QNH or QFE ?

[double_barrel]

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

[Discorde]

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

[Fl1ingfrog]

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.

[xrayalpha]

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.

[double_barrel]

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

[Jan Olieslagers]

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.

[India Four Two]

“Altimeter setting” or just “Altimeter” is universally used in the US and Canada. Most pilots here have never heard the term QNH or any other of the Q codes.

[MarkerInbound]

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!
.

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.

[double_barrel]

...... I heard one Captain had converted a power drill to set the altimeter going into Mexico City.

Spluttered my coffee onto keyboard.....

[Pontius]

“Altimeter setting” or just “Altimeter” is universally used in the US and Canada. Most pilots who are too lazy to read the AIM here have never heard the term QNH or any other of the Q codes Adjusted at no cost :ok:

Russia, China and some of the -stans still use QFE. China uses QNH (in Hectopascals).

I heard one Captain had converted a power drill to set the altimeter going into Mexico City. That's funny :}

[Thud105]

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

[Discorde]

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

QFE who needs it? (https://www.pprune.org/private-flying/368781-qfe-who-needs-regional-altimeter-setting-ditto.html)

[BackPacker]

“Altimeter setting” or just “Altimeter” is universally used in the US and Canada.

"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.

[Discorde]

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.'

[spekesoftly]

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"

[India Four Two]

It would be helpful if the US adopted hPa ...

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

[2 sheds]

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.

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

2 s

[BackPacker]

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

[MarkerInbound]

China uses QNH (in Hectopascals).



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.

[BossEyed]

I heard one Captain had converted a power drill to set the altimeter going into Mexico City.

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

[MarkerInbound]

I flew some second hand AA 727s. Their altimeters had an expanded range for the Kollsmam window. It's all what you're willing to pay.

[beamer]

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.

[scifi]

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.
.

[chevvron]

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.

[Discorde]

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.

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.

[Dave Gittins]

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

[TheOddOne]

Denham circuit height 750 ft elevation 249ft.
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

[chevvron]

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

QFE who needs it? (https://www.pprune.org/private-flying/368781-qfe-who-needs-regional-altimeter-setting-ditto.html)
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.

[Discorde]

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?

[chevvron]

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?

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.

[Meikleour]

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

[Jan Olieslagers]

@Discorde: thanks for the copy!

Regarding A simpler procedure would be to set local QNH for the whole flight, resetting only if the QNH changes : 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.

[chevvron]

@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.

[Jan Olieslagers]

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.

[Maoraigh1]

"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?

[Mr. Vice]

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.

[chevvron]

I suspect chevvron may be alluding to the fact that it is correctly called the Regional Pressure Setting.

I'm all for getting something technical correct where it matters, but pedantry for the sake of it does become a wee bit wearing! :rolleyes:
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.

[eckhard]

And useless for most pilots as a result.

[hoodie]

Yes I was.

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.

[Flyingmac]

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?

[BackPacker]

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.

And useless for most pilots as a result.

I don't agree. We measure altitude (or height) in an aircraft not just so that we can impress our passengers about how high we actually are - although from the PA announcements in a commercial airliner you might think that that is still the case.

We measure altitude or height for at least three specific purposes:
1. To measure how high we are above an airfield or runway. This is important for circuit altitude/height, and for IFR procedures to determine when to go around or land (DA, MDA).
2. To measure how high we are related to surrounding terrain, and to achieve whatever obstacle clearance we think is necessary.
3. To have a common datum when aircraft are reporting altitude, so that two aircraft that are reported to be in the same position, but at a different altitude, are indeed a certain amount of feet apart. In other words, for collision avoidance.

RPS is useless for 1, as it is not sufficiently accurate. But it is perfectly usable for 2 and 3.

[chevvron]

One problem with using RPS in the UK is when flying below a CTA where the base is notified as an altitude; the RPS can be low enough to cause the pilot to infringe if they try to fly just below the CTA.
I once watched a stream of Hercules not talking to Farnborough or Gatwick crossing MID VOR south eastbound all indicating 2,700ft where the base is 2,500ft (this was in the days before the RAF recognised the 'rule' about using an actual QNH when flying below a TMA) because they were using the Chatham RPS. Particularly annoying for Gatwick as they were landlng on easterlies at the time.

[Discorde]

Not too long from now all primary altimetry will be GPS derived and barometric altimeter setting will be retained purely as back-up. On commercial aircraft local QNH will be auto-uploaded by data link and inputted to back-up barometric altimeters, both to confirm GPS altitude and to give redundancy. For GA pilots the option will be available to adjust indicated altitude to height for local flying.

It could be that the term 'flight level' is retained, meaning - as now - altimeter indication (in feet) divided by 100 and the word 'feet' will become redundant, removing the complications of parallel Imperial/metric systems. Perhaps for low viz ops decimal FLs for Decision Altitudes could be specified.

[BackPacker]

One problem with using RPS in the UK is when flying below a CTA where the base is notified as an altitude; the RPS can be low enough to cause the pilot to infringe if they try to fly just below the CTA.
I once watched a stream of Hercules not talking to Farnborough or Gatwick crossing MID VOR south eastbound all indicating 2,700ft where the base is 2,500ft (this was in the days before the RAF recognised the 'rule' about using an actual QNH when flying below a TMA) because they were using the Chatham RPS. Particularly annoying for Gatwick as they were landlng on easterlies at the time.

Good point. More in general, we all tend to report a number which we think is our altitude (or height), but omit to include the information how that altitude or height was derived. Heck, we even omit the word "height" or "altitude" on most occasions.

I was doing my IMC rating at Leicester (almost 500' elevation), when QFE was still used a lot for VFR flying. So I was entering the practice hold (situated more or less overhead) at 2000' on the QNH (and reporting "holding at 2000") while other aircraft were doing VFR overhead joins at 1500' on the QFE (and reporting "overhead join at 1500"). It did not take very long to realise that we were actually just feet apart. From that moment on I started reporting my altitude as "2000 feet on the QNH, 1500 feet on the QFE".

Mixing two altimeter datums in the same airspace is dangerous. For safety, all aircraft in the same airspace should use the same datum. Whatever that datum is, I don't care, as long as everybody knows and uses it.

[BackPacker]

Not too long from now all primary altimetry will be GPS derived and barometric altimeter setting will be retained purely as back-up. On commercial aircraft local QNH will be auto-uploaded by data link and inputted to back-up barometric altimeters, both to confirm GPS altitude and to give redundancy. For GA pilots the option will be available to adjust indicated altitude to height for local flying.

I don't think so. Not because it's not possible, but because there needs to be a transition period to get from one system to the other. And during that transition period, some aircraft will base their altitude measurement on a GPS reading, and others on a barometric reading. However, there is no way to convert an accurate barometric-based altitude reading into the equivalent GPS-based altitude reading and vice versa unless you know not only the local QNH, but also the exact environmental lapse rate at your given position. Heck, you even need to know the actual humidity across the whole column of air below you. Using the standard ISA lapse rate for this instead may lead to hundreds of feet of error if you're flying at FL300. That's a whole order of magnitude worse than the normal accuracy of analog, mechanical barometric altimeters, and even more orders of magnitude worse than GPS-derived altitude. So during the transition period we would need to use significantly more separation than what's applied now. While the current trend is to reduce separation (RVSM) to improve airspace capacity. I don't think that would work.

Even transitioning from 25 kHz-spaced VHF frequencies to 8.33 kHz spacing will eventually take something like 10 years. And that's a transition that's backwards compatible (8.33 kHz radios can be used in 25 kHz airspace).

[Discorde]

However, there is no way to convert an accurate barometric-based altitude reading into the equivalent GPS-based altitude reading and vice versa unless you know not only the local QNH, but also the exact environmental lapse rate at your given position. Heck, you even need to know the actual humidity across the whole column of air below you. Using the standard ISA lapse rate for this instead may lead to hundreds of feet of error if you're flying at FL300.

Adjusting GPS altitude to match indicated barometric altitude would be accomplished electronically within the apparatus without pilot input required.

[chevvron]

Adjusting GPS altitude to match indicated barometric altitude would be accomplished electronically within the apparatus without pilot input required.
And just how long and how much money would it take for the CAA to certify and approve such an electronic system?
You can go to a shop today and buy a Casio wristwatch which will display your altitude, but I don't think the CAA would accept that in lieu of a barometric altimeter.

[BackPacker]

Adjusting GPS altitude to match indicated barometric altitude would be accomplished electronically within the apparatus without pilot input required.
And where would this gadget get its input data from? As I said, the gadget needs the local QNH and the actual local environmental lapse rate (+humidity) of the whole column of air below you, to do the calculation. Otherwise your electronic gadget is just going to be a GIGO system (Garbage In - Garbage Out).

[BossEyed]

As I said, the gadget needs the local QNH

And if you need and therefore have got that, why not just display it?

Electronics are not inherently better; sometimes simple is the way to go, using the environment rather than man-made infrastructure.

[Discorde]

And where would this gadget get its input data from?

From the aircraft's static ports.

The point about GPS derived altimetry is that it removes the need for altimeter setting, with its attendant drawbacks. Every time a subscale setting change is required there is the risk of mis-setting or omission of resetting. In European airspace, with low transition altitudes, the authorities are obliged to publish notams every time a deep low pressure weather system passes through, warning pilots about the dangers arising from failure to reset when there are large QNH/1013 differences.

The transition process will be similar to the gradual adoption of RVSM and RNAV approaches, with the procedures introduced initially into low traffic density airspace to prove efficacy.

[Maoraigh1]

Flying vfr east east from Inverness, I'm passed to Lossie Radar (Air Force) who tell me to fly on Lossie QFE ###. I'm remaining outside the MATZ, but in the Area of Intense Airial Activity.

[scifi]

Quote... 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?
Really you should not twiddle with the knob on the front of the altimeter, the manufacturer will have set it correctly, and it should not be altered, unless you are an Instrument Technician.
Also there is no real good reason to report your altitude to ATC, as they have your Transponder reading on their displays, and their system will alert them of any clashes.
.
Problem solved....

[Il Duce]

scifi
Assuming you have a transponder with Mode C which is within tolerance. ATC won't know if it's within tolerance unless you speak to them and they verify your altitude; then "problem solved".

[chevvron]

Quote... 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?
Really you should not twiddle with the knob on the front of the altimeter, the manufacturer will have set it correctly, and it should not be altered, unless you are an Instrument Technician.
Also there is no real good reason to report your altitude to ATC, as they have your Transponder reading on their displays, and their system will alert them of any clashes.
.
Problem solved....
If ATC identify you using SSR, they have to validate any Mode C reading associated with your transponder code which requires you to report what you are seeing on your altimeter.

[Jan Olieslagers]

In which case one pushes the appropriate button on the transponder, and reports what the display shows... Problem solved, indeed.

[chevvron]

In which case one pushes the appropriate button on the transponder, and reports what the display shows... Problem solved, indeed.
No.
The altitude encoder transmits a reading based on 1013.2 hpa which is then converted by the radar display on the ground which has the current QNH fed into it and updated when necessary.

[Silvaire1]

As an ex-controller who used to work terminal areas, having more than one level datum was just day-to-day business. Aircraft coming into my area of responsibility were often at or descending to a FL, below TA QNH was the common pressure setting used and around the aerodromes QFE might well have been used. Include in the mix aircraft transiting the control area which might have been on the Regional Pressure setting, with the added bonus that being close to the boundary between two Altimeter Setting Regions, the RPS might have been different depending on whether the aircraft was coming from the North or South.

The rules of the game were to separate aircraft that needed separating and give traffic info on those which didn't. For separation there was a simpler system that displayed what FLs were separated from aircraft below TA and for traffic info, levels rounded to the nearest hundred feet were easy to work out (and if they were VFR and not going to be in my airspace for long I saw no reason to get all aircraft to change to one of the aerodrome QNHs). I don't dispute that more than one pressure datum means that there is more to think about, but it concerns me to think that there may be pilots or controllers who have trouble with simple altimetry calculations when values rounded to the nearest hundred feet will suffice for most purposes.

That is amazing. I'm genuinely glad none of the controllers I deal with are faced with that game, given my base in one of world's densest packed terminal areas (and all traffic on the same altimeter setting). The situation described in one of those classic British situations where a totally inefficient non-system is made to work through the application of skill... and those concerned think it is normal!

[chevvron]

No.
The altitude encoder transmits a reading based on 1013.2 hpa which is then converted by the radar display on the ground which has the current QNH fed into it and updated when necessary.
It is a requirement that the controller MUST cross check what you see on your altimeter with what is displayed on the SSR label; a +/- 200ft difference is allowed.

[Whopity]

Q-Codes;- a brilliant, ground-breaking idea - in 1909. Possibly not that relevant, or even useful, more than a century later? Discuss.
QFE? Ridiculous.
It is interesting to note in the 1949 Air Ministry book of Q Codes that QNH did not exist at that time! The two pressures used were QFE, surface pressure at an aerodrome and QFF, pressure at mean sea level. QNH first appeared in the eraly 1950s following an amendment to the method of determing the Sea Level Pressure when not at sea level.

[powtough]

That would require changing a lot of altimeters - over 200,000. It's not going to happen.
Is it true that western altimeters don’t have index mark which you set to barometric (pressure altitude) of runway airfield, so that on touchdown you read 0 height (QFE), especially in mountainous areas.

[A and C]

The last bastion of QFE is the RAF , this is largely because it helps those flying a high workload fast jet that has minimal navigation kit recover using PAR ( usually with less than ten minutes fuel remaining) Did not need another thing to think about so having the runway at zero on the altimeter was a good idea.

Things have moved on and the fast jets carry far more navigation kit now so recovering aircraft in IMC is much less fraught so once the “When I was on Lightning’s” brigade has retired you can expect a change to a more international way of doing things.

I expect QFE to continue in UK flying clubs for some time as most of them still teach ancient techniques such as Gypsy style engine management when For the last forty years they have been operating Lycomings.

[Meikleour]

Discorde: Until you can persuade flying schools to stop teaching QFE procedures then nothing will change! I have even noticed going into my nearest busy GA field that the A/G operators will refuse to give QNH to arrivals even when requested - only give it for departures!! Go figure.

[BDAttitude]

Is it true that western altimeters don’t have index mark which you set to barometric (pressure altitude) of runway airfield, so that on touchdown you read 0 height (QFE), especially in mountainous areas.
You might very soon run out of scale. The one I'm using most has 940hPa as smallest value.

[Jan Olieslagers]

I have even noticed going into my nearest busy GA field that the A/G operators will refuse to give QNH to arrivals even when requested Might well be the same level of "intelligencies" that voted "pro" Br_x_t.

(and by the way, thanks for correctly naming A/G operators - there are those who want to call them controllers, even if they do not control any airspace)

[ETOPS]

My home airfield is 73ft AMSL thus only 2mb difference - an easy bit of maths if only QFE offered.

[chevvron]

Discorde: Until you can persuade flying schools to stop teaching QFE procedures then nothing will change! I have even noticed going into my nearest busy GA field that the A/G operators will refuse to give QNH to arrivals even when requested - only give it for departures!! Go figure.
ATC, AFIS and A/G should all pass QNH as standard with QFE available only on request according to CAA guidance issued about 15 years ago.

[Meikleour]

ATC, AFIS and A/G should all pass QNH as standard with QFE available only on request according to CAA guidance issued about 15 years ago.
chevvron: thanks for that info - good luck with pointing that out to Headcorn A/G!

[Dave Gittins]

I sometimes fly in Colorado and with the airfield elevation at 6870 ft there is no way you'll use QFE.

[chevvron]

chevvron: thanks for that info - good luck with pointing that out to Headcorn A/G!
Presumably you read my bit about Headcorn on the 'other' forum, but I'm told the A/G operator when that occured has left there now.

[jmmoric]

Since the last part of flying is done visually, is it really that relevant having your altimeter show 0 when landing at all? Once you pass the DH or DA you look out the windows anyway... or am I doing something wrong here?

[Jim59]

I guess that most of the anti-QFE contributors don't have display authorisations. The vertical limits are all expressed in heights in "CAP 1724 Display Standards Document". Converting altitudes to heights several times in an aerobatic figure is probably not good for a display pilot's health. Yes, the need to set QFE is not necessary for most regions of flight - but for some activities it makes more sense than QNH. I'm sure contributors can find other examples where QFE is the safest option. Not all flights are take off - cruise - land.

[Fl1ingfrog]

This argument has gone on for as long as I can remember. to the extent its almost pointless. I would hope that anyone performing low level aerobatics will have it firmly implanted in their minds the altitudes or heights that must be achieved both at the top and at the bottom of a manoeuvre. The QNH pilot listens in a wonder of disbelief that anyone would mess around with the altimeter at critical moments (resetting to QFE). Knowing the elevations is part of everyday flying for QNH pilots. The only rule that I demand is that you fly one or the other and then use it at all times, but never mix it. If an a/g operator refuses to pass the QFE or other wise QNH ( a FISO or ATC will never refuse) this will require a very stern chat with the fool after landing such that he/she will never refuse to do so again.

In the majority of countries throughout the world QNH is the norm.

[460]

I was born and bred with QFE & used QFE for 33 years of RAF flying.
I much prefer QNH.
(& in my glider always have height + altitude + FL all on display in front of me; modern electronics)

[India Four Two]

In the USA (and other countries) how do pilots performing aerobatic displays above high-elevation airfields set their altimeters?

Discorde,

The same way as everyone else - they use the current Altimeter Setting (QNH* to you) and then convert all their gate heights to the appropriate altitude.

Of course, sometimes pilots get it wrong:


https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/630x895/fbc51116_6b0f_466d_a1da_fb945644b656_aec9cdf9c0fe1b581c6af80 9ce6b07b598fbff4c.jpeg

https://m.youtube.com/watch?v=alo_XWCqNUQ

Just out of interest, I checked the Winter altimeters in my club’s two-week old ASK21B. With the field elevation of 3700’ set, the sub-scale read 1020 mb. I then made 43 twists of the knob to bring the altitude to 0’ and the sub-scale read 997 mb. I was surprised I was able to do this. Last time I tried this many years ago on an old US altimeter, I ran out of sub-scale.

The observant will notice I used mb rather than inches. This is because our glider was delivered with European altimeters! We shall be having words with the factory!

Using the Altimeter Setting doesn’t seem to cause any problem for new pilots. Our students have no difficulty figuring out that the downwind leg starts at 4500’ (800’ AGL).

* I would guess that 99% of North American light plane pilots would have no idea what QNH, QFE or any of the Q codes are.

[jmmoric]

The observant will notice I used mb rather than inches. This is because our glider was delivered with European altimeters! We shall be having words with the factory!

Those damn europeans!

On a side note, when I flew glider, we had a polish model, and the altimeter was in metres.... which is probably "meters" now that the UK has left the EU.

[oggers]

The QNH pilot listens in a wonder of disbelief that anyone would mess around with the altimeter at critical moments (resetting to QFE). Knowing the elevations is part of everyday flying for QNH pilots. The only rule that I demand is that you fly one or the other and then use it at all times, but never mix it.

What is the "QNH pilot"? Is that someone who never flies above transition altitude?

[double_barrel]

The only rule that I demand is that you fly one or the other and then use it at all times, but never mix it.


Since this thread seems to have risen from the dead, may I ask what altimeter settings do people who fly glass cockpits with a standby steam gauge use on each? I flew with someone recently who kept QNH on the G1000 but 1013 HPa on the standby dial. I don't really see the logic of that, is there a 'best practice' for this situation?

[jmmoric]

Since this thread seems to have risen from the dead, may I ask what altimeter settings do people who fly glass cockpits with a standby steam gauge use on each? I flew with someone recently who kept QNH on the G1000 but 1013 HPa on the standby dial. I don't really see the logic of that, is there a 'best practice' for this situation?

Doesn't make sense, since the standby is a standby, and you should be able to check towards it to spot malfunction?

But I guess the more professional know the answer better than I..

[Meikleour]

India Four Two: are you sure the lower setting was 997 mb. since 23 mb. Difference does not equate to 3,700 ft?

[Fl1ingfrog]

There are some justifiable reasons for setting standard pressure on the second altimeter: should your flight altitude be close to the base of an airway/controlled airspace, which is designated as a flight level, because it could act as a valuable heads up. Similarly when flying using regional pressure (UK) then having the aerodrome QNH set on the second altimeter does a similar job when flying below the base of controlled airspace which is designated as an altitude. For those who land using QFE then having the aerodrome QNH set on the second altimeter is a common practice, ready for a go around and diversion.

But, once again we return to the possible folly, in the minds of QNH people, of fiddling about with altimeters at a critical point in the flight. QNH, QNH and only QNH is the normal standard of IFR pilots and also for those who regularly fly internationally. Outside of the UK and France QFE is rarely found. It was a common practice for commercial transport flights to land at one place using QNH and another using QFE, whatever was provided locally. This could happen many times on the same day and was a recipe for disaster. I can remember a number of tragedies with a considerable loss of life owing to the miss-setting of the altimeter by the pilots during the approach to land.

[chevvron]

The observant will notice I used mb rather than inches. This is because our glider was delivered with European altimeters! We shall be having words with the factory!

Is that a bit like hectopascals?Devil

[Jan Olieslagers]

Is that a bit like hectopascals?Devil
Yes, quite a big bit like actually.Angel

[MarcK]

On a side note, when I flew glider, we had a polish model, and the altimeter was in metres.... which is probably "meters" now that the UK has left the EU.
https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/1000x645/feet_to_meters_bkliban001_eeeb0757cbf0683a7b285c33d439cf9697 ce6f34.jpg

[golfbananajam]

chevvron: thanks for that info - good luck with pointing that out to Headcorn A/G!


Not according to CAP413:
section 39 "All messages relating to an aircraft’s climb or descent to a HEIGHT or ALTITUDE employ the word ‘to’ followed immediately by the word HEIGHT or ALTITUDE. Furthermore, the initial message in any such RTF exchange will also include the appropriate QFE or QNH" which gives the example "G-CD, descend to height 1000 feet QFE 997 hectopascals".
or section 4.43, 4.44, 4,64, 4.84 and many others too.

[India Four Two]

India Four Two: are you sure the lower setting was 997 mb.

I did wonder about that but here's what I saw:


https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/2000x1504/altimeter_0_img_7330_ddfc91e12eef094e3f05f3904a857f9932dd9dd 8.jpg

After allowing for the fact that I misread the sub scale (!), 992.6 is still not right.
I went back to the hangar today and paid more attention during winding back. I was seeing about 30' per mb - HPa - sorry chevvron! - which is what I expected and then I noticed this at 1800':

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1309x1187/altimeter_1800_img_7348_a5813063b40e71e1a229baec63692279867b 305e.jpg

The sub scale ends at 945 HPa, but you can still wind back onto the sub scale for a second time around!

[Meikleour]

golfbananjam: My comment was relating to the practice of some A/G operators who are not empowered to issue air traffic control instructions and not ATC who can!

[On Track]

As I sit here in lockdown and under curfew, and wonder whether life will ever be the same again, this thread surfaces again to reassure me that some things never change.

I still shake my head in wonderment and try to figure out why Brits always want to make things so complicated, when it can all be so simple.

[Prop swinger]

Anyone who finds QFE complicated shouldn't be allowed to fly an aircraft. It's an option that is available to me, when appropriate I will use it. The fact that you don't want to, can't or find it too "complicated" is irrelevant to me. Nor do I feel the need to go onto the internet & demand that everyone should be just like me & do everything the way that I do it because I think that I'm so perfect.

When I tug gliders, I write down the release height for charging purposes. Leaving the altimeter on QFE makes that simpler & since I'm taking off & landing multiple times at the same airfield there's no need to change altimeter settings. Ditto today when I will be instructing in gliders. Since we won't be going anywhere we will leave the altimeter on QFE, although I will be showing students how to set QNH on an electronic display just to show how to use the instrument.

[On Track]

I don't find QFE complicated. Actually I've never used it because (a) it's not necessary and (b) it's not available in any of the jurisdictions where I have flown, but I'm sure I could deal with it satisfactorily if I had to.

But why have two systems operating when you only need one? The rest of the world has already figured out that there are some safety considerations here, and that's why they use QNH exclusively below the transition altitude.

And by the way, if you can't fly a circuit on QNH you shouldn't have a licence. I learnt to fly at an airport where the circuit altitude was 2900 feet (airport elevation 1888 feet).

[Prop swinger]

But why have two systems operating when you only need one? The rest of the world has already figured out that there are some safety considerations here, and that's why they use QNH exclusively below the transition altitude.
Because sometimes it's more convenient. If you feel it's unsafe, don't do it. I'll use QNH when appropriate, usually when flying cross country or landing at another airfield, & QFE if staying local.

This isn't about whether people should use one or the other, it's about the utter boring-ness of people telling other people how they should fly, the obsession with uniformity & conformity by people who cannot conceive that someone else should do something differently.

[oggers]

On Track:


The rest of the world has already figured out that there are some safety considerations here, and that's why they use QNH exclusively below the transition altitude.

You've gone off track there. I understand that in China and most of the former USSR, QFE is widespread. If they ever standardise on QNH at their international airports (which would be a good thing imo) they will be a long way behind the UK.

I was trained to use QFE in the navy. It made perfect sense, particularly to single pilot IF recoveries. It did not complicate things, it simplified them. That was the point. There are plenty of different practices around the world, much of it totally arbitary. QFE is not arbitary, it does not exist simply because 'brits like to complicate things' or 'that's the way we've always done it'. It is a rational option in the specific circumstances where simply knowing your height above the touchdown zone has value in itself. Nobody is advocating using QFE in the cruise instead of QNH. I find it strange that so many people object to the use of QFE. Live and let live.

[cats_five]

As a glider pilot I was taught to fly my circuit without reference to the altimeter. It's an essential skill so as to make a safe landing in field higher or lower than the 'home' field

[On Track]

Prop swinger, it's not a question of choice. The law requires me and everyone else to fly on QNH below the transition altitude (which is 10,000 feet across the whole country). The safety benefits for aircraft separation, when everyone is using a common datum in both controlled and uncontrolled airspace, should be obvious.

[double_barrel]

Prop swinger, it's not a question of choice. The law requires me and everyone else to fly on QNH below the transition altitude (which is 10,000 feet across the whole country). The safety benefits for aircraft separation, when everyone is using a common datum in both controlled and uncontrolled airspace, should be obvious.

That seems very sensible. Now, if only you used HPa rather than furlongs of ale or however you guys measure pressure, that would be the perfect arrangement :)

[Andy H]

Some of us use QFE and some use QNH, we are adults and we use what is most appropriate for the situation we find ourselves in. I do get rather annoyed at people who try to make me do things their way because they think they are right. You do it your way and stop trying to make me fly in an unsafe way, cos I won't listen to you !

[Prop swinger]

Prop swinger, it's not a question of choice. The law requires me and everyone else to fly on QNH below the transition altitude (which is 10,000 feet across the whole country). The safety benefits for aircraft separation, when everyone is using a common datum in both controlled and uncontrolled airspace, should be obvious.That's not the law over here, I have choices and will use them where suitable.

Standardised altimeter settings only makes sense when combined with the semi-circular for cruising flight. When I'm using QFE I won't be in level flight so cruising levels & the associated common datum don't apply.

[Big Pistons Forever]

UK aviation, history unimpeded by progress......

[Piper.Classique]

i once bought a glider that had an altimeter calibrated in mm of mercury. Good luck getting that one from ATC. I flew with it for years, being too mean to change it. i made a little conversion chart that I don't think i ever used. Just left it on 789. I didn't have a radio, anyway '

[TheOddOne]

My favourite aviation joke..

'London, 'Merican 99'

'American Niner Niner, London, descend to altitude six tousand feet, QNH Wun Zero Zero Tree'

'Merican 99, can we have that in inches?'

Certainly, American Niner Niner, descend to altitude seven two tousand inches, QNH Wun Zero Zero Tree'

Hat, coat.

TOO

[Jan Olieslagers]

descend to altitude seven two tousand inches An old one, but it doesn't loose value over the years. Thanks for bringing back the smile!