FAA Flight Instructor Airplane (FIA)Aircraft Systems and InstrumentsHard
A CFI is explaining magnetic compass errors to an instrument student. While flying a constant heading of due west in the northern hemisphere and accelerating, how will the compass momentarily indicate, and why?
- AIt will show no error since acceleration errors only occur on north and south headings
- BIt will indicate a turn toward the south due to acceleration error on westerly headings
- CIt will indicate a climb due to the pendulous mounting of the compass card
- DIt will indicate a turn toward the north due to acceleration error on westerly headings
Show answer & explanationAnswer & explanation
Correct answer: A. It will show no error since acceleration errors only occur on north and south headings
Acceleration and deceleration errors (remembered by ANDS: Accelerate North, Decelerate South) are maximum on headings of north and south and are absent on east and west headings, where the compass is most accurate during acceleration/deceleration. On west heading, no acceleration error occurs; only turning errors would be relevant on that heading.
Why the other options are wrong
- B. Incorrect direction and incorrect heading; acceleration errors are absent on east/west headings.
- C. The compass does not indicate climbs; this confuses it with other instrument errors.
- D. Acceleration errors do not occur on west headings; this describes a north-heading error incorrectly applied.
Compass Acceleration/Deceleration Error (ANDS)
Due to pendulous mounting, the magnetic compass shows a false turn indication during acceleration or deceleration, maximum on north/south headings and zero on east/west headings.
- ANDS: Accelerate North, Decelerate South
- Error is zero on east and west headings
- Caused by compass card's pendulous suspension and dip
Memory trick: ANDS: Accelerate North, Decelerate South; zero on East/West