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When using the magnetic compass in NORTHERN HEMISPHERE flying, which two errors must be considered?
Choices
Variation and deviation only.
Variation/deviation are corrected by computation, not flight error.
✓ Acceleration error (ANDS.correct
Accelerate North, Decelerate South: when accelerating on east/west heading, the compass swings toward north; decelerating swings south) and turning error (UNOS — Undershoot North, Overshoot South). Magnetic dip causes two compass errors in flight: ACCELERATION (ANDS) — accelerate east/west and the compass moves toward N; decelerate and it moves toward S. TURNING ERROR (UNOS) — turning to N from E or W, undershoot the rollout (lead by ~15° + half latitude); turning to S, overshoot by the same. Errors are zero on E/W headings (turning) and on N/S headings (acceleration).
Parallax error and refraction error.
Parallax/refraction don't apply to magnetic compass.
Magnetic dip is irrelevant in normal operations.
Magnetic dip is the cause of both flight errors.
Why
Accelerate North, Decelerate South: when accelerating on east/west heading, the compass swings toward north; decelerating swings south) and turning error (UNOS — Undershoot North, Overshoot South). Magnetic dip causes two compass errors in flight: ACCELERATION (ANDS) — accelerate east/west and the compass moves toward N; decelerate and it moves toward S. TURNING ERROR (UNOS) — turning to N from E or W, undershoot the rollout (lead by ~15° + half latitude); turning to S, overshoot by the same. Errors are zero on E/W headings (turning) and on N/S headings (acceleration).
FAA source: PHAK Ch 8; PHAK Chapter 8 — Flight Instrumentsbrowse the reference library →
Original study question written for this course — representative of FAA knowledge-test topics, not an actual current FAA exam question.