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The altimeter of an aircraft provides indications from 0 - 30 000 ft. The aircraft is on a position of known elevation at the airfield and the altimeter is set to the local QNH. The altimeter will read the elevation of that point…

  • A

    plus the height of the altimeter from the ground with a +/- 80 ft tolerance.

  • B

    plus the height of the altimeter from the ground with a +/- 60 ft tolerance.

  • C
    +/- 25 ft tolerance.
  • D
    +/- 80 ft tolerance.

ICAO Doc. 8168 (PANS-OPS) Vol 3

A serviceable altimeter indicates the elevation of the point selected, plus the height of the altimeter above this point,
within a tolerance of:

a) ±20 m or 60 ft for altimeters with a test range of 0 to 9000 m (0 to 30 000 ft); and

b) ±25 m or 80 ft for altimeters with a test range of 0 to 15 000 m (0 to 50 000 ft).

Very simply, you only need to remember that it is ± 60 ft for altimeters up to 30 000 ft, and a little less accurate for altimeters that can go higher, ± 80 ft for altimeters up to 50 000 ft.

Of course, with our aircraft being sat on the ground, the altitude measured would be the ground elevation plus the height on the altimeter off the ground, plus/minus any error (within the tolerance).

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