QNH and QFE basics

This subject has a lot more to it than this page, and this is just a very low level overview.

QFE = Is the atmospheric pressure at the airfield level. The Altimeter will read 0 ft when on the ground at the airfield

 This is used when in proximity of home or destination airfield.

Reading from this setting is referred to as HEIGHT

QFE is very good for new pilots who are remaining in the circuit around an airfield and keeps things simple for that task.

QNH = The pressure measured at station then reduced down to mean sea level pressure. When set on your altimeter it will read your ALTITUDE. Sat on the tarmac at your airfield the altimeter will display the airfields elevation above mean sea level.

This is the most commonly used pressure setting in the commercial world. Its probably the most useful setting to have, as nearly all aviation references to elevation are in relation to mean sea level. The mountain peaks on a map, airfield elevation, target elevation, minimum safe altitudes en route etc.   QNH is given as a regional pressure setting and should be updated with new ones if you leave its area of reference into a new QNH pressure region.

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So, if going for a flight, the pilot would establish the QNH and the QFE before take-off. If there is no radio controller or ATIS to provide detail, then the pilot can set the altimeter to “0” on the ground to find the QFE.  If you know the height of the airfield above sea-level, you can calculate the QNH.

Example:

Perth is 400 Ft above sea level.

Roughly speaking 1 millibar is 30 feet. Dividing the 400 feet by 30 gives 14 (rounded up)

Therefore If QFE is 1004, the QNH would be (1003 + 14) = 1017

Here (on the ground), the altimeter was set to QFE (reading 0 feet). By looking at the small window just above the “3” you can see the QFE setting that day was 1003 hectopascals.

This was the pressure for that day. The following day, the QFE could have been completely different. The Setting is changed by the dial button (bottom left, beside the “6”)

If flying circuits (i.e not leaving the airfield) then this would have been left as it was, unless instructed of change.
If the pilot was to leave the area, the altimeter would be manually changed in flight from 1003 to 1017 to reflect the QNH.

When the pilot returns to the same airfield, then the altimeter would be reset back to QFE from QHN. This ensures all aircraft fly the circuit at the same height.

SO:  (especially for the Exams)
QFE = Height (used within airfield parameters)
QNH = Altitude  (Used for travelling between airfields)