FAA Instrument Flight Instructor (FII)Instruments and SystemsMedium
After rolling out of a steep 360° turn, a CFII notes that the attitude indicator briefly shows a slight climb and bank that were not commanded. This momentary error is most likely the result of
- Astatic port icing affecting the pitch reference
- Bvacuum pump failure
- Ca failed erection mechanism requiring instrument replacement
- Dgyroscopic precession from gimbal friction during the turn
Show answer & explanationAnswer & explanation
Correct answer: D. gyroscopic precession from gimbal friction during the turn
The attitude indicator's gyro is subject to small precession errors caused by friction in the gimbals, which become most noticeable following turns, particularly steep turns of 180° or more. These errors are normal, self-correct within a minute or so via the erecting mechanism, and do not indicate a malfunction.
Why the other options are wrong
- A. The attitude indicator is a gyroscopic instrument and is not affected by the static system.
- B. A vacuum failure would cause the instrument to slowly and progressively fail, not a brief, self-correcting error.
- C. This is a normal, expected error, not a failure requiring maintenance.
Attitude Indicator Precession Error
Friction within the gimbals of the attitude indicator gyro produces small, temporary pitch and bank errors after turns, which self-correct through the erecting mechanism.
- Most noticeable after turns greater than 180°
- Self-corrects within about 1 minute
- Caused by gimbal friction precession, not instrument failure
- Distinct from total instrument failure from a vacuum or power loss
Memory trick: Turn hard, gyro flinches — but it forgives itself in a minute.