A pilot notes that their aircraft's magnetic compass reads 090 degrees while flying over an area with a magnetic variation of 5 degrees West. What is the true heading of the aircraft?
- A090 degrees
- B100 degrees
- C095 degrees
- D085 degrees
Show answer & explanationAnswer & explanation
Correct answer: D. 085 degrees
To convert magnetic heading to true heading when variation is West, you subtract the variation. Magnetic Heading (090°) - West Variation (5°) = True Heading (085°). East is Least (subtract), West is Best (add). However, this rule applies when converting True to Magnetic. When converting Magnetic to True: West variation means True is less than Magnetic (subtract), East variation means True is more than Magnetic (add). So 090 - 5 = 085.
Why the other options are wrong
- A. Incorrect. This would be correct if there was no magnetic variation.
- B. Incorrect. This is a common error of applying the 'West is Best' rule incorrectly when converting Magnetic to True.
- C. Incorrect. This would be correct if the variation was 5 degrees East and converting from True to Magnetic, or if converting Magnetic to True with East variation.
Magnetic Variation
The angular difference between true north and magnetic north at a specific location, indicated on aeronautical charts by isogonic lines.
- Expressed in degrees East or West.
- East variation means magnetic north is east of true north.
- West variation means magnetic north is west of true north.
Memory trick: East is Least (subtract from True to get Magnetic), West is Best (add to True to get Magnetic). For Magnetic to True, reverse it: East + True, West - True.