A pilot flying a compass heading of due north in the Northern Hemisphere begins a turn to the east. Due to magnetic dip, how will the magnetic compass initially indicate the turn?
- AIt will lag and briefly indicate a turn in the opposite direction
- BIt will read accurately throughout the turn
- CIt will remain fixed on north until the turn is complete
- DIt will lead the turn and show a greater rate of turn than actual
Show answer & explanationAnswer & explanation
Correct answer: A. It will lag and briefly indicate a turn in the opposite direction
Northerly turning error is caused by magnetic dip acting on the compass card's pendulous mounting. When turning from a heading near north, the compass initially indicates a turn in the opposite direction of the actual turn before catching up, because the dip force tilts the card the wrong way relative to the turn. This error is greatest near north and south headings and is called 'lag' when starting from a northerly heading.
Why the other options are wrong
- B. Magnetic compasses have significant turning errors near north/south headings due to dip, so accuracy is not maintained.
- C. The compass does move, just initially in the wrong apparent direction.
- D. Leading (showing greater turn than actual) occurs when turning from a southerly heading, not northerly.
Northerly Turning Error
A magnetic compass error caused by dip where, when turning from a heading near north, the compass initially indicates a turn opposite to the actual direction of turn.
- Caused by magnetic dip acting on the pendulously mounted compass card
- Greatest near north/south headings, minimal near east/west
- Remembered by mnemonic 'ANDS': Accelerate North, Decelerate South
Memory trick: ANDS: Accelerate North, Decelerate South — and turns from North Lag, from South Lead