  • Random wander
  • Gimballing error
  • Errors from varying RPM
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30
Q

How is apparent wander corrected for on a DGI? (2)

A

This depends on how sophisticated the instrument is but principally it is correted by 2 methods:

Every 10 to 15 minutes manually synchronise with the magnetic compass using the slaving knob on the DGI.

Use of a latitude nut which provides an opposite error to the earths rotation (ER = 15 x sine mean latitude per hour).

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31
Q

What is transport wander on an uncorrected gyroscope on a DGI?

A

Transport Wander = Groundspeed / 60 x tan mean latitude

This is effected by the aircraft east / west position on the globe.

Transport Wander + Apparent Wander = Total Apparent Wander

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32
Q

Describe the air driven artificial horizon?

How many degrees of freedom and what are they?

Axis of gyroscope and what gyroscope?

How is gyroscopic precession overcome?

A

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

There are 2 degrees of freedom (pitch and roll)

Uses an earth tied gyroscope which is alligned to the earths vertical axis and rotates about a vertical exis.

4 pendulous vanes are used in order overcome gyroscopic precession.

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33
Q

What errors do the artificial horizon have?

A

Turning errors (main)

Acceleration errors

Real wander of gyro

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34
Q

What are the turning errors of the Artificial Horizon?

A

Through 90: Under read bank - Pitch climb

Through 180: Correct bank - Pitch climb

Through 270: Over read bank - Pitch climb

Through 360: Correct bank - Pitch correct

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35
Q

What are the indications of a failed air driven artificial horizon? (2)

How do you re-erect the gyro?

A
  • Low suction shown on the suction gauge.
  • Possible warning flag

To re-erect the gyro can be accomplished by caging and uncaging the gyroscope, but if there is low suction then it will probably topple again and the VSI and turn coordinator should be monitored.

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36
Q

Describe the electrically driven artificial horizon?

Type of motor?

Speed in RPM?

Advantages?

What is its freedom in pitch and roll in degrees?

A

Electrically driven artificial horizons have the same basic principles as the air driven one, with the earth tied gyro and 2 gimbals (pitch and roll).

However, with use of a squirrel-cage motor, the gryoscope is driven to a higher RPM of around 22,000 RPM which increases its rigidity and means that it does not require pendulous suspension as well as minimising turning and acceleration errors.

It has complete freedom in roll and around 85 degrees in pitch.

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37
Q

What is a servo assisted artificial directional indicator (ADI) or also known as a remote artificial horizon?

Advantages? (3)

A

This uses data from the INS / IRS systems to display pitch and roll information in modern aircraft.

The advantages of this system is that it is free of turn and acceleration errors. Also, it uses a dual system whereby INS 1 feed the captain’s instruments and INS 2 feeds the co-pilots instruments which can be compared to separate standby insturments in order to detect errors and deselect incorrect systems.

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38
Q

Describe the turn and slip coordinator?

What type of gyro does it use and what axis it it fixed to?

A

A turn and slip coordinator allows accurate rate 1 or 2 turns and shows if the aircraft is “skidding” or “slipping”.

It uses a rate gyro in order to measure the rate of turn about a vertical axis which is fixed to the aircraft lateral plane.

The gimbal is pivoted on the aircraft fore and aft axis and compresses or extends a spring which moves a needle that indicates the rate of turn.

39
Q

What is looping error?

A

If the aircraft is then rapidly pitched nose up (in a loop or recovery from a spiral dive) this pitch input can deflect the gyro to read maximum turn rate. Therefore if there is excessive g loads on the aircraft the instrument will over read.

40
Q

What is the formula for rate one turns between 100 and 250 knots TAS?

A

TAS / 10 + 7 = R1

41
Q

What is a turn co-ordinator?

A

The turn co-ordinator is an interesting development of the turn and slip indicator. The is spring restrained still but is mounted about 30 degrees with the aircraft longitudinal axis which makes the gyroscope sensitive to banking also.

42
Q

Describe the earth’s magnetic field?

A

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

These poles are not the same as the geographic poles and therefore there is an angular distance between them which is known as variation.

43
Q

What is magetic dip?

A

Magnetic dip is the vertical component of the magnetic field over the surface of the earth.

The horizontal force which is known as the directive force is what alligned the magnetic compass needle with the magnetic meridians. This force gets weaker towards the magnetic poles while the value of the dip Z increases.

Therefore over the magnetic poles the magnetic compass is useless.

44
Q

What is compass swinging?

When should it be swung? (10)

A

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

It should be swung:

  • New compass
  • Aircraft modification with large ferrous metal
  • Electrical modifications
  • Doubt of compass
  • Struck by lightening
  • Exposed to a shock (hit)
  • Carrying unusual ferrous payload
  • Maintenance inspection
  • Large change of magnetic latitude
  • Aircraft has been in long term storage
45
Q

What are the errors of a magnetic compass? (2)

A

Turning errors (UNOS / ONUS)

Acceleration / Deceleration errors

46
Q

What comprises the remote indicating magnetic compass system? (6)

A

A remote indicating magnetic compass which comprises of the following:

  • A flux valve
  • Heading indicator (compass)
  • Precession amplifier
  • Precession motor
  • Horizontal gyro
  • Rapid synchronisation facility
47
Q

What is an RBI?

A

An RBI is a simple ADF that is used to display an NDB.

The pilot can add the relative bearing of the aircraft to the heading to work out the QDM to the NDB.

The later versions of the RBI have a moving card where the QDM is simply read from the tail of the ADF needle.

48
Q

What is an RMI?

A

An RMI is used to display ADF or VOR navigation information and is an advance of the RBI.

49
Q

What is an OBI?

A

Used for VOR navigation and the cheapest way to do so, has a manual compass card that selects the desired VOR radial and a CDI needle to provide a steering aid to place the aircraft on that radial, with a “TO/FROM” indicator to resolve directional ambiguity.

50
Q

Describe the HSI instrument?

A

The HSI is a sophisticated navigation instrument which combines the directional gyro and the NAV indicator into one instrument. This reduces pilot workload by providing heading, course reference, course deviation and glide slope information - all in one visual aid. In addition, an HSI makes it easier to visualise the aircraft’s position with reference to the selected course or holding patterns.

51
Q

What does EFIS stand for?

A

Electronic Flight Information System

52
Q

What is an EFIS?

What are its components (5)

A

EFIS is a fully integrated, computer based, digital navigation system that displays information on CRT screens called EADI (elecrtonic additude directional indicator) and EHSI (electronic horizontal situational indicator).

Components

  1. EHSI or nav display
  2. EADI
  3. Symbol Generator
  4. Control Panel
  5. Remote Light Sensor Unit
53
Q

What is the advantage of an EFIS flight deck?

A

There are two distinct advantages:

  1. It displays data in a clearer and more versatile manner.
  2. Can bring together various sources of data to present the pilot with the best possible attitude and navigation information.
54
Q

What is typically displayed on the EADI (Electronic Attitude Director Indicator)? (10)

A

Attitude

Additional attitude information such as “eye brows” and FD and rising runway

Turn and slip (from IRS)

Altitude

Radio Altimiter

DH / DA

IAS

GS / Mach number

VNAV or Glideslope / LNAV or Localiser

Autopilot Annunciators

55
Q

At what height would you expect the rising runway to become active on the EADI?

A

200 feet RA but is type specific

56
Q

What are the EHSI (Electronic Horizontal Situation Indicator) display modes? (7)

A

FULL VOR / ILS

FULL NAV

EXPANDED VOR / ILS

EXPANDED NAV

MAP MODE

CTR MAP MODE

PLAN

57
Q

Which EHSI modes can display weather radar? (4)

A

Expanded VOR / ILS

Expanded NAV

Center Map Mode

Map Mode

58
Q

What are the generic EFIS colour codes?

  • Green
  • White
  • Magenta
  • Cyan
  • Red
  • Yellow
  • Black
A
  • Green - Active modes
  • White - Present situation
  • Magenta - Command information
  • Cyan - Non active background information
  • Red - Warning
  • Yellow - Caution
  • Black - Off
59
Q

What is TCAS and how does it work?

Type of advisories?

When they are inhbited?

What plane is the RA?

What principle?

A

Traffic Collision Avoidance System and works by using aircrafts SSR transponders and providesthe pilots with traffic information and manoeuvre advice.

Initially a traffic advisory (TA) is issued with no manoeuvre advice.

If there is a collision threat then a resolution advisory (RA) is issued with manoeuvre advice but only in the pitching plane.

RA’s are inhibited below 500’ and TA’s are inhibited below 400’.

60
Q

What is ADS-B and how does it differ from TCAS?

A

ADS-B (Automated Dependent Surveillance - Broadcast) is a traffic avoidance system which incorporates cockpit display of traffic information and is overall more capable than TCAS.

It uses ATC transponders to transmit aircraft information to the ground, using the Mode S 1090 MHz Extended Squitter with a refresh rate of 0.5 seconds.

On aircraft, it is the TCAS computer that receives and treats the ADS-B information coming from ATC transponders of surrounding aircraft. The information is then displayed on the Navigation Display (ND)

61
Q

What information is typically shown on ASD-B? (7)

A
  • Aircraft identification
  • Bearing/Distance
  • Heading/Tracking
  • Wake vortex category
  • Relative altitude/Absolute altitude
  • Ground speed
  • Vertical velocity
62
Q

What is GPWS and how does it work? (7)

A

Ground Proximity Warning System

This uses various data inputs in order to detect if any of the attached potentially dangerous circumstances occur.

The system provides the pilot with an aural and a visual alert.

This system is mandatory on aircraft greater than 5700Kg.

63
Q

What are the GPWS warnings? (7)

A

See attached

64
Q

What is the difference between GPWS and EGPWS? (2)

A

The EGPWS “look ahead” and has a terrain threat display.

In a GPWS mode 2 depends on the steepness of the terrain.

65
Q

What is the purpose of the FMS? (3)

A

The Flight Management System is designed to improve navigation, aid fuel efficiency and to reduce crew workload.

Computers are used to fly the aircraft along complex routes using LNAV and VNAV.

The managed data can be used to: 1) advise the pilot or, 2) to control the autopilot / autothrottle.

66
Q

What are the 5 sources of information for the FMS? (5)

A

Navigation / performance databases

Navigation aids (VOR, DME, GPS, IRS)

Engine fuel

ADC

CDU

67
Q

What are the LNAV and VNAV flight management computer functions?

A

The LNAV and VNAV functions are custom made routes stored in the performance and navigation databases within the FMC. The company flight plan will be stored in this and can be amended by the pilots via the CDU of necessary.

68
Q

What are single axis, two axis and three axis autopilots?

A

Single axis: Roll axis.

Two axis: Roll and Pitch axis.

Three axis: Roll, Pitch and Yaw Axis.

69
Q

How quickly does an autopilot respond to changes compared to a human pilot?

A

Human pilot can take up to 200 milliseconds.

Auto pilot can take up to 50 milliseconds.

70
Q

What are the various autopilot modes of operation? (8)

A
  1. HDG
  2. ALT HOLD
  3. LNAV
  4. VNAV
  5. VORLOC
  6. APP
  7. LVL CH
  8. VS
71
Q

What is a flight director system?

A

A flight director system is a system built into the FMC whereby it provides guidance to the pilot displayed on the (E)ADI without any automatic input from the servos.

72
Q

What are the rrors of a flight director? (2)

A
  1. Interpretation of the FD bars.
  2. It is configured with the autopilot system which reacts extremely quickly which ca lead to overcorrections on the approach.
73
Q

Describe an autoland system?

A

An autoland system is a function of the autopilot flight director system and the autothrottle system that is activated using approach mode on the MCP.

The autothrottle is also used by the autoland system and is used to correct or maintain airspeed through engine power changes in the approach, flare and will auto disconnect on touchdown.

74
Q

What is a multiplex autoland system?

A

A multiplex autoland system is a term used for an autoland system that uses 2 or more independent autopilots. This provides redundancy to the system.

75
Q

What is a fail passive / fail operational autopilot / landing system?

A

Fail Passive (land 2 system):

A fail passive autopilot / autoland is whereby there are 2 systems where should one fail the landing is not completed.

Fail Operational (land 3 system):

A fail passive autopilot / autoland is whereby there are 3 systems where should one fail the landing is completed as fai passive.

76
Q

What are the Auto Throttle modes? (5)

A
  1. IAS
  2. IAS / Mach
  3. TO
  4. GA
  5. Max Cont Thrust
77
Q

What is nose wheel shimmy?

A

This is a sinusoidal movement of the nose wheel due to the flexibility of the tire sidewalls. The vibration can cause aircraft damage and wear the wheel bearing, low tyre pressure and wear on the linkages.

78
Q

What are fuseable plugs?

A

Fuseable plugs are found in tubeless wheel hubs and are designed to allow for a controlled blow by allowing air to leak away slowly.

79
Q

What are chimed tired?

A

This is a special type of sidewall design which diverts water away from the intake of rear mounted engines.

80
Q

How does an autobrake system decelerate an aircraft?

A

An automatic braking systimg regulated hydraulic pressure with the use of a metering valve in the hydraulic brake line in order to maintain constant deceleration until the aircraft reaches a complete stop. Typically it has settings of 1,2,3 and Max which is the RTO setting? Typically it monitors the reverse thrust which is more effective at high speeds and applied the autobrakes with ground spoilers / lift dumpers to increase their effectiveness.

81
Q

What effects braking temperature prior to / during take off? (6)

A
  1. Duration of taxi
  2. Aircraft take off weight
  3. Runway slope
  4. OAT
  5. Air pressure
  6. Headwind / tailwind
82
Q

How does an antiskid system work?

A

An anti skid system works by using a detection system which compares the rotation speed of the nose wheel with the speed of the other wheels. Should the rotation speed of those wheels reduce below that of the nose wheel then braking pressure is reduced on those wheels (brake-metering valve system).

83
Q

What are the 4 types of antiskid protection?

A
  1. Touchdown protection
  2. Hydroplane protection
  3. Anti skid
  4. Locked wheel protection (ice etc)
84
Q

How is aircraft cabin pressure controlled?

A

Cabin pressure is controlled by controlling the amount of air that is let out of the cabin using an “outflow valve”.

85
Q

What is electricty?

A

Electricity is the free flow of electrons from one place to another which creates an electromotive force (EMF or Voltage and current).

86
Q

What is an amp a measurement of?

A

Unit of electrical current expressed as I (number of elecrons).

87
Q

How many fuses should be carried on board an aircraft?

A

At least 10% of the number of fuses (at least 3) of each rating installed.

88
Q

What is a trip free / non trip free circuit breaker?

A
  • Trip free circuit breaker: Cannot be held in to create a connection with an overload condition.
  • Non trip free circuit breaker: Can be held in under fault condition as an emergency condition to complete the circuit.
89
Q

What is DC electricity?

A

DC electricity flows in one direction and has no appreciable variation in amplitude.

90
Q

What are the aircraft’s typical sources of DC electricty? (4)

A
  1. DC Generator
  2. Battery
  3. Ground DC supply
  4. Rectifier / TRU (Transformer Rectifier Unit) [AC => DC]
91
Q

What is the difference between a primary and secondary battery?

A

A secondary battery can be re-charged.

92
Q

What is alternating current?

A

This current continuously reverses its direction of flow. A complete direction reversal is known as a cycle. 1 Hertz is the number of cycles per second. Aircraft run at 400 Hz.

93
Q

What are the aircraft’s sources of AC power?

A
  1. AC Generators
  2. Inverters (DC => AC)
  3. Ground power supply
  4. Transformers
94
Q

What do constant speed drive units achieve?

A

CSDU’s maintain a constant AC frequency (400 Hz) by

Tech Questions (5 decks)

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