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ATPL Theory - Module 1 > Instrumentation - Airspeed Indication > Flashcards

Instrumentation - Airspeed Indication Flashcards

1
Q

What increases the accuracy of servo-assisted altimeters compared to previous generations?

A

They no longer rely on a direct mechanical link between the capsules and the height pointers.

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2
Q

What is the role of the I-bar in servo-assisted altimeters?

A

The I-bar transmits movement to a pivoted bar, which affects the voltage output from the E-bar.

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3
Q

How is the voltage difference in the E-bar used in servo-assisted altimeters?

A

The voltage difference is fed to an amplifier and then to a servo motor to reposition the I-bar.

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4
Q

What does the E/I bar system in servo-assisted altimeters describe?

A

It is described as an ‘induction pick-off’ or an ‘electro-magnetic pick-off’.

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5
Q

What type of display is commonly used in servo altimeters?

A

The ‘drum and pointer’ type of display.

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6
Q

What are the main components involved in the internal workings of a servo altimeter?

A

Capsule stack, E/I bar assembly, complex gearing, and a digitiser.

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7
Q

What do fourth generation ADC driven systems use to calculate altitude?

A

They use static pressure sensed by the Air Data Computer (ADC).

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8
Q

How is altitude displayed on modern EFIS displays?

A

On a vertical tape scale, usually to the right of the PFD.

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9
Q

What is the accuracy requirement for altimeters with a test range of 0 to 9000 m according to ICAO?

A

±20 m or ±60 ft

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10
Q

What is the relationship between meters and feet?

A

1 meter = 3.28 feet

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11
Q

What are the two types of QFE settings?

A

Airfield QFE and Touchdown QFE

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12
Q

What does the QNH setting make the altimeter read?

A

Aircraft altitude Above Mean Sea Level (AMSL).

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13
Q

What is the standard setting for altimeters in terms of hPa?

A

1013.25 hPa

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14
Q

How is density altitude calculated?

A

Density altitude = pressure altitude + (120 x ISA deviation).

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15
Q

What is position error in altimeters?

A

An error that affects the altimeter readings, varying with TAS and angle of attack.

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16
Q

What is barometric error in altimeters?

A

An error due to changes in sea level pressure from the datum set on the altimeter subscale.

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17
Q

What is temperature error in altimeters?

A

An error due to differences in air mass temperature from the international standard atmosphere.

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18
Q

How can temperature corrections be applied for altimeter readings?

A

Using temperature correction tables for specific heights and altitudes, particularly in very low temperatures.

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19
Q

What happens if the static line becomes blocked in an altimeter system?

A

No change in altitude will be displayed.

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20
Q

What does a pressure operated Vertical Speed Indicator (VSI) measure?

A

The rate of change of static pressure, displayed as rate of climb or descent.

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21
Q

What is the key component of the metering unit in a simple VSI?

A

A “choke” directing air through a capillary tube and a “knife edge orifice.”

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22
Q

How does an Instantaneous VSI (IVSI) differ from a standard VSI?

A

It includes weights in dashpots to provide immediate differential pressure, countering the lag in indication.

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23
Q

What units are rates of climb and descent commonly shown in?

A

Feet per minute (ft/min) and sometimes meters per second (m/s).

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24
Q

What are the three systems for finding vertical speed?

A

Strap-down Inertial Reference System (IRS), Air Data Computer (ADC), and dynamic vane VSI.

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25
Q

How do modern EFIS displays show vertical speed?

A

To the right of the altitude indicator strip.

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26
Q

What causes instrument lag in basic vertical speed indicators?

A

The time taken for the pressure difference to build up between the capsule and the case.

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27
Q

What is indicated airspeed (IAS)?

A

Airspeed measured by the aircraft’s instruments, reflecting dynamic pressure.

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28
Q

How can true airspeed (TAS) be calculated from indicated airspeed (IAS)?

A

By considering the air density; TAS is higher than IAS at altitude due to lower air density.

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29
Q

What is the Mach number?

A

The speed of the aircraft as a proportion of the speed of sound.

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30
Q

How is airspeed commonly referred to in aviation?

A

In knots (KT), nautical miles per hour. Less commonly, in statute miles per hour (mph) and kilometers per hour (km/h).

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31
Q

What was the earliest method of measuring dynamic pressure for airspeed?

A

Using a flat plate indicator attached to the wing struts of a biplane.

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32
Q

What is a mechanical Air Speed Indicator (ASI)?

A

An instrument that uses pitot and static pressure to indicate airspeed, calibrated at sea level under ISA conditions.

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33
Q

How do ADC driven instruments calculate airspeed?

A

By using sensed pressures from pitot and static lines, calculated by the Air Data Computer (ADC) using Saint-Venant’s formulae.

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34
Q

What can affect the altimeter readings due to position error?

A

Position error can be minimized by good design but generally varies with TAS and angle of attack.

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35
Q

How do sophisticated mechanical altimeters overcome instrument errors?

A

Instrument errors caused by friction in the gearing are overcome by the means discussed for more sophisticated mechanical altimeters.

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36
Q

What is hysteresis error in altimeter readings?

A

Hysteresis error occurs because aneroid capsules are not perfectly elastic and can be reluctant to change shape after being at one pressure for a period of time.

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37
Q

How can barometric error in altimeter readings be removed?

A

Barometric error can be removed by adjusting the subscale to the correct value.

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38
Q

Why must temperature corrections be applied to altimeter readings?

A

Temperature corrections must be applied because the altimeter may overread or underread depending on the air temperature, especially at very low temperatures and near the ground.

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39
Q

What happens if the static line becomes blocked?

A

The pressure inside the instrument cannot change, and no change in altitude will be displayed.

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40
Q

What are the three pressure datums for setting an altimeter?

A

QFE, QNH, and standard setting (1013.25 hPa or 29.92 inches of mercury).

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41
Q

How is QFE measured?

A

Airfield QFE is measured at the highest point of the airfield surface, and Touchdown QFE is measured at the touchdown of the runway for precision approaches.

42
Q

What does QNH subscale setting indicate on an altimeter?

A

It makes the altimeter read aircraft altitude above mean sea level (AMSL) and shows airfield elevation AMSL on touchdown.

43
Q

What is the density altitude?

A

The pressure altitude corrected for temperature, giving the same air density as the prevailing non-ISA combination of temperature and pressure altitude.

44
Q

What is the vertical speed indicator (VSI)?

A

An instrument that shows rates of climb and descent.

45
Q

How does a simple VSI measure the rate of climb or descent?

A

It records the rate of change of static pressure and displays it as a rate of climb and descent using a capsule fed with static pressure in a case also fed with static.

46
Q

What is the function of the metering unit in a VSI?

A

The metering unit controls the flow of air through the capsule and case to maintain differential pressure, compensating for pressure altitude and temperature.

47
Q

How does an Instantaneous VSI (IVSI) work?

A

It includes weights in dashpots centered with springs to provide an immediate differential pressure as the aircraft starts to climb or descend, reducing the indicated rate of climb or descent as the aircraft levels out.

48
Q

What is the main advantage of an IVSI over a standard VSI?

A

An IVSI shows the rate of climb or descent immediately, while a standard VSI has a lag in indication.

49
Q

How is airspeed measured in aircraft?

A

Airspeed is measured based on dynamic pressure, indicated by IAS (Indicated Air Speed) and TAS (True Air Speed).

50
Q

What is the relationship between IAS and TAS at high altitudes?

A

At high altitudes, the same dynamic pressure reflects a higher true airspeed (TAS) even though the aircraft handles the same as at lower altitudes.

51
Q

What is the Mach number?

A

The speed of the aircraft as a proportion of the speed of sound, Mach 1.

52
Q

How is density altitude calculated using a CRP5?

A

Set pressure altitude against temperature in the AIRSPEED window and read off the density altitude in the DENSITY ALTITUDE window.

53
Q

What is Calibrated Air Speed (CAS)?

A

IAS corrected for instrument and position errors specific to the aircraft.

54
Q

What is Equivalent Air Speed (EAS)?

A

CAS corrected for compressibility error.

55
Q

Why is compressibility correction not needed below certain speeds?

A

FAA documentation states a correction is not required below 200 KT CAS and 10,000 ft, equating to around M0.36 in a Standard Atmosphere.

56
Q

What are the different units of airspeed measurement?

A

Nautical miles per hour (knots, KT), statute miles per hour (mph), and kilometers per hour (km/h).

57
Q

What are the main causes of errors in airspeed indicators (ASI)?

A

Sensor errors, mechanical inaccuracies, or design issues of the instrument.

58
Q

How does air density affect TAS calculations?

A

A correction for air density is required to calculate TAS from EAS. At high altitudes, the TAS can be much higher than IAS/CAS/EAS.

59
Q

What is the QFE setting on an altimeter?

A

The QFE is the subscale setting that makes the altimeter read zero on the ground.

60
Q

What are the two types of QFE available?

A

Airfield QFE and Touchdown QFE.

61
Q

What does Airfield QFE measure?

A

It is measured at the highest point of the airfield surface and is generally correct for the whole airfield.

62
Q

What does Touchdown QFE measure?

A

It is measured at the touchdown of the runway for precision approaches.

63
Q

What does the QNH setting on an altimeter show?

A

It makes the altimeter read aircraft altitude Above Mean Sea Level (AMSL).

64
Q

What are the two types of QNH available?

A

Airfield QNH and Regional or Zone QNH.

65
Q

What is Airfield QNH used for?

A

It gives an altitude AMSL for the position of the aerodrome and must be set on at least one altimeter when departing from an aerodrome in controlled airspace.

66
Q

When is Regional or Zone QNH used?

A

It is the lowest forecast QNH for the next hour within an Altimeter Setting Region (ASR) or Zone Area.

67
Q

What is the standard setting for an altimeter in terms of hPa?

A

1013.25 hPa.

68
Q

How is density altitude calculated on the CRP5?

A

Set pressure altitude against temperature in the AIRSPEED window, then read off the density altitude in the DENSITY ALTITUDE window.

69
Q

What is a Vertical Speed Indicator (VSI)?

A

An instrument that shows rates of climb and descent by measuring changes in static pressure.

70
Q

What is the basic principle of a VSI?

A

It consists of a capsule fed with static pressure in a case also fed with static pressure, indicating rate of climb or descent based on differential pressure.

71
Q

What is an Instantaneous VSI (IVSI)?

A

A VSI that counters time lag in indication by using weights and dashpots to immediately sense differential pressure due to aircraft inertia.

72
Q

What are the three systems for finding vertical speed in modern aircraft?

A

Inertial Reference System (IRS), Air Data Computer (ADC), and dynamic vane VSI.

73
Q

How are rates of climb and descent commonly shown?

A

In feet per minute (ft/min) or meters per second (m/s).

74
Q

What is the relationship between knots and nautical miles?

A

1 knot equals 1 nautical mile per hour.

75
Q

How is the True Air Speed (TAS) calculated from Indicated Air Speed (IAS)?

A

TAS is calculated from IAS by correcting for air density and compressibility.

76
Q

What are the color-coded markings on an ASI for?

A

They indicate different speed ranges, such as flap operating range, normal operating speed range, caution range, and never exceed speed.

77
Q

What does the vertical speed indicator (VSI) show?

A

Rates of climb and descent.

78
Q

Where is the vertical speed indicator positioned in a standard instrument layout?

A

Below the altimeter.

79
Q

How does a simple VSI measure the rate of climb and descent?

A

By recording the rate of change of static pressure.

80
Q

What is the primary component inside a VSI that reacts to pressure changes?

A

A capsule fed with static pressure.

81
Q

How does the metering unit in a VSI function?

A

It directs air through a capillary tube and a knife-edge orifice to maintain differential pressure.

82
Q

What is an IVSI and how does it differ from a simple VSI?

A

An IVSI includes weights in dashpots to counter the time lag in indication.

83
Q

Why might an IVSI not be reliable during steep turns?

A

It can indicate a climb initially and then a descent on rollout due to the load factor change.

84
Q

What unit conversions might be necessary for VSI readings?

A

Feet per minute to meters per second.

85
Q

How can barometric height data be used to determine vertical speed?

A

It can be calculated and displayed as vertical velocity if available electronically.

86
Q

What are the two types of units commonly used for airspeed?

A

Knots (KT) and miles per hour (mph).

87
Q

How is dynamic pressure related to airspeed?

A

Dynamic pressure is a measure used to determine airspeed.

88
Q

What is the formula for dynamic pressure?

A

Dynamic pressure = ½ ρV².

89
Q

Why is True Air Speed (TAS) different from Indicated Air Speed (IAS) at higher altitudes?

A

Because air density decreases with altitude.

90
Q

What is the Mach number?

A

The speed of the aircraft as a proportion of the speed of sound.

91
Q

Why is the Mach number important?

A

As aircraft approach the speed of sound, airflow changes can induce instability and control issues.

92
Q

How is TAS calculated from CAS?

A

By knowing the air pressure and temperature.

93
Q

What is compressibility error?

A

It’s the error caused by air behaving as a compressible fluid at higher speeds, affecting dynamic pressure readings.

94
Q

How do navigation computers handle compressibility corrections?

A

By using formulas to account for compressibility and air density.

95
Q

What does Calibrated Air Speed (CAS) account for?

A

Instrument and position errors specific to the aircraft.

96
Q

How can the airspeed calibration for a Cessna 172 be converted?

A

By using the correction table from Knots Indicated Air Speed (KIAS) to Knots Calibrated Air Speed (KCAS).

97
Q

What does Equivalent Air Speed (EAS) account for?

A

Compressibility error corrections.

98
Q

What type of display might combine both CAS and Mach number?

A

Servo-driven mechanical instruments.

99
Q

What do coloured markings on ASIs indicate?

A

Specific speeds and speed ranges, such as flap operating range and never exceed speed.

100
Q

What is the purpose of pitot static blockages and leaks checks?

A

To ensure accurate airspeed readings and safety during flight.

101
Q

What should be checked before flight regarding the ASI?

A

Ensure all covers and plugs are removed, vents and drain holes are clear, and pitot heaters are on.

ATPL Theory - Module 1 (17 decks)

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