FAA Instrument Rating Airplane (IRA)Flight Instruments and SystemsEasy
An aircraft in the Northern Hemisphere is turning from a heading of North to a heading of East. As the bank is established, the magnetic compass will initially:
- AIndicate a turn toward West before slowly catching up to the actual heading
- BIndicate the turn accurately from the start
- COvershoot and show a heading past East
- DFreeze on North until the turn is complete
Show answer & explanationAnswer & explanation
Correct answer: A. Indicate a turn toward West before slowly catching up to the actual heading
Due to magnetic dip in the Northern Hemisphere, a turn from a northerly heading causes the compass card to initially lag and swing opposite the direction of turn before it begins to indicate correctly. This is a classic turning error taught as 'compass lags when turning from north.'
Why the other options are wrong
- B. Compass turning errors make the indication inaccurate during the roll, especially near North and South.
- C. Overshooting past the target heading is characteristic of turns from a southerly heading, not northerly.
- D. The compass does not freeze; it actively but incorrectly indicates a reverse-direction swing.
Compass Turning Error
Magnetic dip causes the compass to lag when turning from a northerly heading and lead (overshoot) when turning from a southerly heading in the Northern Hemisphere.
- Undershoot North, Overshoot South (UNOS)
- Errors are greatest near N/S, minimal near E/W
- Caused by vertical component of Earth's magnetic field acting on the compass card
Memory trick: UNOS: Undershoot North, Overshoot South.