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The subscale of an altimeter is set to 1013.2 hPa. The aircraft has to land on a point with an elevation of 290 feet where the QNH is 1023 hPa. Assuming that 1 hPa corresponds to 27 ft, the reading on the altimeter on the ground will be:
  • A
    11 ft
  • B
    560 ft
  • C
    -10 ft
  • D
    20 ft

The question states that the current altimeter setting of 1013.2 will not be changed upon landing to the local QNH of 1023. This means that a lower pressure value is set on the altimeter. If we set the QNH of 1023 hPa on the altimeter the altimeter would read the airports elevation of 290 ft.

1023 – 1013 = 10 hPa
10 x 27 = 270 feet

We now need to subtract 270 ft from 290 ft because we go to a lower pressure value set on our altimeter subscale. 290 ft - 270 ft = 20 ft will be indicated on the ground with 1013.2 hPa still set.

Note: According to the new syllabus (EASA 2020) a barometric lapse rate of 30 ft /hPa should be used. However, if the question text indicates a different lapse rate, that is the one you are expected to use.

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