FAA Private Pilot Airplane (PAR)Aerodynamics and Aircraft SystemsMedium
While climbing out after takeoff, a pilot notices the vacuum-driven attitude indicator briefly shows a slight climb and a slight bank to the left that does not match the airplane's actual straight climb attitude, before the indication self-corrects within a minute. What is the most likely explanation for this temporary error?
- AA blocked static port affecting the pitot-static instruments
- BA failing vacuum pump causing the gyro to spin down
- CMagnetic dip affecting the gyro's alignment with true north
- DNormal precession error inherent to vacuum-driven attitude gyros during pitch changes
Show answer & explanationAnswer & explanation
Correct answer: D. Normal precession error inherent to vacuum-driven attitude gyros during pitch changes
Attitude indicators, especially older vacuum-driven models, have small inherent errors called precession that can cause brief, minor false indications during rapid pitch or roll changes, such as acceleration during climb-out. These errors are normal and self-correct within a minute or two as the gyro re-erects itself; they are not typically caused by pump failure or magnetic effects.
Why the other options are wrong
- A. The attitude indicator is gyroscopic, not part of the pitot-static system, so static port issues are unrelated.
- B. A failing vacuum pump would cause a gradual, worsening degradation, not a brief self-correcting error.
- C. Magnetic dip affects magnetic compasses, not gyroscopic attitude indicators.
Attitude Indicator Precession Error
A small, temporary and self-correcting error in gyroscopic attitude indicators that can occur during rapid pitch or bank changes, such as during takeoff acceleration or steep turns.
- Considered a normal characteristic, not a malfunction, if brief and self-correcting
- Different from a failing vacuum pump, which causes a slow, worsening, uncorrected error
- Most noticeable during acceleration, deceleration, or steep turns
Memory trick: A quick wobble that fixes itself is just gyro growing pains.