FAA Aviation Mechanic Airframe (AMA)Airframe Electrical and InstrumentsHard
A vacuum-driven attitude indicator experiences small precession errors during normal operation that must be continuously corrected to keep the gyro's spin axis vertical. Which mechanism inside the instrument automatically applies this correcting torque?
- APendulous vanes that redirect the exhaust airflow to erect the gyro
- BA synchro transmitter that senses gyro drift
- CA rate gyro coupled to the attitude indicator
- DA flux valve sensing element
Show answer & explanationAnswer & explanation
Correct answer: A. Pendulous vanes that redirect the exhaust airflow to erect the gyro
Pendulous vanes located at the air exhaust ports of the gyro housing hang plumb under gravity. When the gyro tilts from vertical, the vanes partially cover different exhaust ports, unevenly deflecting the exiting air and creating a precessing force that erects the gyro back to vertical. This is a purely mechanical, self-correcting erection system.
Why the other options are wrong
- B. Synchro transmitters are used in remote-indicating systems, not gyro erection.
- C. A rate gyro is the operating principle of the turn coordinator, not the erection mechanism of the attitude indicator.
- D. Flux valves sense magnetic heading, unrelated to attitude gyro erection.
Pendulous Vane Erection System
A mechanical system in vacuum-driven attitude indicators using gravity-controlled vanes at the air exhaust ports to correct gyro precession and maintain vertical alignment.
- Vanes hang under gravity and shift with gyro tilt
- Unequal air exhaust creates a correcting precession torque
- Continuously erects the gyro to true vertical during normal flight
Memory trick: Pendulous vanes swing like tiny weights steering the airflow to keep the gyro upright