QNH and QFE: What Your Altimeter Shows

With the pressure setting on the altimeter you decide what the indicated height refers to. Depending on the setting, you read a different value at the same place.

The terms in SERA

• Altitude is the vertical distance of a level or point from mean sea level (MSL).
• Height is the vertical distance of a level or point from a specified datum.
• A flight level is a surface of constant atmospheric pressure, related to 1013.2 hPa.

What QNH, QFE and 1013.2 hPa show

QNH

With QNH set, the altimeter shows altitude above mean sea level. On the aerodrome you read the aerodrome elevation.

QFE

QFE is the atmospheric pressure at aerodrome elevation. With QFE set, the altimeter shows height above the QFE reference datum, so it reads zero there. Once you are cleared to land and are flying the approach using QFE, the height is given above aerodrome elevation. For precision approach runways, and for instrument runways whose threshold is 2 m (7 ft) or more below the aerodrome elevation, it refers to the threshold elevation.

1013.2 hPa

With the standard setting of 1013.2 hPa, the altimeter can indicate flight levels. According to the FAA handbook, it then shows pressure altitude, the height above a theoretical datum plane where the pressure is 1013.2 hPa.

Where you get QNH and QFE

A METAR contains only the QNH, never the QFE. It is reported in whole hectopascals, with four digits and rounded down: Q1017 means QNH 1017 hPa, and a QNH of 995.6 hPa appears in the METAR as Q0995.

Air traffic control gives you the QNH, unless you have already received it, in three cases: in the descent clearance when you are first cleared to an altitude below the transition level, in the approach clearance or the clearance to enter the traffic circuit, and in the taxi clearance for departing aircraft. You get a QFE on request or regularly under local arrangements. You always read back altimeter settings and transition levels to the controller.

Transition altitude and transition level

The transition altitude is the altitude at or below which the vertical position of an aircraft is controlled by reference to altitudes. The transition level is the lowest flight level available for use above the transition altitude.

Where a transition altitude is established, the vertical position is given in altitudes at or below the transition altitude and in flight levels at or above the transition level. In the transition layer: when climbing you give flight levels, when descending you give altitudes.

What the EASA syllabus says

EASA lists QNH and QFE in the abbreviations for Part-FCL as “Altimeter sub-scale setting to obtain elevation when on the ground” and “Atmospheric pressure at aerodrome elevation”. Under Instrumentation, the PPL(A) theoretical knowledge syllabus lists “The different barometric references (QNH, QFE and 1013.25)” for the altimeter. How a pressure gradient affects the reading is explained on the related page about altimeter errors.