QNH or QFE ?
 

Excuse the probably daft question, but. When I hear 'altimeter nnnn' or read 'Qnnnn' in a METAR can I always assume that is QNH?

I have not heard a value being explicitly stated as QNH by ATIS, METAR or ATC. I read that QFE may be provided, but I have never encountered it. How would QFE be described in an ATIS transmission? Presumably it is just a fixed offset from QNH?


Thanks

Most countries (and most pilots) do not use QFE. METAR, TAF, VOLMET and ATIS data refer to QNH (or simply 'altimeter') in the US.

I'm not sure from where you are obtaining your information. QFE is no longer the standard (with the exception of the UK military). All pressures provided in official reports by the Met Office or ATC will be QNH and this is the case in a METAR. In addition to the qualification "QNH" the associated term "altitude" is used.

Within the UK and France the pilot may request a QFE from ATC which will be provided and the associated term "height" will be used. Many small UK airfields that do not have ATC but provide for an A/G service QFE is still commonly used but this is slowly changing. UK Helicopter operators usually prefer QFE because it is particularly valuable for setting down on platforms aboard ships and oil rigs etc. I don't know if this is always the case within the UK or elsewhere.

Where pressure is given in a report or passed by ATC the qualification "QNH" or "QFE" always precedes the actual pressure.

Double Barrel,

You don't say which country you are in.

Basically, only the UK - as far as I am aware - really uses QFE.

For one thing, if you were on high ground you won't be able to wind the altimeter down far enough to get it to read QFE! Even in the UK, with Strathaven being 847ft AMSL, we can have this problem. I have even heard that Loganair one time in a deep winter low couldn't even set QNH flying out of Orkney or Shetland one winter, but that is another story!

The Glasgow ATIS, for example - you can listed to it on 0141 887 7449 - specifically gives QNH. There is no mention of QFE. As you say, it is a fixed offset for QFE and is easy to calculate.

The British Microlight Aircraft Association PPL syllabus suggests - but doesn't mandate - the use of QFE on General Skills Tests. Perhaps not a surprise since, as mentioned, it can be impossible to select at times here at Strathaven! So even in the UK it is optional - although you should learn what it is and be able to calculate it for ground exams.

Thanks all. That makes perfect sense. I am not in the UK, but I am using UK-centric reading material. I will stop worrying about QFE! I mis-remembered what I had heard on the local ATIS - it does indeed specify QNH. The various local 'controllers' - towers and approaches seem to use a mix of QNH and the word altimeter

Forget about QFE, it is indeed one more UK peculiarity. OTOH "altimeter setting" is something I never heard (which does not mean all that much, I am not a veteran at all), I think it is US'an parlance. In Belgium, France, Germany, I never heard anything but "QNH is so and so much". Perfectly useable.

Russia, China and some of the -stans still use QFE. Will normally be able to provide QNH to non-local aircraft.

American Airlines used QFE until the late 80s/early 90s. The crews converted QNH to QFE. I heard one Captain had converted a power drill to set the altimeter going into Mexico City.

Spluttered my coffee onto keyboard.....

Adjusted at no cost :ok:

China uses QNH (in Hectopascals).

That's funny :}

Q-Codes;- a brilliant, ground-breaking idea - in 1909. Possibly not that relevant, or even useful, more than a century later? Discuss.
QFE? Ridiculous.

Here's a thread which started almost 10 years ago:

QFE who needs it?

"Altimeter bla bla bla" is similar to QNH in the sense that it refers to mean sea level pressure. The way it is calculated (non-temp corrected) is the same.

But in the US at least, it's expressed in inches (actually 1/100 inches) of mercury, instead of hPa. So "QNH 1013" is identical to "altimeter 2992". Yes, there are conversion charts and any modern altimeter intended for use worldwide has both subscales.

It would be helpful if the US adopted hPa, to avoid situations such as:

'American Jet, descend altitude two thousand, QNH nine nine eight.'
'Amjet, descend altitude two thousand . . . er . . . altimeter . . . QNH . . . two nine nine eight.'

A good example of why, in the UK at least, the correct phraseology is:-

"American Jet descend to altitude 2000 feet QNH 998 hectopascals"

That would require changing a lot of altimeters - over 200,000. It's not going to happen.

No it isn't - it depends on prevailing temperature and pressure range.

2 s

(my bold)

Actually, QNH does NOT depend on the prevailing temperature. It is the airfield level pressure reduced to MSL based on ISA conditions. So in the calculation from airfield-level pressure (which is measured) to QNH, an ISA temperature and temperature profile is assumed. Why? Because your altimeter is also not temperature aware/compensated. So these two errors cancel each other out, and with the correct QNH set, your wheels touch the runway when the altimeter reads airfield/threshold elevation.

There is another Q-code, QFF, where the actual temperature - and even the actual humidity - is taken into account when converting the observed airfield level pressure to the MSL level pressure. So QFF would be the pressure at the bottom of the hole, when you were to dig a hole at the airfield down to MSL. But QFF is fortunately not used in aviation, since the altimeters would need to be temperature compensated: You would not only need to enter the QFF on the subscale, but also the airfield temperature and humidity to ensure your altimeter reads threshold elevation when you touch down. (And note that even QFF makes a few assumptions that may not be valid. One of which is that the temperature lapse rate from airfield elevation to MSL is according to ISA.) https://en.wikipedia.org/wiki/QFF

This means that the difference between QNH and QFE only depends on the airfield elevation. In that sense, it is a fixed value per airfield (although the way the rounding works, there may occasionally be a +/- 1 hPa difference, I guess).

Some of the larger airports with western traffic use QNH, I got QFE from the tower at Wuxi last month. Since the airport elevation is 16 feet and the altimeter is marked off in 20 foot chunks we didn't worry about it.

That would require the altimeter sub-scale to go down to below 770 hPa / 23 inHg. This is my sceptical face. :8

When I left the RAF, all maritime and transport aircraft were using QNH and not as someone else suggested QFE. Quite what they do in basic training and fast jet ops these days I will let others guide you.

Just to put some non UK pilots into the picture of our situation. In the UK most airfields are below 250 ft asl, so it is very easy to set QFE. Whilst in the circuit, it is much easier to fly with the altimeter reading 1000ft, than to have to remember it's 1190 qnh for Carlisle, 1081 qnh for Liverpool, etc etc.
Also for those few odd airfields that have circuit heights of 800 ft or 1500 ft it is so much easier to fly QFE than have to do the maths, especially when you are trying to nail the turn onto final at 600 ft aal.
.

Denham circuit height 750 ft elevation 249ft.
And the 'official' pressure setting to be used in the UK is QNH, with QFE made available on request.

For Carlisle fly 1200 ft QNH, for Liverpool fly 1100 ft. Experienced pilots will judge their turn onto final visually rather than by reference to the altimeter. It's a useful skill to have for when the circuit has to be non-standard shaped for any reason.

At Redhill ATC will instruct to "join overhead at 1,400 QNH" or "descend to 1,200 ft and join right base". Airfield elevation is 222 ft.

Simple

I learned to fly at Denham in the early 80's. We did everything on the QNH, which made the circuit altitude 1,000', very easy. The local flying area is only up to 1,000' QNH, above that you're inside the Heathrow zone, used to be Class A!
Then I went elsewhere and learned that it was easier to 'go with the flow' and use QFE 'cos that's what everyone else was doing.
Later on, I did my instructor course also at Denham and went back to QNH for everything. My first instructor job was on the other side of the airfield, where they insisted we teach QFE! (Just to spite the opposition over the other side, I suspect).
Now I teach aspiring airline pilots all-QNH but go along with old-timer PPLs in our Club who want to use QFE - just so long as we know what we're doing, that's what matters to me.
TOO

Link doesn't work for me but I'm not using Windows.
10 years ago was about the time the CAA designated QNH as the 'official' pressure setting.

This was the original post of that thread:

I am convinced that GA altimeter setting procedures in the UK are far too complicated. Do we really need Regional Settings? Do we really need QFE? The VFR pilot flying in Class G airspace has to reset his or her altimeter several times. Two problems arise: firstly, there is always a chance of setting an incorrect subscale setting every time it is adjusted and secondly, distraction during resetting can draw the pilot’s attention away from other vital tasks, such as lookout and navigational monitoring.

A simpler procedure would be to set local QNH for the whole flight, resetting only if the QNH changes. Rarely does barometric pressure change rapidly, so even if the subscale was not reset at all during the flight the resulting altimeter error would be unlikely to exceed 100 feet or so. Is this significant for VFR flight?

Two further advantages of 'local QNH' flight are improving terrain awareness (which QFE degrades) and reducing the potential for violation of controlled airspace, which in the lower levels usually has a base expressed as an altitude. For student pilots doing circuit work, patterns flown with QNH set would not be difficult to learn. When they came to land away from base, adding field elevation to pattern heights to determine pattern altitude would be part of their pre-flight preparations and could be recorded on the nav log. If a MATZ controller specifies a QFE-based penetration height it is easy to convert this to a QNH-based altitude, rounding up or down to the nearest 100ft.

Finally, it should be noted that commercial airliners around the world fly local QNH below transition altitude and 1013 above it. If it works for the big boys and girls, why not for GA traffic too?

I think that's what the CAA want you to do but because of some diehard civil pilots plus the RAF who insist on using QFE, we're stuck with the present system.
Like TheOddOne, I got into the habit of using QNH only when flying from Denham.

Discorde: I don't think you are going to make much progress on this issue until the "Luddite" flying clubs stop teaching QFE procedures!

@Discorde: thanks for the copy!

Regarding : yes, if "local" QNH were universally available. But it isn't always. So I am afraid "regional QNH" is the least unfortunate that can be done. And it works reasonably well, in reasonably flat areas. As for discarding QFE: yes of course. Those funny Brits are alone to want QFE, anyway; and not even all of them.

There's no such thing as 'Regional QNH' in the UK, but there might be in other countries.
I understand QFE is still used in Russia, China and Mauritius.

There does be "regional QNH" in ICAO definitions. I even know of a few places where it is actually used. But far from me to advocate the concept, I'll not go beyond calling it "the least unfortunate compromise".

And I will agree the UK is not the only third world country to cling to the past.

"There's no such thing as 'Regional QNH' in the UK, but there might be in other countries."
When did Altimeter Settings such as "Orkney 992 hectopascals, Portree 997 hectopascals" stop being used in the UK?

If you don't like QFE then don't use it. Why try and stop others from using it if they so choose?

I use QFE wherever possible but I don't complain about you using QNH? Why does it annoy you so much?

Leave little QFE alone.

Mr Vice.

Yes I was.
RPS is totally different from a QNH in that it's the lowest FORECAST pressure setting in a particular region rather than an actual measured and reported pressure setting at an airfield or other defined point.

So why not say what you meant, rather than being obscure?

If you've got a point to make, it's helpful to educate people by making it rather than demonstrating some kind of perceived self-superiority.

I'm a strip flier. If I'm staying local I set my altimeter to zero before departure. If I'm not staying local, I set it to field elevation. Should I change my ways before something bad happens?