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Module 13 EASA Part 7 Book 1 > Chapter 3 - Pitot/static instruments > Flashcards

Chapter 3 - Pitot/static instruments Flashcards

1
Q

What are the three Q codes?

A

QNE - ICAO standard mean sea level pressure
QFE - Ambient static pressure existing at mean airfield level at any particular time of the day
QNH - Mean sea level pressure at any particular time of day

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2
Q

How does a pilot obtain values for QFE and QNH?

A

ATC

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3
Q

What will show on the instrument when QNH is input while the aircraft is on the ground?

A

Height of the airfield above mean sea level

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4
Q

What should all aircraft instruments be set to above a transition altitude?

A

QNE

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5
Q

How can an approximate true altitude be obtained locally?

A

By setting the altimeter to the local QNH

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6
Q

What is the absolute altitude?

A

Height above ground level (AGL)

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7
Q

What is true altitude?

A

Height above mean sea level (AMSL)

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8
Q

How is absolute altitude calculated?

A

Absolute altitude = true altitude - elevation of the ground

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9
Q

What is the only system capable of directly indicating the absolute altitude?

A

Radar altimeter

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10
Q

What is indicated altitude?

A

Indicated reading which is seldom accurate as standard conditions are rarely met and errors may be present in the instruments and pitot/static systems

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11
Q

What is calibrated altitude?

A

Indicated altitude correct for instrument error and pressure errors

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12
Q

How will increases in temperature affect indicated altitude?

A

Drop in indicated altitude

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13
Q

How will an increase in atmospheric pressure affect indicated altitude?

A

Shows a drop in indicated altitude

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14
Q

What might cause a sensitive altimeter case to misread?

A

The instrument case is sealed, therefore leaks in a pressurised aircraft will cause the instrument to misread (altitude will read lower)

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15
Q

Why is beryllium copper often used as the material of which the stack of three capsules is made within sensitive altimeter cases?

A

Natural springiness of the material

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16
Q

How is capsule elasticity compensated for temperature changes?

A

Invar steel/brass bi-metallic ‘U’ shaped strip around the capsule stack

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17
Q

How is reading of the altimeter dial simplified?

A

Number of different pointer lengths and shapes have been used

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18
Q

What are servo altimeters?

A

Pointer and counter mechanism are driven using a servo (motor) system to overcome torque requirements of operating counter mechanisms

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19
Q

Where is the input excitation supplied in a servo assisted altimeter?

A

AC supply is fed to the centre leg of the ‘E’ bar

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20
Q

How are the secondary coils connected in the ‘E’ bar of a servo assisted altimeter?

A

The voltages in each leg are 180° out of phase and equal and opposite voltages

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21
Q

Why should the pressure setting in a servo altimeter only be moved with electrical power supplied to the instrument?

A

The E&I bar might become out of balance by a large amount, so that when power is reapplied a large error voltage is created, and may drive the system very fast and damage internal components

22
Q

What scale of error is accepted in cabin altimeters?

A

± 500 ft

23
Q

How does the cabin altimeter sense cabin pressure?

A

The instrument’s case is vented directly to atmosphere

The vent is usually protected by a renewable filter

24
Q

How does a dual altimeter and differential pressure gauge display differential pressure?

A

Both atmosphere and cabin altitudes are displayed using different pointers

The difference between the two pointers is used to indicate pressure differential in psi

25
Q

What is the altitude capsule in the cabin differential pressure gauge connected to?

A

Aircraft static system

26
Q

What are the safety precautions to be taken when pressure testing the cabin with regards to the cabin altimeter and differential pressure gauge?

A

The unit is only designed to operate with less than atmospheric pressure, therefore damage to the aneroid capsules and the transmission could result

It can be temporarily removed, or the cabin vent must be blanked

27
Q

What is the term used to describe the airspeed shown on the instrument?

A

Indicated airspeed

28
Q

How does indicated airspeed become calibrated airspeed?

A

Indicated airspeed has to be corrected for instrument error and aircraft pressure error, during calibration of by the pilot

29
Q

How does calibrated airspeed become true airspeed?

A

A correct for air density is carried out using outside air temperature to obtain TAS

30
Q

What are colour arcs and radial lines known as on an ASI?

A

Range markings

31
Q

What will red radial lines signify?

A

Maximum and minimum limits of airspeed (VNE: velocity never exceed)

32
Q

What will a yellow arc signify?

A

Precautionary ranges (VNO: velocity normal operating)

33
Q

What will a green arc signify?

A

Normal operating ranges

34
Q

What will a white arc signify?

A

Ranges in which the flaps may be lowered

35
Q

How is backlash or wear in the gearing absorbed in a typical ASI?

A

Hairspring on the pointer

36
Q

What are the typical uses of an airspeed switch?

A

To switch on electrical circuits which are only needed in flight

To switch off electrical circuits which are only needed on the ground

37
Q

How is temperature compensation handled in an ASI?

A

Small strip of invar steel is laminated to the ranging bar

The bar will be straight at 15°C but will bend when the temperature changes

38
Q

How does the capsule expansion change with airspeed?

A

Small at low speeds and large at high speeds

39
Q

What is the banana slot?

A

Slot in the sector gear which is so shaped so that there is some lost motion as the scale increases

40
Q

What is square law correction?

A

Taking allowances for the uneven capsule expansion due to the fact that pressure increases four times as speed doubles, to give a nearly linear scale

41
Q

What are fitted to British made VSIs?

A

Mechanical stops to prevent pointer movement exceeding the maximum scale reading

They limit the push rod travel but allow the capsule to expand and contract beyond its normal range

42
Q

What are included in VSIs to compensate for density variations?

A

Metering unit

43
Q

What are the two types of metering units in common use in VSIs?

A
  • Ceramic type
  • Capillary and hole (orifice)
44
Q

In the capillary and hole type of metering unit in a VSI, how does air density affect the component?

A
  • A decrease in air density will increase turbulence through the capillary and therefore increase the pressure drop across it
  • An increase in air density will decrease the turbulence through the orifice and therefore decrease the pressure drop across it
45
Q

What are used instead of a tapered screw to achieve zero adjustment in some other VSIs?

A

Eccentric shaft

46
Q

At what value of percentage is the required zero adjustment of a VSI considered unserviceable?

A

More than 10% of the maximum reading

47
Q

What is a variometer?

A

Instantaneous vertical speed indicator

Piston on a spring is affected by inertia, so pumps air out or draws air in at the moment a vertical change in displacement is effected, which gives an instantaneous reading on the VSI

48
Q

What is the speed of sound at sea level and at 40,000 feet?

A

Sea level - 760 mph

40,000 feet - 650 mph

49
Q

What is the simple expression for Mach number?

A

(Pitot - Static)/Static

50
Q

What will happen to the reading of a Mach meter when altitude is increased but airspeed is maintained constant?

A

The gauge will indicate a higher Mach number

51
Q

What is the ‘Barber’s pole’ on a combined ASI and machmeter?

A

Indication of the onset of high-speed buffet due to the aircraft reaching its critical Mach number

The ‘Barber’s pole’ is linked to altitude and speed and is the setting of aircraft speed in knots which is the equivalent of the critical Mach number at the altitude the aircraft is flying at

Module 13 EASA Part 7 Book 1 (3 decks)

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