Air Data Instruments Questions and Answers

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Separate mechanical instruments each have their own calibration and their own errors, so they can disagree with one another. An air data computer takes one set of pressure and temperature inputs and derives altitude, airspeed, Mach number and vertical speed from them consistently, so the displayed values agree by construction.

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 describe the two pressure sources correctly. Statement 3 is the common misconception: no probe senses dynamic pressure directly. The airspeed indicator senses total pressure on one side of a capsule and static on the other, and the deflection responds to their difference, which is the dynamic pressure - obtained by subtraction, not by measurement.

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 give the first two links of the chain correctly. Statement 3 is wrong: true airspeed comes from equivalent airspeed by correcting for density, not for wind. Applying a wind correction to true airspeed gives ground speed, which is a navigation quantity and lies outside the air data chain entirely.

Answer: D

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: QNH references mean sea level so the altimeter reads elevation on the ground, and QFE references aerodrome level so it reads zero there. Statement 3 is wrong - the standard setting of 1013.25 gives pressure altitude, which equals true altitude only when the atmosphere happens to be standard. Its purpose is a common reference, not accuracy.

Answer: A

The first two are correct. With both openings blocked the trapped total pressure makes the indication rise as the aircraft climbs, which is the classic icing signature and the opposite of what the third statement claims.

Answer: B

Correct answer: A-1, B-2, C-3, D-4

Four instruments and four distinct uses of the same two pressures. The altimeter needs static alone. The airspeed indicator needs their difference. The vertical speed indicator needs the rate at which static is changing. And the machmeter needs their ratio, which is what makes it independent of temperature and density.

Answer: C

Correct answer: A-1, B-2, C-3, D-4

The chain is cumulative, each speed being the previous one with one more correction applied. Indicated is what the dial shows; calibrated removes instrument and position error; equivalent removes the compressibility effect; and true removes the density difference from sea level standard. Miss a step and the errors compound, which at altitude can amount to a hundred knots or more.

Answer: D

Correct answer: A-1, B-2, C-3, D-4

Each failure has its own signature. A blocked static traps the reference pressure, so airspeed reads low in a climb and high in a descent. A blocked pitot with a clear drain lets the total pressure bleed away and the reading falls towards zero. With the drain blocked too the total is sealed and the reading rises in a climb. A static leak into an unpressurised cabin feeds a slightly low pressure, so the reading is a little high throughout.

Answer: A

Correct answer: A-1, B-2, C-3, D-4

Four references, three barometric and one not. QNH is set so the altimeter reads height above mean sea level, QFE so it reads zero on the aerodrome, and QNE is the standard 1013.25 datum used above the transition altitude. The radio altimeter is not barometric at all: it measures the actual distance to the terrain directly beneath the aircraft.

Answer: B

Correct answer: Height above the terrain below

The pitot-static system senses pressure, and pressure tells you nothing about what lies underneath the aircraft. Height above terrain comes from a radio altimeter, which times a signal reflected from the ground. The other three - vertical speed, pressure altitude and indicated airspeed - are all derived from the static and total pressures.