Is there such a thing as "Regional QNH"?

[GoneWest]

Instructor chappies - and chappesses....I got into a conversation recently with a guy who tells me that there is no such thing as a "Regional QNH".

I was convinced that when I used to operate in the UK there was a deal where the UK was split into numerous "regions" for altimeter setting....and it was called a regional QNH.

Any comments - is there a "Regional QNH" in the UK?

[Kermit 180]

I would think regional QNH zones would be standard to cater for aircraft on cross country flights.

[A and C]

The UK is indeed split into 20 regions for altimeter seting.
A map of these can be found in the UK air pilot or the jepp bottlang airfield manual page UK 4-32.

[RVR800]

In the UK there is; but you're in Florida right?

The US use 'Alimeter' (inches not mBar) for the airport or center they are working and this also shows altitude like QNH (mBar)

[ 04 October 2001: Message edited by: RVR800 ]

[Noggin]

QNH is the pressure at a Point on the Earths surface reduced to mean sea level.

A Regional pressure is the lowest forecast pressure in a defined area for one hour.

Quite right there is no such thing as a Regional QNH.

[bookworm]

The AIP (http://www.ais.org.uk/uk_aip/pdf/enr/20107.pdf) refers to them as Regional Pressure Settings, but the copy of CAP413 on RT phraseology on my shelf (albeit a fairly old one from about 1990) uses the expression Regional QNH. ATC at my home base still refers to the Chatham QNH. So I think your recollection is mostly correct!

[GoneWest]

And the first prize is issued to Noggin.

I have to admit that I made a total b***s of the question - but it was a teaser as I knew the answer to be exactly as Noggin says (at least I knew it after the conversation in question..I genuinely did think it was a "regional QNH").

Now that we have the dictionary definition of the "regional pressure setting", I'd be curious to hear of any written references to "regional QNH" (like in the CAA PPL Navigation written examination papers).

[rolling circle]

It is actually slightly more confusing than Noggin would have you believe. The Regional Pressure Setting is, in fact the lowest forecast QNH (Observed pressure reduced to sea level using the International Standard Atmosphere) in a particular Altimeter Setting Region. The forecast is made 1 hour ahead and is valid for 1 hour (e.g. the forecast for 1200-1300 is made at 1100).

The fact that the RPS is based on the lowest forecast QNH probably accounts for the misquoted 'Regional QNH'. As to why the incorrect terminology appears in licence examinations - best ask the supposed experts at the CAA who set the exams!

[bookworm]

GoneWest

You don't have to look far:

"Plan your circuit using the best
QNH, for example a nearby aerodrome
or failing that the most recent
regional QNH. "

from CAA Safety sense leaflet 12 section 5f

I really don't see what the big issue is. The phrase Regional QNH offers little scope for ambiguity (it's a QNH-like value), unlike Regional Pressure Setting which doesn't tell you much about the datum you're setting.

US forecasters don't seem to have any qualms about using QNH to refer to a forecast value:

EGUL COR 051111 16012G18KT 9999 FEW022 SCT090 SCT130 BKN200 510005 QNH2965INS T19/13Z T12/04Z BECMG 1718 15010G15KT ...(remainder of long TAF snipped)

That might well be WMO-standard.

[BlueLine]

CAP413 is due to be amended to reflect Regional Pressure Settings rather than Regional QNHs which are considered to be an incorrect description.

New edition is usually out in the New Year

[YouNeverStopLearning]

To answer the question that was posed.

Yes there are still pressure setting regions.

Sometimes the value is called the Regional Pressure Setting and sometimes it is called the Regional QNH.

Very often the RT phraseology is expressed differently to other references for the same thing in order to reduce RT clutter. For example, when requesting the Regional in the air "... Request Chatham QNH ..." is shorter than "... Request Chatham regional pressure setting ..." and hence reduces RT transmission time!

It's as simple as that. ;)

[rolling circle]

And how much shorter is 'Chatham QNH' than 'Chatham RPS' (or Chatham Regional)?

Let's face it, practical RTF has little to do with the esoterics of QNH versus RPS. Those who use the radio are all human (even the air trafficers) and will use whatever phraseology suits them, no matter what appears in CAP413, ICAO Annexes or any other publication that nobody ever reads.

The original question was "Is there such a thing as Regional QNH?". The pedantically correct answer is 'No, there isn't'. But who the hell cares?

In the current climate, don't we all have far more important things to think about?

[GoneWest]

<<In the current climate, don't we all have far more important things to think about? >>

So why have you bothered to post two messages about it?? (teasing!! :D )

[GoneWest]

The more I think about it - I wonder if I am teasing.

Who cares - presumably not Rolling Circle (who will probably read this thread three times now - even though he knows its contents)...maybe students and instructors care.

Students might care because they have the ability to fail written examinations, which - certainly in the case of R/T - are often based on pedantics.

Instructors might care because they care what they are teaching - and want their students to get it right....especially when they come o do their written examinations.

Do we "care" about the definition of "Roger"? Does it matter whether we use the phrase to say "I have received all of your last transmission" or to say "I have received and understood all of your last transmission"...again, it's failable when it comes to exam time.

Or - could it be that the current thinking in the aviation industry is along the lines of "not caring" about standards.

<<edit for typo>>

[ 06 October 2001: Message edited by: GoneWest ]

[Whirlybird]

Interesting thread. Maybe not of tremendously earth-shattering importance, but interesting just the same. If you don't like it, don't read it. But I learned something from it, so thanks everyone.

[Lima Xray]

Be aware that when you fly just under say the London TMA you may infringe the protected airspace by flying on the regional pressure setting. In that case check against A/P QNH with ATC or ATIS.

[GoneWest]

Whilst what you say is correct - is it not a point of Air Law that when operating below such airspace, you should have the relevant aerodrome QNH set in the window??

You shouldn't be operating on a regional pressure when under the "TMA" - in a single altimeter aircraft, that is.

[BAE employee]

The question was "are there regional QNHs?" - the answer is a simple "in the UK at least, yes".

However, unless you are flying a VFR nav at a particular altitude outside of controlled airspace then they have very little relevance to anyone. If you are VFR, any "altitude" info is purely for information, as you should get a "proper" QNH/QFE when you arrive at your destination airport.

If you are flying close enough to an airport that you need an accurate QNH, then in all honesty the ATIS will give something that is much more relevant.

In anycase, the variation in QNH over a region that covers about 5% of UK airspace isd likely to be pretty small. Also, a great deal of the traffic around is above the trans alt anyway (maybe you should aim to fly above the trans alt on 1013? Would that be a safer bet as everyone else up there is on the same setting?).

I can't remember what they do in the USA and Canada because of the 18,000' blanket trans alt - could someone remind me (it is 10 years since I last went there). i would have though that a regional QNH/RPS had more relevance there than in the UK.

[Noggin]

The term "Regional QNH" whilst used frequently in UK is incorrect. QNH is measured at a point. A point cannot be "regional". The correct term is "Regional Pressure"

[Kirstey]

But Reigonal QNH is not measured at a point. It is a forecast for a region, and within that reigon for that hour the QNH will not fall below that level. It's an lowest case scenario.

or am i talking pants?

[moggie]

Kirstey - your pants are well in order and are not talking for you. The RPS is the lowest forecast "QNH" for the WHOLE region and as such covers all those points that are normally used to measure the QNH.

It is a forecast, not a measurement, and so does not need to be "taken at a point" as the actual QNHs may not even get that low - it is just the most pesimistic guess (sorry, estimate) that the met man can come up with.

[Noggin]

Kirstey,

Because it is not measured at a point, it does not fit the definition of a QNH which is defined as follows:

The pressure setting which causes the altimeter to read the height above mean sea level of the touchdown on landing, plus the height of the altimeter above the ground.

QFF is the barometric pressure at a stated place, reduced to mean sea level.

A Regional Pressure setting is a QFF not a QNH.

MET.O 630/AP3340 Capt 9.

[ 09 November 2001: Message edited by: Noggin ]

[moggie]

we seem to have an outbreak of pedantic semantics. Technically the RPS is NOT a QNH, in practice it is! It functions like a QNH, it reads a (pessimistic) altitude AMSL and will help you to avoid a) the ground, b) aeroplanes, c) controlled airspace.

OK, it is a forecast regional pressure (not a measured pressure) but still works the same.

[Noggin]

and will help you to avoid ................ c) controlled airspace

Unfortunately it has quite the reverse effect. There is no controlled airspace anywhere defined on the basis of regional pressure. More people infringe controlled airspace with this ridiculous setting by flying higher than they think they are.

[rolling circle]

Oh dear....

QNH - The observed pressure at a station, reduced to sea level using the International Standard Atmosphere

QFF - The observed pressure at a station, reduced to sea level using actual atmospheric conditions

Regional Pressure Setting - The lowest forecast QNH within a defined area, valid for one hour and forecast one hour in advance.

Source: Forecasters Course Notes, Shinfield 1976.

Since both QNH and QFF depend upon observed pressure and RPS does not, it is clear that 'Regional QNH' is a misnomer and, therefore, that there is, strictly speaking, no such thing as Regional QNH.

However, it really doesn't matter whether you call it RPS, Regional QNH, FOQNH or Joe Bloggs - it all means the same thing, so what's all the fuss about?

Which seemed to annoy GoneWest, for some strange reason?

[Spoonbill]

Gone West, dont worry about it ;)
As an atco, I would pass you the xxxx Regional Pressure Setting, and all I'd expect is a correct read back, as would any flight examiner.
The vast of majority of the replies have attempted to be helpful, but it simply isnt worth worrying about, it's just a fact of aviation life.

[moggie]

Noggin- although RPS is not ideal for avoiding controlled airspace it is better than b*gger all. Iddeally, everyone has an IR, flies IFR in receipt of an air traffic sevice and flies high enough in their FMS equipped jets to all be on 1013.

Yes it is flawed but it is still better than nothing when operating OUTSIDE controlled airspace latterally and if operating UNDER controlled airspace you should be on something more appropriate or giving a good 1000' plus clearance. If I remember correctly (and I don't have a chart handy), most airways have their bottom level defined as a flight level so 1013 is a good setting. If they have an altitude as bottom level then RPS with 1000' should do (the RPS is unlikely to be over 30mb off the actual QNH/QFF).

[rolling circle]

"If (airways) have an altitude as bottom level then RPS with 1000' should do (the RPS is unlikely to be over 30mb off the actual QNH/QFF)."

From the AIP (ENR 1.7)

3.9 Airspace within all Control Zones (CTRs), and within and below all Terminal Control Areas (TMAs), Control Areas (CTAs) except Airways and the Daventry and Worthing Control Areas, during their notified hours of operation, do not form part of the ASR Regional Pressure Setting System.

3.10 When flying in airspace below TMAs and CTAs detailed above, pilots should use the QNH of an adjacent aerodrome when flying below the Transition Altitude. It may be assumed that for aerodromes located beneath such areas, the differences in QNH values are insignificant. When flying beneath airways whose base levels are expressed as Altitudes pilots are recommended to use the QNH of an adjacent aerodrome in order to avoid penetrating the base of Controlled Airspace.

Why invent procedures when suitable, published ones already exist? That is the way that accidents happen.

[bookworm]

I'm now convinced that Noggin is Henry Fowler, pedant of English grammar, risen from the dead. :)

I have no idea what "MET.O 630/AP3340 Capt 9" is. Aviation works with the framework of ICAO, which is often unpleasantly ambiguous. But imposing arbitrary restrictive definitions is not the way to solve that.

Annex 3 Meteorological Service for International Air Navigation does not define QNH, except in that it says that an altimeter "when set to a QNH altimeter setting will indicate altitude". It regularly uses the term "forecast QNH" or "forecast lowest QNH".

PANS-OPS Vol 1 (Doc 8168) describes QNH as an altimeter sub-scale setting to obtain elevation when on ground. It then goes on to say in the section on altimeter setting that an aircraft is "flown at altitudes determined from an altimeter set to sea level pressure (QNH)" [oh dear!]

UK AIP ENR 1.7.3.7 says:

"the UK has been divided into a number of ASRs for each of which the NMO calculates the lowest forecast QNH (Regional Pressure Setting) for each hour".

It seems pretty clear from the above that the Regional Pressure Setting is a QNH, not a QFF. I can also see nothing in the above that says that a QNH is measured at a point, and it's certainly not restricted to observed quantities.

QNH is a physical quantity, and it is no more restricted to a measurement site than a temperature -- you can only measure a temperature with a thermometer at a single point, but presumablly you don't object to the use of the term "forecast flight level 100 temperature" on the grounds that it could only be measured at one point at FL100. Temperature describes the physical quantity, whether forecast or observed, local or regional.

If it walks like a QNH and quacks like a QNH, it's probably a QNH... :)

[NextLeftAndCallGround]

Interesting to see that CAP 413 seems to use both Regional Pressure Setting and Regional QNH - is this what BlueLine meant about it being updated?

I'm afraid I'm with many others on this one - as a controller if someone asks for the 'XXX Regional Pressure Setting', the 'XXX Regional', the 'XXX Regional QNH', the 'XXX Regional Setting' or the 'XXX QNH', I know exactly what they want. If I'm in any doubt I'll check - that's the beauty of R/T.

I trust that GoWest is as correct and precise whenever he passes a position report or requests a clearance.

We're all human.

[40 yearflyer]

Can this discussion move on to the usefulness of RPS ? Why do we use them when no other country bothers ? Is it to cater for a non radio aircraft setting off an IFR flight of 2 hours that might take him,say, over Snowdonia - assuming he remembers to add 1000 ft (plus extra for mountain effect) to his MEF or obstacle -
I cannot see the relevance of flying past Coventry on Barnsley RPS when there is a low pressure system centred on Newcastle miles away but dictating the lowest RPS for that big area. Just as you announce your altitude you receive Coventry QNH and lo and behold it makes your altitude 300 ft different from the aircraft in that area. However, it doesn't matter we are all VFR -set what you want- see everybody don't we. Which leads me onto the next subject - how many times have I flown IFR into Coventry, Cranfield and any other 'training' airfield where aircraft are reported to me, as if I can see them, who are pretending to be VFR. The latest passed half a mile away VFR in a layer of SC stubbornly maintaining his altitude when he could have descended or climbed and I might have seen him earlier -if at all - 'cos I was IFR wasn't I

[Chilli Monster]

Anything flying near my airfield gets my QNH, because that's what the traffic in my hold is flying on and therefore separation is based on that. I'll give the RPS, but just before the aircraft goes off my frequency and is heading away from me. The airport to the south of me, with it's lump of associated class 'D', operates on QNH. I wouldn't dream of working an aircraft flying towards them and giving them the RPS because it causes too much confusion - QNH is best, always :D

CM