compass errors

This question describes the situation where you as on an easterly heading and begin ("roll into") a right turn (towards the south). It does not ask about what happens when you're already in the turn and are approaching southerly headings. The difference matters!

Using the Magnetic Compass

• If on a northerly heading and a turn is made toward east or west, the initial indication of the compass lags or indicates a turn in the opposite direction. This lag diminishes as the turn progresses toward east or west where there is no turn error.
• If on a southerly heading and a turn is made toward the east or west, the initial indication of the compass needle will indicate a greater amount of turn than is actually made. This lead also diminishes as the turn progresses toward east or west where there is no turn error.
• If a turn is made to a northerly heading from any direction, the compass indication when approaching north lags behind the turn. Therefore, the rollout of the turn is made before the desired heading is reached.
• If a turn is made to a southerly heading from any direction, the compass indication when approaching southerly headings leads the turn. Therefore, the rollout is made after the desired heading is passed. The amount of lead or lag is maximum on the north-south headings and depends upon the angle of bank used and geographic position of the aircraftwith regard to latitude.
• When on an east or west heading, no error is apparent while entering a turn to north or south; however, an increase in airspeed or acceleration will cause the compass to indicate a turn toward north; a decrease in airspeed (a deceleration) or a decrease in acceleration (that is, still accelerating, but more slowly) will cause the compass to indicate a turn toward south.
• If on a north or south heading, no error will be apparent because of acceleration or deceleration.

Incorrect Answer Choices:

• "The compass will remain on east for a short time, then gradually catch up to the magnetic heading of the aircraft" is incorrect. This would be true if we started on a NORTHERLY heading and started a turn to the east or west. But, the question does not ask about this.
• "The compass will initially indicate a turn to the left." is incorrect. While this is is roughly similar sounding to the east-west acceleration/deceleration error of magnetic compasses, this is not relevant to this question

On an east (090°) heading in the Northern Hemisphere, the magnetic compass shows no turning lead/lag at the instant you begin a coordinated turn toward north or south. If the entry to a standard-rate right turn is smooth and airspeed is held steady (minimizing acceleration error), the compass indication tracks the actual turn reasonably well. As the turn later approaches southerly headings, the compass tends to lead (southerly turning error), but that happens after entry and is not part of the question. Thus, during roll-in from an easterly heading, the indication should be the approximate correct magnetic heading.

CORRECT: The compass will indicate the approximate correct magnetic heading if the roll into the turn is smooth.

The compass will indicate the approximate correct magnetic heading if the roll into the turn is smooth.Entry from east (or west) is the “zero turning-error” condition: the dip-induced turning error appears primarily when starting from, or approaching, north/south. Keep the roll coordinated and the speed stable to avoid acceleration-induced swings; the compass then follows the right turn closely during roll-in.

Incorrect: The compass will remain on east for a short time, then gradually catch up to the magnetic heading of the aircraft.

That “lag-then-catch-up” behavior describes northerly turning error when initiating a turn from a northerly heading. From an easterly heading, the entry indication should be essentially correct, provided the roll-in is coordinated and there is no meaningful acceleration or deceleration.

Incorrect: The compass will initially indicate a turn to the left.

An opposite-direction swing is associated with starting a turn from north (lag) or with acceleration/deceleration artifacts on east–west headings. With a smooth roll-in at constant speed from an easterly heading, the compass should show a right turn, not a left turn.