FAA Instrument Flight Instructor (FII)Instruments and SystemsHard
An aircraft is flying a heading of due north in the Northern Hemisphere when the pilot smoothly accelerates. Due to magnetic dip, the magnetic compass will temporarily indicate a turn
- Atoward the south
- Btoward the west
- Ctoward the east
- Dtoward the north, exaggerating the correct heading
Show answer & explanationAnswer & explanation
Correct answer: A. toward the south
The mnemonic ANDS (Accelerate North, Decelerate South) describes acceleration errors caused by magnetic dip in the Northern Hemisphere. When accelerating on a northerly heading, the compass card temporarily swings and indicates a turn toward the south, even though the aircraft is actually still flying straight north.
Why the other options are wrong
- B. Same as above; westward indication is not the acceleration error pattern for a north heading.
- C. East/west errors are associated with turning through those headings, not acceleration on a north heading.
- D. An exaggerated northward indication is not consistent with the known acceleration error pattern.
Magnetic Compass Acceleration Error (ANDS)
Due to magnetic dip, the compass gives false turn indications during acceleration/deceleration on northerly/southerly headings, remembered by the mnemonic ANDS: Accelerate North, Decelerate South.
- ANDS = Accelerate North, Decelerate South (Northern Hemisphere)
- Errors are most pronounced on headings of north and south
- Errors are minimal on east/west headings
- Caused by pendulous mounting of the compass card responding to dip
Memory trick: ANDS: Accelerate North, Decelerate South.