FAA Instrument Rating Airplane (IRA)Flight Instruments and SystemsMedium
During flight in severe icing conditions, both the ram air inlet and the drain hole of the pitot tube become completely blocked, while the static ports remain clear and unobstructed. How will the airspeed indicator most likely behave during a subsequent climb?
- AAirspeed will increase progressively, behaving like an altimeter
- BAirspeed will remain frozen at the value present when the blockage occurred
- CAirspeed will immediately drop to zero
- DAirspeed will decrease progressively, behaving like an inverted altimeter
Show answer & explanationAnswer & explanation
Correct answer: A. Airspeed will increase progressively, behaving like an altimeter
With both pitot openings blocked, the pressure trapped in the pitot line remains essentially constant while the static pressure decreases with altitude; since airspeed is measured by pitot pressure minus static pressure, the differential increases during a climb, causing the airspeed indicator to falsely increase like an altimeter.
Why the other options are wrong
- B. A frozen airspeed would only occur if static pressure were also trapped, not with static ports clear.
- C. Zero airspeed would result from a total blockage with no differential pressure change, which doesn't match this scenario.
- D. This describes the opposite trend; the differential increases, not decreases, during a climb.
Total Pitot Blockage (Ram + Drain)
When both the pitot ram air inlet and drain hole are blocked but static ports remain open, trapped pitot pressure stays constant, causing the airspeed indicator to act like an altimeter (increasing in climbs, decreasing in descents).
- Differs from partial blockage (drain open), which causes ASI to act like altimeter in reverse pattern
- Static pressure continues functioning normally
- Cross-check with altimeter and VSI trends to identify this failure
Memory trick: Trapped air plus falling outside pressure equals a rising 'fake' airspeed.