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Whilst flying in straight and level flight, if the pitot tube becomes blocked, what will happen to your airspeed indicator (ASI)?

  • A

    It will under-read your actual speed slightly.

  • B

    It will over-read your actual speed.

  • C

    It will freeze at the current indicated airspeed.

  • D

    It will read its maximum displayable value.

Refer to figures.
PITOT BLOCKAGE

The airspeed indicator is the only instrument affected by a pitot tube blockage.
If the pitot system becomes completely clogged and the static system remains clear, the indicator reacts as an altimeter, showing an increase in airspeed when climbing and a decrease in speed when descending. As the descent is made, the static pressure would increase against the diaphragm causing it to compress, thereby resulting in an indication of decreased airspeed. The opposite would happen in a climb.

Therefore, as there are no changes to the altitude in straight and level flight, the pitot blockage would just cause the airspeed indicator to freeze in exactly the position it was in when the blockage occurred. This is because no changes are occurring to either total (pitot) pressure or static pressure in that scenario.

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