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CAA NZ IR Instruments and Navaids study materials
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CAA NZ IR Instruments and Navaids practice questions

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Question 1Flight instruments and instrument systems

In a light aircraft, which instrument is connected directly to the static pressure source and displays altitude above a selected reference pressure datum?

  1. The airspeed indicator
  2. The altimeter Correct answer.
  3. The vertical speed indicator
  4. The turn coordinator

Explanation

The altimeter is a pressure-sensitive instrument that converts static pressure into a height reading using the pressure set in its subscale window. The pilot sets the QNH, QFE or standard pressure so the instrument indicates height above the chosen datum. The other instruments use pitot pressure, rate of pressure change, or gyroscopic sensing.

Question 2Flight instruments and instrument systems

A pilot climbs with the pitot heat off in icing conditions and the pitot tube becomes blocked while the static port stays clear. What will the airspeed indicator most likely show?

  1. It will behave like an altimeter, increasing in the climb Correct answer.
  2. It will over-read steadily as altitude increases
  3. It will immediately fall to zero
  4. It will freeze at the speed at the moment of blockage

Explanation

With a blocked pitot and a clear static port, the trapped pitot pressure stays constant while static pressure falls during climb. The indicator therefore interprets a growing pressure difference and climbs like an altimeter. In a descent the reverse happens and the ASI under-reads.

Question 3Flight instruments and instrument systems

What is the primary purpose of the alternate static source in a light aircraft?

  1. To power the gyroscopic instruments from engine suction
  2. To supply static pressure to the instruments if the normal static port becomes blocked Correct answer.
  3. To allow the altimeter to be set to a different pressure datum
  4. To provide a backup pitot pressure source for the airspeed indicator

Explanation

The alternate static source lets the pilot select cabin air as the static reference when the external port is blocked, restoring instrument indications. Because cabin pressure is usually slightly lower than ambient, the ASI, altimeter and VSI may read slightly high when it is used. It has no role in pitot pressure or gyro power.

Question 4Flight instruments and instrument systems

An aircraft is flying at a constant indicated altitude with the subscale set to 1013 hPa. The actual QNH at the aircraft's position is 1003 hPa. How does the true altitude compare with the indicated altitude?

  1. The aircraft is at the indicated altitude
  2. The aircraft is lower only if temperature is above ISA
  3. The aircraft is lower than indicated Correct answer.
  4. The aircraft is higher than indicated

Explanation

When the subscale is set higher than the local QNH, the altimeter over-reads and the aircraft is lower than indicated. The rule of thumb is high to low, look out below. Flying at a fixed indicated altitude with a subscale 10 hPa too high puts the aircraft roughly 80 feet lower than shown per hPa.

Question 5Flight instruments and instrument systems

During a descent from a cold, high-altitude airfield, how does low temperature affect the true altitude of an aircraft flying at a constant indicated altitude?

  1. Temperature has no effect on true altitude
  2. The aircraft is higher only below the transition altitude
  3. The aircraft is higher than the altimeter indicates
  4. The aircraft is lower than the altimeter indicates Correct answer.

Explanation

Cold air is denser, so pressure levels are compressed toward the surface. At a given indicated altitude in cold air the aircraft is closer to the ground than the altimeter suggests. The rule of thumb is high to low, look out below, and temperature error is largest at high altitude and low temperature.

Question 6Flight instruments and instrument systems

What does the vertical speed indicator actually measure?

  1. The rate of change of static pressure Correct answer.
  2. The rate of change of pitch attitude
  3. The absolute static pressure at the aircraft
  4. The difference between pitot and static pressure

Explanation

The VSI compares the current static pressure with a delayed pressure inside a calibrated leak chamber, so it responds to the rate at which static pressure changes. This rate is displayed as climb or descent in feet per minute. It does not measure pitot pressure or attitude.

Question 7Flight instruments and instrument systems

What is indicated airspeed (IAS) corrected for position error and instrument error called?

  1. True airspeed
  2. Calibrated airspeed Correct answer.
  3. Equivalent airspeed
  4. Ground speed

Explanation

Calibrated airspeed (CAS) is IAS corrected for position (installation) error and instrument error. True airspeed additionally corrects CAS for altitude and temperature effects on density. Ground speed is the aircraft's speed over the ground, affected by wind.

Question 8Flight instruments and instrument systems

On a standard day, what is the purpose of the white arc on an airspeed indicator?

  1. It marks the flap operating speed range Correct answer.
  2. It marks the never-exceed speed
  3. It marks the maximum structural cruising speed
  4. It marks the normal operating speed range

Explanation

The white arc shows the flap operating range, from the full-flap stall speed to the maximum flap extended speed. The green arc shows the normal operating range and the yellow arc the caution range. The red radial line marks VNE.

Question 9Flight instruments and instrument systems

What does the yellow arc on an airspeed indicator represent?

  1. The range where the stall warning is active
  2. A caution range to be used only in smooth air Correct answer.
  3. The flap extension speed range
  4. The normal operating range for all flight

Explanation

The yellow arc extends from the maximum structural cruising speed to VNE and marks a caution range to be entered only in smooth air. Turbulence in this range can impose loads that exceed structural limits. The green arc is the normal operating range.

Question 10Flight instruments and instrument systems

An aircraft with a ram-air driven attitude indicator is in a steep climb. What happens to the gyro's indication as the climb continues?

  1. It progressively indicates a false climb attitude Correct answer.
  2. It fails and the gyro spins down immediately
  3. It shows a false descent attitude
  4. It remains accurate because the gyro is gravity-referenced

Explanation

A suction-driven attitude indicator relies on an air-driven gyro whose erection mechanism assumes normal flight. In sustained climbs or descents the erection system causes the horizon bar to drift toward a false climb indication. The error is greatest in prolonged climbs and is a known limitation of these instruments.

Question 11Flight instruments and instrument systems

What is the primary function of a turn coordinator?

  1. To indicate the aircraft's pitch and bank attitude
  2. To show the aircraft's heading relative to magnetic north
  3. To indicate rate of turn and whether the turn is coordinated Correct answer.
  4. To display the rate of climb and descent

Explanation

The turn coordinator shows rate of turn and, through the slip-skid indicator, whether the turn is coordinated. It is a gyroscopic instrument that senses yaw and roll, unlike the older turn-and-slip indicator which senses yaw only. It does not display attitude or heading.

Question 12Flight instruments and instrument systems

In a turn-and-slip indicator, what does the ball in the slip indicator show when it is deflected to the inside of the turn?

  1. The aircraft is skidding and the turn is not coordinated
  2. The aircraft is slipping and the turn is not coordinated Correct answer.
  3. The aircraft is in a coordinated turn
  4. The instrument has failed and should be disregarded

Explanation

The inclinometer ball responds to the resultant of gravity and centrifugal force. If the ball is to the inside of the turn, the aircraft is slipping and too little rudder is applied. If it is to the outside, the aircraft is skidding and too much rudder is applied.

Question 13Flight instruments and instrument systems

What does the heading indicator (direction gyro) rely on to maintain its reference in azimuth?

  1. The Earth's magnetic field sensed by a flux valve
  2. The static pressure at altitude
  3. The rigidity of a spinning gyro in space Correct answer.
  4. The rate of change of pitot pressure

Explanation

The heading indicator uses the rigidity of a spinning gyro to maintain a fixed reference in space. Because it is not north-seeking, it must be aligned with the magnetic compass before flight and checked periodically for precession. It does not sense the magnetic field directly.

Question 14Flight instruments and instrument systems

A magnetic compass reads 0 degrees when the aircraft is on a northerly heading and 180 degrees on a southerly heading. What is this behaviour called?

  1. Turning error Correct answer.
  2. Deviation
  3. Acceleration error
  4. Variation

Explanation

Turning error is the tendency of the magnetic compass to lag or lead during turns, and it is greatest on northerly and southerly headings. When turning through north the compass lags, and when turning through south it leads. Acceleration error is the apparent turn toward north or south during speed changes.

Question 15Flight instruments and instrument systems

When accelerating the aircraft on an east or west heading, which way does the magnetic compass appear to turn?

  1. It stays steady
  2. Toward north Correct answer.
  3. It turns toward the nearest pole
  4. Toward south

Explanation

Acceleration error makes the compass appear to turn toward north when accelerating on an east or west heading. Deceleration produces an apparent turn toward south. The effect arises because the compass card dip is unbalanced by the horizontal acceleration.

Question 16Flight instruments and instrument systems

What is the purpose of the slip indicator in a turn coordinator?

  1. To show whether the aircraft is coordinated in yaw Correct answer.
  2. To show the aircraft's bank angle
  3. To show the rate of turn in degrees per second
  4. To display the aircraft's angle of attack

Explanation

The slip indicator, or inclinometer, shows whether the aircraft is coordinated in yaw by displaying the lateral acceleration on the ball. The rate of turn is shown by the miniature aircraft symbol. Bank angle and angle of attack are shown by other instruments.

Question 17Flight instruments and instrument systems

Which instrument would be affected if an aircraft's static port were completely blocked while the pitot tube remained clear?

  1. Only the airspeed indicator
  2. The altimeter, vertical speed indicator and airspeed indicator Correct answer.
  3. Only the vertical speed indicator
  4. Only the altimeter

Explanation

All three pitot-static instruments use static pressure, so a blocked static port affects all of them. The altimeter freezes at the altitude at which the blockage occurred, the VSI reads zero, and the ASI behaves like an altimeter. Pitot pressure remains available but is not enough to give correct readings.

Question 18Flight instruments and instrument systems

What is indicated by a red radial line on an airspeed indicator?

  1. The maximum flap extended speed
  2. The maximum structural cruising speed
  3. The stall speed in the landing configuration
  4. The never-exceed speed Correct answer.

Explanation

The red radial line marks the never-exceed speed (VNE), the maximum speed at which the aircraft may be operated. The top of the green arc is the maximum structural cruising speed, and the top of the white arc is the maximum flap extended speed. The bottom of the white arc is the full-flap stall speed.

Question 19Flight instruments and instrument systems

What is the approximate true altitude error per 1 hPa of pressure error at low altitude?

  1. About 80 feet
  2. About 1000 feet
  3. About 30 feet Correct answer.
  4. About 300 feet

Explanation

Near sea level, 1 hPa of pressure error corresponds to about 30 feet of altitude error. This is why setting the correct QNH is important, and why a 10 hPa error gives roughly 300 feet of error. The figure increases with altitude as pressure levels are further apart.

Question 20Flight instruments and instrument systems

Which of the following best describes the behaviour of the vertical speed indicator immediately after a rapid, sustained change in pitch?

  1. It reads in the opposite direction to the actual trend
  2. It shows the trend immediately but settles to a steady reading after a short lag Correct answer.
  3. It is unaffected by pitch changes
  4. It shows a steady reading instantly with no lag

Explanation

The VSI responds quickly to a change in static pressure and shows the trend, but the calibrated leak takes a few seconds to stabilise, so the steady reading lags slightly. This is why the VSI is described as a trend instrument. It does not reverse the trend or ignore pitch changes.

Question 21Flight instruments and instrument systems

An attitude indicator has a caging knob. What is its purpose?

  1. To test the stall warning system
  2. To select the alternate static source
  3. To lock the gyro and erect it to the correct attitude before flight Correct answer.
  4. To adjust the altimeter subscale

Explanation

The caging knob locks the gyro and forces the horizon bar to a known attitude, allowing the instrument to be erected and checked before flight. Once erected, the gyro maintains its reference in space. It has no connection with the altimeter, static system or stall warning.

Question 22Flight instruments and instrument systems

What is the main advantage of an electrically driven attitude indicator over a suction-driven one?

  1. It does not need any power source
  2. It is less susceptible to errors caused by the erection system in sustained climbs Correct answer.
  3. It eliminates the need for a turn coordinator
  4. It provides a direct magnetic heading reference

Explanation

Electrically driven attitude indicators generally have more sophisticated erection mechanisms and are less prone to the false climb indication that affects suction-driven instruments in prolonged climbs. They still require electrical power and do not provide magnetic heading. The turn coordinator remains a separate instrument.

Question 23Flight instruments and instrument systems

What is the function of a pitot tube heater?

  1. To warm the gyro bearings
  2. To heat the cabin for the pilot
  3. To increase pitot pressure at altitude
  4. To prevent ice from blocking the pitot tube and static ports Correct answer.

Explanation

Pitot heat prevents ice from forming in the pitot tube and, on some installations, the static ports, which would cause erroneous airspeed and altitude indications. It is used in visible moisture near or below freezing. It does not heat the cabin or affect gyro operation.

Question 24Flight instruments and instrument systems

An aircraft is climbing at a constant indicated airspeed. How does true airspeed compare with indicated airspeed as altitude increases?

  1. True airspeed is higher than indicated airspeed Correct answer.
  2. True airspeed is higher only in a descent
  3. True airspeed is lower than indicated airspeed
  4. True airspeed equals indicated airspeed

Explanation

As altitude increases, air density falls, so the same dynamic pressure corresponds to a higher true airspeed. True airspeed is therefore higher than indicated airspeed at altitude, roughly 2 percent per 1000 feet. The reverse applies in a descent, but the question concerns a climb.

Question 25Flight instruments and instrument systems

What is the purpose of the compass deviation card?

  1. To record the local magnetic variation
  2. To record the error caused by the aircraft's own magnetic fields on each heading Correct answer.
  3. To show the aircraft's weight and balance limits
  4. To list the altimeter pressure settings for each airfield

Explanation

The deviation card records the difference between the compass reading and magnetic heading caused by magnetic fields within the aircraft. It is used to convert between compass heading and magnetic heading. Variation is a separate angular difference between true and magnetic north.

Question 26Flight instruments and instrument systems

On a standard pressure altimeter, what does the subscale setting (Kollsman window) actually do when you rotate the knob?

  1. It moves the pointer assembly relative to a fixed pressure-reference scale Correct answer.
  2. It changes the internal gear ratio so the pointer responds faster
  3. It adjusts the diaphragm capsule's aneroid reference pressure
  4. It compensates the instrument for non-standard temperature

Explanation

Rotating the subscale knob moves the mechanical linkage and pointer assembly so the indicated altitude corresponds to a different reference pressure, while the capsule continues to sense static pressure unchanged. The capsule's internal reference is sealed and cannot be adjusted in flight.

Question 27Flight instruments and instrument systems

An aircraft on the ground at an aerodrome with elevation 1500 ft has its altimeter subscale set to the aerodrome QNH. What should the altimeter read?

  1. Pressure altitude for that aerodrome
  2. 1500 ft plus the standard temperature correction
  3. Zero feet
  4. Aerodrome elevation, approximately 1500 ft Correct answer.

Explanation

QNH is the pressure setting that causes the altimeter to indicate aerodrome elevation when the aircraft is on the ground at that aerodrome. This is the basis of the QNH/QFE convention used in New Zealand altimetry.

Question 28Flight instruments and instrument systems

In a light aircraft with a conventional pitot-static system, which instruments are connected to the static source?

  1. Altimeter, vertical speed indicator and airspeed indicator Correct answer.
  2. Airspeed indicator only
  3. Altimeter and vertical speed indicator only
  4. Airspeed indicator and altimeter only

Explanation

The static source supplies the altimeter, the vertical speed indicator and the static (case) side of the airspeed indicator. Only the pitot (dynamic) pressure is fed solely to the airspeed indicator.

Question 29Flight instruments and instrument systems

What does the green arc on a typical light aircraft airspeed indicator represent?

  1. The normal operating speed range in the clean configuration Correct answer.
  2. The speed range in which the aircraft may be operated indefinitely
  3. The normal operating speed range with flaps extended
  4. The maximum speed for turbulent air penetration

Explanation

The green arc marks the normal operating range from the clean stall speed (lower limit) up to the maximum structural cruising speed Vno. Flap limiting speed is shown separately, usually as a white arc.

Question 30Flight instruments and instrument systems

Which property of a gyroscope makes the heading indicator maintain a stable indication in azimuth?

  1. The pendulous vanes that erect the gyro
  2. Precession caused by the Earth's rotation
  3. Rigidity in space of a spinning rotor Correct answer.
  4. Sensitivity of the rotor to magnetic variation

Explanation

The heading indicator uses the rigidity in space of a rapidly spinning rotor so that its spin axis remains fixed relative to inertial space. Because the aircraft turns around it, the card shows changes in heading.

Question 31Flight instruments and instrument systems

What is the purpose of the caging or fast-erection mechanism on a slaved heading indicator?

  1. To rapidly align the gyro indication with the sensed magnetic heading after start-up Correct answer.
  2. To prevent the gyro from precessing during turns
  3. To lock the gyro during aerobatics only
  4. To remove the need for a magnetic slaving accessory

Explanation

The caging or fast-erection control is used after start-up to bring the gyro heading rapidly into agreement with the flux valve sensed magnetic heading. Once aligned, the slaving system maintains synchronisation during normal flight.

Question 32Flight instruments and instrument systems

What does a turn coordinator's miniature aircraft indicate?

  1. Angle of bank directly in degrees
  2. Rate of yaw only
  3. Rate of pitch change
  4. Rate of roll and yaw combined, giving rate of turn Correct answer.

Explanation

The turn coordinator's gyro is canted so the miniature aircraft responds to both roll and yaw, indicating the rate at which the aircraft is turning. It is calibrated so a standard rate turn is shown at a defined mark.

Question 33Flight instruments and instrument systems

What causes the magnetic compass to indicate a turn toward the north when the aircraft is accelerating on a northerly heading?

  1. The compass card's inertia causing it to swing
  2. Magnetic dip acting on the compass card Correct answer.
  3. Deviation from aircraft electrical equipment
  4. Variation between true and magnetic north

Explanation

On a northerly heading the compass magnet aligns with the horizontal component of the Earth's field, which is weaker than the total field. Acceleration tilts the resultant field and the compass senses a turn toward north, an effect caused by magnetic dip.

Question 34Flight instruments and instrument systems

An aircraft with a standard pressure altimeter flies from a region of high pressure into a region of low pressure without changing the subscale setting. How does the true altitude compare with the indicated altitude?

  1. True altitude is higher than indicated
  2. True altitude is lower than indicated Correct answer.
  3. True altitude equals indicated altitude
  4. True altitude is higher only if temperature is above standard

Explanation

When flying from high to low pressure at a constant indicated altitude, the aircraft is actually descending relative to the pressure surfaces, so true altitude is lower than indicated. This is the basis of the rule to reset the altimeter when pressure changes significantly.

Question 35Flight instruments and instrument systems

During a constant-rate climb at a fixed vertical speed, what does the VSI show immediately after the climb is established and then a short time later?

  1. A reading that oscillates continuously
  2. A steady reading throughout the climb
  3. A steady under-read throughout the climb
  4. A momentary over-read, then settling to the actual rate Correct answer.

Explanation

The VSI has a calibrated leak that equalises case pressure slowly, so a sudden change in climb rate produces an initial lag or over-read before the indication settles. In a steady climb at constant rate the indication eventually stabilises.

Question 36Flight instruments and instrument systems

Which statement correctly describes the difference between indicated airspeed and calibrated airspeed?

  1. Calibrated airspeed equals indicated airspeed corrected for wind
  2. Calibrated airspeed equals indicated airspeed corrected for position error and instrument error Correct answer.
  3. Calibrated airspeed equals indicated airspeed corrected for compressibility only
  4. Calibrated airspeed equals indicated airspeed corrected for density altitude

Explanation

Calibrated airspeed (CAS) is indicated airspeed corrected for the installation's position error and the instrument's own error. It is the speed used when referencing most aircraft performance data.

Question 37Flight instruments and instrument systems

An aircraft's pitot tube becomes blocked by ice during a climb while the static source remains clear. What happens to the airspeed indication?

  1. It decreases steadily as altitude increases Correct answer.
  2. It remains constant at the value when the blockage occurred
  3. It increases steadily as altitude increases
  4. It drops to zero immediately

Explanation

With the pitot tube blocked, the trapped pitot pressure stays constant, but the static pressure falls as the aircraft climbs, so the differential pressure decreases and the ASI under-reads. The indication behaves like an altimeter, decreasing in a climb.

Question 38Flight instruments and instrument systems

Which error affects a direct-reading magnetic compass in a turn and causes it to lead or lag the actual heading?

  1. Turning error Correct answer.
  2. Acceleration error
  3. Deviation
  4. Variation

Explanation

Turning error occurs because the compass card is affected by magnetic dip, causing the compass to lead or lag the turn, particularly on northerly and southerly headings. It is most pronounced when turning through north or south.

Question 39Flight instruments and instrument systems

In a turn-and-slip indicator, the gyro spin axis is oriented such that the instrument primarily senses which rate?

  1. Rate of yaw Correct answer.
  2. Rate of pitch
  3. Rate of climb
  4. Rate of roll

Explanation

The turn-and-slip indicator uses a gyro whose spin axis is horizontal, so it senses yaw rate and indicates the rate of turn. The turn coordinator differs in that its gyro is canted to sense roll and yaw together.

Question 40Flight instruments and instrument systems

A pilot notices that the suction-driven attitude indicator is tumbling in a prolonged steep turn. What is the most likely cause?

  1. A blocked static port
  2. Insufficient vacuum pressure to keep the rotor at speed Correct answer.
  3. Excessive g-loading exceeding the gyro's erection limits
  4. A failed turn coordinator

Explanation

Suction-driven attitude gyros need adequate vacuum to maintain rotor speed and erection. If vacuum pressure is low, the gyro can precess or tumble during manoeuvres and give unreliable indications.

Question 41Flight instruments and instrument systems

What is the purpose of the flux valve in a slaved heading indicator system?

  1. To indicate rate of turn
  2. To sense the Earth's magnetic field and provide a reference heading Correct answer.
  3. To supply electrical power to the gyro motor
  4. To provide static pressure for erection

Explanation

The flux valve (or flux gate) senses the horizontal component of the Earth's magnetic field and provides a heading reference signal to the slaving circuit. The system then torques the gyro into alignment, keeping the heading indicator synchronised.

Question 42Flight instruments and instrument systems

An aircraft is descending at 500 ft/min and the pilot wishes to know the approximate true altitude change per minute if the temperature is significantly colder than standard. What is the general effect of cold temperature on the altimeter?

  1. The altimeter under-reads, so the aircraft is higher than indicated
  2. The altimeter over-reads, so the aircraft is lower than indicated Correct answer.
  3. The altimeter over-reads only above 10,000 ft
  4. Cold temperature has no effect on the altimeter

Explanation

In air colder than ISA, the pressure levels are compressed toward the surface, so the altimeter indicates an altitude higher than the true altitude. The aircraft is therefore lower than the altimeter suggests, which is a significant terrain-clearance hazard in cold conditions.

Question 43Flight instruments and instrument systems

What is the function of the pitot-static system's drain valve?

  1. To release excess pitot pressure during a climb
  2. To provide an alternate static source
  3. To allow trapped moisture to be removed from the pitot and static lines Correct answer.
  4. To calibrate the airspeed indicator

Explanation

Drain valves allow any accumulated moisture or contamination in the pitot and static lines to be removed during pre-flight checks. This helps prevent blockage and erroneous instrument indications.

Question 44Flight instruments and instrument systems

A pilot is flying at a constant indicated airspeed and constant altitude while the outside air temperature rises. How does the true airspeed change?

  1. True airspeed decreases
  2. True airspeed remains the same
  3. True airspeed decreases only if altitude also increases
  4. True airspeed increases Correct answer.

Explanation

True airspeed depends on air density, and warmer air is less dense. At a constant indicated airspeed the aircraft is moving through less dense air, so the true airspeed is higher.

Question 45Flight instruments and instrument systems

What is the purpose of the white arc on an airspeed indicator?

  1. To show the never-exceed speed
  2. To show the speed for best rate of climb
  3. To show the normal clean operating range
  4. To show the flap operating speed range from full flap stall to maximum flap extended speed Correct answer.

Explanation

The white arc indicates the range in which flight with flaps extended is permitted, from the full-flap stall speed up to the maximum flap extended speed Vfe. It is a limitation marking, not a performance target.

Question 46Flight instruments and instrument systems

An aircraft's static port is partially blocked by ice, causing the static pressure to lag behind actual pressure changes. Which combination of indications would most likely be observed during a climb?

  1. Altimeter under-reads, VSI shows a climb, ASI over-reads Correct answer.
  2. Altimeter over-reads, VSI shows a descent, ASI over-reads
  3. Altimeter under-reads, VSI shows a descent, ASI under-reads
  4. Altimeter over-reads, VSI shows a climb, ASI under-reads

Explanation

If static pressure lags during a climb, the trapped static pressure remains higher than ambient. The altimeter therefore under-reads, the VSI interprets the lag as a climb, and the ASI, sensing a smaller pressure differential, over-reads.

Question 47Flight instruments and instrument systems

Which statement best explains why a turn coordinator is preferred over a turn-and-slip indicator as a standby instrument in some aircraft?

  1. It operates without electrical power
  2. It provides a direct heading reference
  3. It indicates rate of turn in both roll and yaw, giving earlier warning of bank changes Correct answer.
  4. It is unaffected by gyroscopic precession

Explanation

The turn coordinator's canted gyro responds to roll as well as yaw, so it shows the aircraft beginning to bank before the turn is fully established. This makes it useful as a standby instrument for detecting bank and turn rate.

Question 48Flight instruments and instrument systems

An aircraft with a pressure altimeter set to QNH 1013 hPa flies at 5000 ft indicated toward a region where the QNH is 1005 hPa. If the subscale is not reset, what is the approximate true altitude error?

  1. Approximately 240 ft too high
  2. Approximately 240 ft too low
  3. Approximately 60 ft too high Correct answer.
  4. Approximately 60 ft too low

Explanation

Flying from higher pressure toward lower pressure without resetting the subscale causes the altimeter to over-read, so the aircraft is lower than indicated. The error is roughly 30 ft per hPa, so an 8 hPa change gives about 240 ft, and the direction is that true altitude is lower than indicated.

Question 49Flight instruments and instrument systems

A pilot observes that the heading indicator drifts slowly during a long flight and must be reset periodically against the magnetic compass. What is the most likely explanation?

  1. The turn coordinator is influencing the heading indicator
  2. The heading indicator is not affected by Earth-rate precession
  3. The magnetic compass is more accurate than the heading indicator in all conditions
  4. The gyro suffers from apparent drift and real drift, which the slaving system may not fully correct Correct answer.

Explanation

A heading indicator is subject to apparent drift from Earth-rate precession and transport wander, and real drift from bearing friction and imbalance. In an unslaved instrument these accumulate and require periodic resetting against the compass.

Question 50Flight instruments and instrument systems

An aircraft is fitted with a Machmeter and a conventional pressure altimeter. While climbing at a constant calibrated airspeed, the pilot notices the Mach number rising even though the airspeed indicator reading stays steady. Which statement best explains this behaviour?

  1. Mach number depends on the ratio of true airspeed to local speed of sound, so as altitude increases and temperature falls, the same CAS corresponds to a higher TAS and a lower speed of sound. Correct answer.
  2. The airspeed indicator is under-reading because of compressibility error, while the Machmeter shows the correct dynamic pressure.
  3. Mach number is derived directly from impact pressure alone, so any constant CAS must give a constant Mach number regardless of altitude.
  4. The Machmeter senses static pressure only, so its indication rises whenever the aircraft climbs into lower static pressure.

Explanation

Mach number is TAS divided by the local speed of sound. At constant CAS, TAS rises with altitude while the speed of sound falls with temperature, so the ratio increases and the Mach indication climbs. This is why high-altitude aircraft have both a VMO and an MMO limit, and why Mach buffet can occur at a steady IAS.