Pressure and altimetry · Question 12 of 12
You take off with QNH 1 020 hPa and fly without resetting into an area with QNH 1 005 hPa. The altimeter shows 3 000 ft. Approximately how high are you above sea level?
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Answer
- B About 2 550 ft
Explanation
The pressure difference is 15 hPa, which at about 30 ft per hPa is roughly 450 ft. Because you are flying into the low, the set pressure level lies lower: you are about 450 ft lower than indicated. Over terrain this can cost obstacle clearance.