Air Data Instruments Questions and Answers

Answer: C

Correct answer: False, it reads true airspeed only at sea level standard density

The instrument responds to dynamic pressure and is graduated on the assumption of sea level standard density. Where the actual density is lower the same speed produces less dynamic pressure, so the reading falls below the true airspeed and the gap widens with altitude. The instrument is not density compensated; correcting for density is the pilot’s or the air data computer’s task.

Answer: D

Correct answer: The vertical speed indicator shows a steady climb

This is the false statement. With the static port blocked the trapped pressure stops changing, so the vertical speed indicator reads zero regardless of what the aircraft is doing. The other three are all genuine consequences: the altimeter freezes at the blockage altitude, and the airspeed reads low in a climb and high in a descent because the reference pressure no longer follows the ambient.

Answer: A

Cold air is denser, so a given pressure occurs at a lower height than the standard atmosphere assumes. True altitude is therefore below the indication, in the same direction as the error from flying towards lower pressure.

Answer: B

Correct answer: A change in wind velocity

Wind carries the entire air mass, so an aircraft flying in it experiences exactly the same relative flow as one in still air - every air data quantity is unchanged, and only the ground speed differs. Density, altitude and temperature all alter the relation between the two airspeeds, because all three change the air density the instrument was calibrated against.

Answer: C

Correct answer: No, the temperature terms cancel in the pressure ratio

Mach number is a function of the ratio of total to static pressure alone. Both temperature and density appear in the underlying expressions but cancel when the ratio is formed, so the machmeter needs no temperature probe. The distractor about the speed of sound depending on temperature is true in itself but does not apply, because the machmeter never computes the speed of sound explicitly.

Answer: D

The alternate source restores a working static line, so the vertical speed indicator responds normally. A steady zero indicates the static line is still blocked, which is the condition the selection was meant to relieve.

Answer: A

Correct answer: False, stalling speed rises with weight while stalling angle stays fixed

A wing stalls when it reaches its stalling angle of attack, and that angle is essentially a property of the aerofoil. The speed at which it is reached depends on how much lift is required, so it rises with the square root of weight and of load factor. This is precisely why angle of attack is the better basis for stall protection than airspeed.

Answer: B

Correct answer: Ground speed

The chain is indicated, calibrated, equivalent, true, and each step removes one air data effect. Ground speed is not part of it: it is what you get by adding the wind vector to true airspeed, and it belongs to navigation rather than to air data. Treating it as the last link of the chain is a common and consequential confusion.

Answer: C

Venting through the drain collapses the differential across the capsule. The rising indication belongs to the case where the drain is blocked as well, which traps the total pressure and turns the instrument into a crude altimeter.

Answer: D

Correct answer: Selecting the alternate static source

The alternate static source addresses a blocked static port, not a blocked pitot. If the pitot has iced over, switching the static source changes nothing about the total pressure line where the fault lies. The other three all bear on the pitot: heat applied before entering icing conditions, a checklist that ensures it is applied, and a cross-check of airspeed against attitude and power that catches the failure early.