Friday, October 23, 2026 · Captain's Challenge
The Captain's Challenge.
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Climbing in icing with the pitot heat inoperative, ice blocks both the pitot tube's ram-air inlet and its drain hole. The static ports stay clear. How will the airspeed indicator behave as the climb continues?
The answer
4It will over-read more and more, like an altimeter
Explanation
With the ram-air inlet and the drain hole both blocked, the air trapped in the pitot line keeps its pressure while static pressure falls with height, so the difference the indicator measures grows: indicated airspeed rises in a climb and falls in a descent, and the airspeed indicator behaves like an altimeter (From the Ground Up, Flight Instruments, pitot-static system). If only the ram inlet ices and the drain stays open, the trapped pressure bleeds off and the reading falls toward zero. TC AIM AIR 2.7.1 warns that icing "can be rapid and may result in almost instantaneous power failure or airspeed indication loss", and CARs 705.82 bars take-off in a transport category aeroplane equipped with flight instrument pitot heating unless it also has a pitot heat indication system meeting AWM 525.1326.
Memory tip: Pitot and drain blocked = the ASI becomes an altimeter: fast in the climb, slow in the descent. Ram inlet only = falls to zero.
Source
From the Ground Up, Flight Instruments (pitot-static system); TC AIM AIR 2.7.1; CARs 705.82
Taught in: IATRA › Instruments and Avionics SystemsThis question is from the IATRA course, which teaches every IATRA subject and drills it like this. Unlock all 6 chapters with their quizzes (90 questions), and 6 full-length IATRA mock exams.
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