Definition
In the Aviation Instructor's Handbook, magnetic compass errors is used as a classic example of a topic that lends itself to mnemonic learning. The specific errors of the magnetic compass — variation, deviation, dip, acceleration/deceleration error, and northerly/southerly turning error — are commonly taught using the mnemonic 'VDMONA' or similar memory aids so students can recall the full set without omission.
Plain English
It's the list of ways a magnetic compass can give a misleading reading in flight. Instructors use it as a teaching example because it's a tidy group of items that students can memorize using a short memory trick.
Context Anchor
Encountered when learning basic navigation, instrument scanning, and memory aids such as compass-turning and acceleration-error mnemonics.
Derivation
Magnetic comes from magnet, referring to the compass aligning with Earth’s magnetic field. Compass comes from an older word meaning to measure or go around. Error comes from a word meaning to wander, which fits here because the compass indication can wander away from the heading the pilot expects.
Why Pilots Care
Uncorrected compass errors cause heading deviations that can lead to navigation mistakes or loss of situational awareness, especially in instrument conditions.
Grounding Statement
When the airplane turns or changes speed, the compass card can lag, lead, or swing, even though the airplane itself is behaving normally.
Intuition Check
Do not read errors here as random mistakes or a broken compass. Magnetic compass errors are known, repeatable limits in how a normal compass indicates direction.
Example Sentence 1
The instructor introduced a mnemonic to help the student remember all of the magnetic compass errors before the next cross-country flight.
Example Sentence 2
In the turn to final, the instructor reminded the student to lead the rollout by half the bank angle to offset magnetic compass errors.