FAA Instrument Rating Airplane (IRA)Flight Instruments and SystemsEasy
A pilot flying with a vacuum-driven attitude indicator notices the vacuum gauge has dropped to zero due to a pump failure. What should the pilot expect regarding the attitude indicator's behavior?
- AThe heading indicator will fail first while the attitude indicator remains fully reliable
- BIt will gradually topple over several minutes, giving increasingly erroneous pitch and bank indications
- CIt will continue operating normally because attitude indicators have independent electrical backup power
- DIt will fail instantly and display a red warning flag
Show answer & explanationAnswer & explanation
Correct answer: B. It will gradually topple over several minutes, giving increasingly erroneous pitch and bank indications
Most attitude indicators are vacuum (or pressure) driven and rely on airflow to spin the gyro; without vacuum, the gyro spins down slowly, causing the indicator to gradually give false and increasingly unreliable pitch/bank information rather than failing instantly.
Why the other options are wrong
- A. Both instruments are typically vacuum-driven together, so both degrade, not just one.
- C. Standard vacuum attitude indicators are not electrically powered backups; this describes a different instrument architecture.
- D. There is no instant failure or flag on most vacuum attitude indicators; failure is gradual.
Vacuum Pump Failure Effect
Loss of vacuum causes the gyro-driven attitude indicator to slowly spin down, producing gradually increasing erroneous pitch/bank indications rather than an immediate failure.
- Vacuum gauge reading zero indicates pump failure
- Attitude indicator errors develop slowly and can be mistaken for real attitude changes
- Cross-check with electric turn coordinator to detect the failure
Memory trick: A dying vacuum pump makes the gyro 'die slowly,' not instantly.