Air Data Instruments Questions and Answers

Answer: C

Correct answer: The ratio of true airspeed to the local speed of sound

Mach number is by definition the ratio of the aircraft’s speed to the speed of sound in the air it is flying through. Both quantities change with altitude and temperature, which is why Mach rather than airspeed governs compressibility effects - an aircraft can reach a critical Mach number at a true airspeed that would be quite unremarkable near sea level.

Answer: D

With the ram inlet blocked and the drain open, the pitot line vents to static pressure and the differential collapses. If instead both the inlet and the drain are blocked, the trapped pressure makes the instrument behave like an altimeter.

Answer: A

The trapped total pressure stays constant while static pressure falls with altitude, so the differential grows as the aircraft climbs. The instrument then behaves as a crude altimeter, which is the classic icing signature.

Answer: B

With the static line sealed the capsule sees a constant pressure and the needle stops responding. The airspeed indicator meanwhile reads low in a climb and high in a descent, and the vertical speed indicator sits at zero.

Answer: C

Cabin pressure is slightly below ambient because of flow over the fuselage, so the altimeter typically reads slightly high and the airspeed slightly high when it is selected. The flight manual tabulates the correction for exactly that reason.

Answer: D

Flow accelerating over the fuselage changes the local pressure, and the difference varies with angle of attack and Mach number. It is the reason a calibration card exists and why the error is largest at low speed and high angle of attack.

Answer: A

Adiabatic compression at the probe raises the sensed temperature above the ambient value, and the rise grows with the square of Mach number. The air data computer subtracts it to recover the static temperature that true airspeed calculations need.

Answer: B

Because stall occurs at an angle of attack rather than at a speed, the vane gives a warning valid at any weight or load factor. That is the argument for stall protection based on it rather than on indicated airspeed alone.

Answer: C

It takes total pressure, static pressure and total air temperature and computes altitude, airspeed, Mach number, vertical speed and static temperature. Feeding one digital source to every display removes the discrepancies separate mechanical instruments used to show.

Answer: D

Ice accretion at the inlet is the classic cause of a trapped-pressure airspeed failure. Because the failure develops silently and mimics a genuine speed change, heater use is a checklist item before entering visible moisture.