UK Altimeter Setting Regions vs US single altimeter setting

[Ledhead27]

Something that has been puzzling me for a while, and one that I can't seem to get a definitive answer on.

Within the UK the airspace below the transition altitude is constructed of 21(?) altimeter setting regions, whereas the US uses just a single standard setting of 29.92" Hg across the entire country.

What's the reason behind this, other than the obvious of not having to change the altimeter subscale on a regular basis? Conversely, the profile of the land in USA varies massively, surely it would be better to use several ASRs?

Any help would be much appreciated!

[wiggy]

whereas the US uses just a single standard setting of 29.92" Hg across the entire country.

Always 29.92" (i.e. "standard" ) below transition Level - everywhere in the States ? Wasn't aware of that.... most of the G/A guys I've heard in the States seem to use the altimeter setting appropriate to the facility they are talking to. Be interested in what the non radio guys do.

[sapperkenno]

I don't think they do. I used to set it off the nearest AWOS/ATIS if out in the sticks. Non-radio I'd imagine you could either set airfield elevation before you took off, or found the info from 1-800-WX-BRIEF or one of the other decent weather briefing services you can get out in the US prior to departure.

I wouldn't be so certain everyone in a specific UK ASR is on the same setting... The number of initial calls you hear from people requesting a radar service, and on being asked to pass details your hear all sorts of varying QNH/QFEs reported. Then you might get people transiting a zone, with the airfield QNH set, while they're on a basic/traffic service OCAS (where everyone else is on the RPS), or some even at a flight-level. Then there's the ones not talking, doing whatever they want OCAS.

Never heard this 29.92 all over the place thing though, that's news to me.

[RAT 5]

I think the questioner has got it slightly confused; unless they have changed things in the last 16 years since my last visit. There is a nationwide TA of 18,000'. In EU there are numerous, and some at airfields quite close to each other, but just across an FIR/AIS boundary. Very confusing and perhaps not good in this TEM world. It has been discussed before why UK and/or continental EU does not have a single TA. I do not know the state of that debate.
In the USA, outside Alaska the highest spot is 15,325', according to wikipedia. I assume this was used to decide upon 18,000'. In UK I remember the highest MSA to be 5800'; I stand to be corrected. In Continental Europe, outside eastern Europe, it is 18,600'??
So UK could use a universal 8000' to allow for various weather corrections; or even 10,000'. Continental Europe, using the USA model would go for 20,000'. Both these should allow for pressure & cold weather corrections and be easy to remember.
I wonder if this is what the questioner was alluding to?

An aside: the USA 18,000' has always made me believe why the the Boeing QRH has the Emergency Descent to 10,000' or MSA if higher. It is the correct setting in USA i.e. QNH. In EU controlled airspace 99% of the time you will be above T.LVL and thus every other a/c will be on STD. Will ATC really let you fly around in their airspace on QNH when above TA? I very much doubt it, and stand to be corrected by an ATC-er. Please, please tell us what you would do with an a/c at 10,000' QNH in the Ambers?
Thus, if UK had TA = 10,000 and continental Europe 20,000' then you could descend to 10,000 QNH in all areas, MSA allowing.
By the way; I was severely bollocked, in the sim, for descending FL 80 over UK so not to cause an RA. WRONG according to QRH; but that's for another thread.

[peekay4]

Coming soon to an airspace near you:

EASA/EUROCONTROL Harmonized European Transition Altitude (http://www.eurocontrol.int/articles/harmonised-european-transition-altitude-heta)

[MarkerInbound]

We used to have a higher floor for the Positive Control Airspace in the western part of the US, FL240. It was lowered as part of the fallout from 1956 Grand Canyon midair.


The regs here state you'll set the QNH of a station along the route and within 100 miles or an appropriate station. If you're flying IFR in controlled airspace you'll use whatever setting ATC gives you. I don't know where the OP got the idea we use QNE as QNH. Having seen 28.40 and 31.60 you'd be in a world of hurt stuck on 29.92. There are over 600 chunks of Class B/C/D airspace in the US each with their own altimeter setting so 21, meh.

[ShyTorque]

LFAJ,

I'd say you've got it about right, despite the wine!

As far as RPS in UK is concerned, my understanding is that in years gone by, when local QNH could be quite difficult to come by, it was a way of obtaining a "safe" (i.e. pessimistic) altimeter setting for a long flight out of radio contact. Some aircraft radios had only a limited number of frequencies and needed physical crystal changes by the ground crew in order to obtain others (I trained on some military aircraft that were like this).

These days, if speaking to an ATC unit close by, I always set their QNH, rather than RPS, so that the relative altitude of other traffic can be readily understood. One exception might be where I might have no-one close by to give me a local setting and so use London or Scottish Information, who can always give the RPS.

[On Track]

ShyTorque, is it really possible to do a long flight out of radio contact in Britain? :confused:

[ShyTorque]

Did you not read paragraph two?

[Mach Jump]

Hi Leadhead.

LFAJ, and ShyTorque have it about covered.

...is it really possible to do a long flight out of radio contact in Britain?

I suppose it depends what you call a long flight.

You can fly the entire length of UK airspace direct from Dover, by the English Channel, to the Shetland Islands, in the north of Scotland,(600nm+) at 3,000' without talking to anyone.

In my opinion, the sooner we get rid of the archaic RPS and introduce a common UK/Europe wide TA the better.


MJ:ok:

[On Track]

Obviously there should be a common transition altitude across Britain. I think Rat 5's suggestion makes good sense.

But that's a separate issue from the QNH that you dial up when you are below the transition altitude.

Ledhead, 29.92 inches (1013 hPa) is the setting used everywhere above the transition altitude, not below it.

Mach Jump, I'm surprised you can fly so far in Britain without bumping into controlled airspace somewhere along the way! Does it require lots of twisting and turning?

In Australia you can fly thousands of miles without a clearance, and there are some parts of the country where you can't communicate with a ground station on VHF even if you are at 10,000 feet.

ShyTorque, I interpreted "out of radio contact" as "out of radio range."

[wanabee777]

Remember, as the local atmospheric pressure decreases below standard, the lowest usable FL in that area increases.

CFR 91.121

FAR Part 91 Sec. 91.121 effective as of 09/30/1963 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/0/da37f1d83828491d852566cf00615210!OpenDocument)

ATC often misses this and will clear you to an unusable FL if you're not vigilant.

[Mach Jump]

Mach Jump, I'm surprised you can fly so far in Britain without bumping into controlled airspace somewhere along the way! Does it require lots of twisting and turning?

No. You can fly a straight line (admittedly mostly over the North Sea) between those points.


MJ:ok:

[Ledhead27]

Thanks for the info chaps. Seeming as I've never flown in the United States before it's certainly something that takes a bit of understanding for me, bearing in mind that I'm used to the rather prehistoric QFE antics.

Decided to do a bit of a "googling" and found that the idea of having ASRs is certainly one that wants to be changed, and has been discussed under the Eurocontrol idea (thanks for the link Peekay4). I've done a fair bit of VFR flying around the UK and it certainly is a case, I've found anyway, that the use of the ASR regional pressure is very much hit and miss (i.e nearby airfield QNH may be provided rather than the regional). Also, certainly gives the altimeter subscale a good workout as it's being frequently changed.

[wanabee777]

Maybe I should have been more specific and said U.S. ATC.

[Supermattt]

Hi All,

In the UK, is the current transition level being used by an ATC unit published anywhere (ATIS or METAR say?) or is the minimum separation from transition altitude that an ATC normally uses published anywhere (AIP?)?

Am I right in thinking that when the QNH is above ISA, the lowest usable FL in the UK is normally going to be transition level +499ft?

Cheers
Matt

[Denti]

As far as i know there is a medium term plan to have a unified transition level of 11.000ft all over the EU or something like that. I believe that is the reason why austria changed to that level recently. However, by then the UK will in all likelyhood no longer be a part of the EU and therefore the EU rules will not be applicable anymore.

[Tinribs]

The questioner, and many of the answerers, seem to be confusing different aspects of altimter settings

The UK has regional pressure settings for atimeter settings regions which are the lowest FORCAST pressures for the areas concerned. The object being that if you are unable to contact ground stations or loose contact setting regional pressure settings will give you a safe terrain avoidance. The settings are a relic of the wartime habit of returning bombers to arrive at the wrong location and impact terrain , often just below mountain tops

RPSs are forecast several hours in advance to be noted when flight planning and only used when no better information is available. They are cover large areas, usually several counties, and have easily remembered names eg TYNE

The transition altitude and the pressure to be set above that altitude are entirely different issues. This is the altitude above which a standard pressure setting is to be used. The level is lower in the UK than the states because our terrain is not as high, anywhere. The standard pressure setting is 1013.25 mbs or 29.2 inches. Modern altimeters show both measures on different parts of the dial. The purpose of the standard pressure setting is nothing to do with terrain but avoids collision. If two aircraft are flying with the standard pressure set and maintaining a flight level a thousand feet apart they will not collide, baring gross altimeter error. The dials may not show an accurate distance above the ground but that does not matter the important thing is the aircraft will be separated by a thousand feet.

[Discorde]

The absurdity of UK altimeter setting procedures was examined at length in this thread. (http://www.pprune.org/private-flying/368781-qfe-who-needs-regional-altimeter-setting-ditto.html)

[Meikleour]

Discorde: you are supposed to be on holiday - stop "lurking"!!!

[Discorde]

Hi Mikleour - it was supposed to be a quiet holiday in Orléans. Somehow 'New' also got typed into the nav program & we've ended up in a bustling city on the south coast of a French colony on the other side of the Atlantic where they play 1920s Jazz in all the bars - which is OK. Enjoy your vac in the city of the angels.

[Tinribs]

Dis says our procedures are absurd, this attitude displays ignorance of the long and tortuous process through which they have developed and the blood spilt in the process
UK is odd in having steepish slopes near cities and high ground nearby
Often runways are aligned so that approaching aircraft miss the terrain though incurring a crosswind on most days to do so, study the Glasgow plate
On a further note , if a seemingly sane group of people do something you don't understand, they could be stupid or perhaps you don't understand

[Discorde]

The current procedures were introduced when QNH info was not readily available and many aircraft flew non-radio, which is not the case nowadays.

The low UK transition altitude was set when airliner rates of climb were considerably lower than today's equivalents. The current combination of low TA and high initial ROCs is a potential cause of level busts.

Most countries do not use QFE.

[peekay4]

UK is odd in having steepish slopes near cities and high ground nearby
That's not at all unique.

[oggers]

...quite. In anycase when someone tells you 29.2 is the SPS (which isn't a typo because he's already been back and edited the post) you know they are talking cobblers.

[5milesbaby]

It has been mentioned in the original post and also since resurrection that Europe will be harmonising the TA. The project has been shelved and all work done in the UK has been archived probably to never see daylight again.