FAA Instrument Rating Airplane (IRA)Flight Instruments and SystemsMedium
While flying straight and level on a heading of West in the Northern Hemisphere, the pilot smoothly accelerates the airplane. Without cross-checking other instruments, the magnetic compass will temporarily indicate a turn toward:
- AWest (no error occurs on this heading)
- BEast
- CNorth
- DSouth
Show answer & explanationAnswer & explanation
Correct answer: C. North
On easterly or westerly headings, acceleration and deceleration errors dominate. The mnemonic ANDS (Accelerate North, Decelerate South) applies in the Northern Hemisphere: accelerating on any east or west heading makes the compass swing toward North.
Why the other options are wrong
- A. Acceleration error is actually greatest on East/West headings, not absent.
- B. Acceleration/deceleration error only produces apparent turns toward North or South, not East.
- D. South corresponds to deceleration, not acceleration.
Compass Acceleration/Deceleration Error (ANDS)
On east or west headings, acceleration causes the compass to show an apparent turn toward North, and deceleration causes an apparent turn toward South.
- ANDS = Accelerate North, Decelerate South
- Error is maximum on E/W headings, zero on N/S headings
- Caused by pendulous mounting of the compass card reacting to inertial forces
Memory trick: ANDS: Accelerate North, Decelerate South.