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An airfield has an elevation of 5500 ft and the current QNH is 1021 hPa. What is the pressure altitude at this airfield?

  • A

    5260 ft

  • B

    5740 ft

  • C

    5500 ft

  • D

    5020 ft

Pressure altitude is the altitude indicated on an altimeter when the subscale is set to 1013.25 hPa (standard pressure).

To convert from airfield elevation (referenced to QNH) to pressure altitude, the difference between QNH and standard pressure (1013 hPa) is applied. 

The correction factor is 30 ft per hPa.

QNH = 1021 hPa. Deviation from standard = 1021 minus 1013 = +8 hPa above standard. If QNH is HIGHER than 1013, the actual pressure is greater than standard for that elevation, meaning the pressure altitude is LOWER than the elevation.

Altitude correction = 8 x 30 = 240 ft subtracted from elevation. 

Pressure altitude = 5500 -240 = 5260 ft

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