QNH

[Bealzebub]

High elevation airfields issue QNH settings.

The (UK) met office defines QNE as follows : "QNE is only used when the pressure is so low or so high that the altimeter subscale will not go up or down far enough to select the correct QFE - thus a pressure is assigned so that the altimeter reads a specific (known) height when the aircraft is on the ground - that is the QNE."

QNH is defined thus : "QNH is used to set the altimeter to read the actual height above sea level in the local area. This is also passed by the local ATC and so when the aircraft is on the ground with QNH set, the altimeter will show the height of the airfield."

Normally a high elevation airfield would issue a QNH the same as any other airfield. The current metar for La Paz Bolivia (elev 13,355ft) at the time of writing is :
2006/02/25 22:00
SLLP 252200Z 14004KT 9999 FEW017 FEW020CB SCT070 BKN200 10/02 Q1033

The last figure being the QNH.

Nairobi Kenya (elev 5327ft):
2006/02/25 21:00
HKJK 252100Z 01005KT 9999 FEW020 20/13 Q1020 NOSIG

The last figure being the QNH

Mexico city (elev 7341ft):
2006/02/25 21:45
MMMX 252145Z 31010KT 7SM FEW030 26/01 A3024 RMK 8/500 HZY.

A3024 being the altimeter settings in inches of mercury ( and hundredths) or as we know it the QNH.


Quito Equador ( elev 9223ft):
2006/02/25 22:00
SEQU 252200Z 34008KT 9999 BKN040 BKN100 15/12 Q1023 NOSIG.

The last figure being the QNH.

All these airfields are between 5327ft elev' and 13,355 ft elev.

These are the metar reports, the ATIS information and the altimeter settings being passed to arriving and departing aircraft.