FAA Aviation Mechanic Airframe (AMA)Airframe Electrical and InstrumentsMedium
An aircraft is flying a heading of due east and begins a gentle acceleration while maintaining altitude in the Northern Hemisphere. Due to acceleration error inherent in the magnetic compass, the compass will temporarily indicate a turn toward which direction?
- ANorth
- BNo change in indication occurs
- CEast, but with increasing oscillation
- DSouth
Show answer & explanationAnswer & explanation
Correct answer: A. North
Acceleration/deceleration error (ANDS: Accelerate North, Decelerate South) causes the compass to falsely indicate a turn toward north when accelerating on east or west headings in the Northern Hemisphere, due to pendulous mounting and magnetic dip forces acting on the compass card.
Why the other options are wrong
- B. Acceleration error is a well-documented compass characteristic and does cause a temporary false indication.
- C. The error is a predictable directional shift, not random oscillation.
- D. This is the deceleration error result, not acceleration.
Acceleration/Deceleration Error (ANDS)
A magnetic compass error occurring on east/west headings in which acceleration causes an apparent turn toward north and deceleration causes an apparent turn toward south, due to compass card pendulosity and magnetic dip.
- ANDS = Accelerate North, Decelerate South
- Error is most pronounced on east/west headings
- No error occurs on north/south headings during acceleration
- Caused by pendulous mounting of the compass card combined with vertical dip component
Memory trick: ANDS: Accelerate North, Decelerate South — remember it like a compass speeding north when you step on the gas.