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stab trim
7th Aug 2001, 16:58
We are about to install EGPWC with provision for calculation of geometric altitude, thus enabling us to operate in QFE environment. Anyone who can tell me what QFE stands for. Also, are the letters QFE an abbreviation ?
As I’m in engineering, not a pilot, I could like to hear from someone knowledgeable where or when we are in QFE environment.

What are QNH and QNE, as opposed to QFE ? Explanations appreciated.

Nick Figaretto
7th Aug 2001, 17:24
QNH environment: All altitudes expressed relative to MSL (mean sea level). Altimeters are set to a given pressure (the QNH), and the altimeter in the aircraft, will read the aerodrome elevation when the AC is on the ground.

QFE environment: All altitudes expressed relative to height above aerodrome level. Altimeters are set to a given pressure (the QFE), and the altimeter in the aircraft, will read 0 when the AC is on the ground.

See also the discussion where does "QNH" come from

Nick.

[ 07 August 2001: Message edited by: Nick Figaretto ]

wysiwyg
7th Aug 2001, 18:46
QNE - isn't that when 1013.2HPA (29.92" for the yanks) is set?

None
7th Aug 2001, 22:32
Stab Trim,
Are you saying your new software update to EGPWS will allow you to keep it activated on arrival to a place using QFE? Our's will not.

Genghis the Engineer
8th Aug 2001, 11:02
QFE (from the old Morse "Q" codes) doesn't stand for anything, it is one of the three standard altimeter settings: -

QNH - set to give altitude AMSL, either for a specific airfield (airfield QNH) or a local average (regional QNH). The former is usually used for airfield departures, the latter for safe separation of transiting traffic at lowish levels.

QNE - 1013.25mb, only normally set above FL30.

QFE - set to give height above a datum point on an airfield, which is usually the threshold of the primary runway. It is used when transiting the overhead of an airfield, or when operating with the intention of a landing at that airfield.

QFE is largely a UK habit, probably because most other countries have too many airfields whose QFEs would be off the scale of a common or garden altimeter. It is however a useful tool, since for airfield approaches and suchlike, it removes any need for in-flight calculations of height, and thus aircrew workload (albeit only slightly). It does however confuse visiting American pilots since they have only just about grasped millibars / heptopascals, and the idea of setting anything but QNH (which they simply call "altimeter") throws them. Not their fault poor chaps, just the way they do things over there.

Oh yes, and the Royal Navy hardly ever uses QFE, they operate entirely with QNH. Not sure why, any ideas? :p

G

Chilli Monster
8th Aug 2001, 14:07
wysiwyg & Genghis

You've got QNE slightly wrong. It's not 1013.2 (That is termed the Standard Altimeter Setting) BUT (and this is the concept people find hard to grasp) it's the LEVEL indicated when 1013.2 is set. Used mainly in high or mountainous environments where you want an indication of height as a landing datum (much the same as QNH) but with the advantage that when the pressure is low (most altimeters can't go below 950mb) it gives a reference that is available to use.

CM

stab trim
8th Aug 2001, 17:39
Thanks a lot for valuable input from all of you.

None. Quote Are you saying your new software update to EGPWS will allow you to keep it activated on arrival to a place using QFE? Our's will not. Unquote

To comment your question, pls be advised I’m referring to B737NGs with GPS installed. It’s my understanding the answer to yr question is yes. With the new updated P/N we are installing, we are allowed to remove a QFE limitation from the AFM. With the AFM limitation, we are not allowed ‘to fly in a QFE environment without disabling the enhanced features of the ground proximity warning system’, as Boeing express this. As I understand this, the updated EGPWC calculates geometric altitude, or true height above sea level, which allows for continuous EGPWS operation in QFE environment.

At this time I do not know the situation for other a/c types. Even though I find this information exchange very useful, I hope you’ll understand when I prefer not to go into more details here on the forum, as I’d hate to infringe Boeings possibly proprietary documentation.