Is there such a thing as "Regional QNH"?
 

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?

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

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.

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 ]

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.

The AIP 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!

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).

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!

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:

That might well be WMO-standard.

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

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. ;)

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?

<<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 )

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 ]

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.

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.

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.

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.

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"

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?