Air Data Instruments Questions and Answers

Answer: C

Correct answer: Only three

Three of the four are correct. The fourth is not: with the static port blocked the trapped pressure stops changing, so the vertical speed indicator reads zero, not a steady climb. That zero reading in a genuine climb is itself the diagnostic clue, and it should be cross-checked against the attitude indicator and the power setting.

Answer: D

Correct answer: Only three

The first three definitions are right. Equivalent airspeed is the one that is wrong: it is calibrated airspeed corrected for compressibility, still an air-relative quantity. Speed relative to the ground is ground speed, which lies outside the airspeed correction chain altogether because it depends on the wind rather than on any property of the air the aircraft is flying through.

Answer: A

Correct answer: Radio altitude

A radio altimeter transmits a signal downward and times its return, so it measures the distance to whatever lies beneath the aircraft - terrain, water or a building. It has no connection to the pitot-static system. The other three are all derived from pressure: static alone for pressure altitude, total minus static for airspeed, and the rate of change of static for vertical speed.

Answer: B

Correct answer: Ground speed

The correction chain runs indicated to calibrated to equivalent to true, each step removing one effect of the instrument or of the air. Ground speed lies outside it: it is true airspeed combined with the wind vector, and it is a navigation quantity. No amount of air data correction will produce it, and no wind correction belongs anywhere in the chain.

Answer: C

Correct answer: Airspeed reads zero

A falling airspeed towards zero is the signature of a blocked pitot with a clear drain, which lets the trapped total pressure bleed away until it equals static. A blocked static port leaves the total line intact, so the difference across the capsule never vanishes. Its actual effects are the other three: a frozen altimeter, a zero vertical speed, and an airspeed reading low in a climb and high in a descent.

Answer: D

The other three set the pressure datum the instrument references, giving height above the field, above sea level or on the standard datum. QDM is the magnetic bearing to a station and belongs to radio navigation entirely.

Answer: A

Correct answer: Wind velocity

Wind moves the whole air mass and the aircraft with it, so it changes ground speed while leaving every air-relative quantity untouched. The gap between indicated and true airspeed comes from density, from compressibility at higher Mach numbers, and from position error. An aircraft in a 100 knot headwind indicates exactly what it would in still air.

Answer: B

Trapped total pressure makes the differential grow as static pressure falls in the climb, so the instrument tracks height rather than speed. That the altimeter and vertical speed indicator are normal confirms the static side is healthy.

Answer: C

All three symptoms share one cause: a static line trapped at some pressure. The altimeter has nothing to respond to, the vertical speed indicator sees no rate, and the airspeed differential grows as the aircraft descends into denser air.

Answer: D

Correct answer: As the expected effect of venting to slightly reduced cabin pressure

In an unpressurised aircraft the cabin runs slightly below ambient because of the flow over and through the airframe. Venting the static line to the cabin therefore feeds the instruments a lower pressure, which the altimeter reads as extra height and the airspeed indicator as extra speed. The shift is small and predictable, and the correction is published in the flight manual.