Aircraft Instrumentation Questions and Answers

Answer: A

Correct answer: Total pressure

The pitot tube faces into the airflow, so the air is brought to rest at its mouth and the pressure sensed is the sum of the static and the dynamic components - total, or stagnation, pressure. Dynamic pressure is never measured directly by any probe: it is obtained by subtracting the static pressure, sensed separately at a flush port, from this total.

Answer: B

A flush port senses the ambient pressure without any ram contribution, provided the local flow is clean. Position error arises precisely because no location on a real airframe is perfectly undisturbed across the whole speed and attitude range.

Answer: C

A sealed capsule expands as static pressure falls, and the movement is scaled through the standard atmosphere relationship to read height. It measures pressure and nothing else, which is why every altimeter error traces back to a pressure error.

Answer: D

Setting the local QNH makes the altimeter read elevation above sea level, so it shows the aerodrome elevation on the ground. QFE reads zero on the aerodrome and QNE is the standard 1013.25 setting used above the transition altitude.

Answer: A

Above the transition altitude every aircraft sets the same standard datum, so their indications are mutually consistent even if none is a true height. Flight levels are separations in that common reference rather than heights above the ground.

Answer: B

The capsule is fed pitot pressure and the case is fed static, so the deflection responds to dynamic pressure. Because dynamic pressure depends on density, the reading is not true airspeed except at sea level in the standard atmosphere.

Answer: C

The chain runs indicated, then calibrated after position and instrument error, then equivalent after compressibility, then true after density. Each correction addresses one distinct physical effect and they are applied in that order.

Answer: D

At low speed and low altitude the correction is negligible, which is why it is often ignored in light aircraft work. It grows quickly above about 200 knots and at altitude, where the air can no longer be treated as incompressible.

Answer: A

Correct answer: Air density

The chain runs indicated, calibrated, equivalent, true, and each step removes one effect. Instrument and position error take indicated to calibrated, compressibility takes calibrated to equivalent, and density takes equivalent to true. Wind belongs to none of them - it converts true airspeed to ground speed, which is a navigation quantity rather than an air data one.

Answer: B

A capsule connected to the static line is surrounded by a case that bleeds towards the same pressure through a restriction, so the pressure difference is proportional to rate of change. The restriction is also the source of the instrument's characteristic lag.