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SESK: Stuff Everyone Should Know · sesk.info/pilot-vacuum-failure-gyros

When vacuum pressure drops below normal, which instruments may become unreliable?

The attitude and heading indicators, which are vacuum-driven gyros.

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  1. The attitude and heading indicators ✔
  2. The airspeed indicator and altimeter
  3. The magnetic compass and clock

Why: In a typical small airplane, the engine-driven vacuum pump spins the attitude and heading indicator gyros. Low suction lets those gyros slow down and give unreliable readings, so watch the suction gauge.

Huh, didn't know that: In many airplanes the turn coordinator runs on electricity, so it still works when the vacuum system fails.

The dad joke
My vacuum pump quit. Now my attitude indicator has a bad attitude.
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References

Answer: The attitude and heading indicators. In a typical small airplane, the engine-driven vacuum pump spins the attitude and heading indicator gyros. Low suction lets those gyros slow down and give unreliable readings, so watch the suction gauge.

  1. Pilot's Handbook of Aeronautical Knowledge FAA-H-8083-25C, Chapter 8 www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/phak/10_phak_ch8.pdf
    the attitude and heading indicators may not provide reliable information when suction pressure is low.
    Checked 2026-10-09.

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