FAA Flight Instructor Airplane (FIA)Aircraft Systems and InstrumentsHard
An airplane is equipped with a standby vacuum system in addition to the engine-driven vacuum pump. During a simulated vacuum pump failure, a CFI asks the student to activate the standby system. What is the primary function of this system?
- ATo supply backup electrical power to the attitude indicator if the battery fails
- BTo provide backup hydraulic pressure for landing gear extension if the primary pump fails
- CTo pressurize the pitot-static system as a backup if the pitot tube becomes blocked
- DTo provide an alternate source of vacuum, often using engine manifold pressure, to continue powering gyroscopic flight instruments
Show answer & explanationAnswer & explanation
Correct answer: D. To provide an alternate source of vacuum, often using engine manifold pressure, to continue powering gyroscopic flight instruments
A standby vacuum system typically uses engine manifold pressure (via a check valve arrangement) as an alternate vacuum source to continue driving vacuum-powered gyroscopic instruments, such as the attitude indicator and heading indicator, if the primary engine-driven vacuum pump fails.
Why the other options are wrong
- A. This describes a backup electrical system, not a vacuum system.
- B. This describes hydraulic backup systems for landing gear, a different system entirely.
- C. This describes pitot-static backup systems, unrelated to vacuum.
Standby Vacuum System
A backup vacuum source, often utilizing engine manifold pressure through a check valve, that continues to power vacuum-driven gyroscopic instruments if the primary vacuum pump fails.
- Commonly used in light single-engine aircraft as a low-cost redundancy
- Draws vacuum from manifold pressure differential, most effective at higher power settings
- Activated manually by the pilot via a valve or switch when primary vacuum fails
Memory trick: When the pump quits, the manifold takes the shift