FAA Instrument Rating Airplane (IRA)Flight Instruments and SystemsMedium
An aircraft's vacuum pump fails in flight. Which flight instrument will continue to operate normally and should be used as the primary bank reference during partial-panel operations?
- ATurn coordinator
- BAttitude indicator
- CHeading indicator
- DVertical speed indicator
Show answer & explanationAnswer & explanation
Correct answer: A. Turn coordinator
In most light aircraft, the attitude indicator and heading indicator are vacuum-driven, while the turn coordinator is electrically powered. After a vacuum pump failure, the turn coordinator remains functional and becomes the primary reference for bank information during partial-panel flying.
Why the other options are wrong
- B. The attitude indicator is typically vacuum-driven and will fail or become unreliable.
- C. The heading indicator is also usually vacuum-driven and will be affected.
- D. The VSI is a static-pressure instrument unrelated to the vacuum system, but it does not indicate bank.
Vacuum vs Electric Instruments
Attitude and heading indicators are commonly vacuum-driven, while the turn coordinator is electric, making it a critical backup source for bank information during vacuum failures.
- Vacuum failure disables AI and HI in typical light aircraft
- Turn coordinator remains functional using aircraft electrical power
- Partial-panel scenarios require use of turn coordinator plus other cross-checks
Memory trick: Vacuum powers AI/HI; electricity powers the turn coordinator.