Regional Pressure Setting (RPS) or Regional QNH - do we need it? Do you use it?

[Jumbo Driver]

I have long wondered about the continued usefulness of what some may now regard as the somewhat outdated concept of the Regional Pressure Setting (RPS) or Regional QNH. Its use is outlined in AIP ENR 1.7 (http://www.nats-uk.ead-it.com/aip/current/enr/EG_ENR_1_7_en.pdf) para.3.7 et seq., and CAP410 (http://www.caa.co.uk/docs/33/CAP410__PARTA.PDF) (qv) also provides a helpful definition:

Regional Pressure Setting
The Regional Pressure Setting is a forecast of the lowest QNH value within an altimeter setting region. The values which are made available hourly for the period H + 1 to H + 2, are given in whole millibars.
However nowadays, many pilots seem to be unaware of the way the RPS is calculated and even its possible implications for their flight. There is just a tendency to set it anyway on departure. It will, of course, provide an over-safe (but therefore inaccurate) indication of terrain clearance within a given area for a period of up to 2 hours ahead; however there are traps for the unwary, who perhaps do not understand the problems of using it near, or especially under Controlled Airspace. The far better alternative, surely, is to use an appropriate aerodrome QNH for the flight? Since a locally obtained aerodrome QNH is not only relatively easy to obtain but undoubtedly more accurate in terms of correctly indicating height over terrain, perhaps we should question the point of continuing to routinely set and use the RPS?

While it is used in the theoretical calculation of the lowest usable FL in an airway which has a base near the TA, the setting itself is not actually used in the aircraft in that process. Regional Pressure Settings do have some use in the specialised areas of maritime reconnaissance operations and also in vertical separation of North Sea helicopter off-shore operations in the Anglia OSA (ENR 1.15 (http://www.nats-uk.ead-it.com/aip/current/enr/EG_ENR_1_15_en.pdf) para.1.5.5). However, in normal civilian use, with the possible exceptions of an extended non-radio flight remote from any airfield, over significant terrain and in a rapidly changing synoptic situation (when arguably one shouldn't be flying anyway!), or a flight when the pilot is so totally lost and could be anywhere in a large area (AIC 21/2006 (http://www.nats-uk.ead-it.com/aip/current/aic/yellow/EG_Circ_2006_Y_021_en.pdf)), I really can't see the point in using the RPS.

What do you think ... ?


JD
:)

[Lurking123]

I'm just wondering how many pilots would seek out the 'real' QNH and how they would get it. Some would be pragmatic and use the QNH they got airborne with, whilst others would fastidiously call every single ATC unit on their route to confirm the QNH.

I don't particularly have a view on RPS, I'm more bothered about the variable Transition Altitudes the UK appears to be developing.

[Whopity]

It was designed for RAF Shackletons so that they could operate IFR safely below 3000 feet. I'm sure they find it very useful!

If we are the only country in the World to have it, we must be way ahead of the rest!

[DB6]

Lurking 1213.....ATIS?

[madlandrover]

RPS? Horrible thing. "Safe" but inaccurate. Round here the RPS (Barnsley) is almost always the same as our QFE, with a 280' amsl aerodrome. Unfortunately the local LARS unit really prefers us to use the RPS for altitude reports, but they're also pretty good at advising the actual difference between these altitudes and the bases of controlled airspace around.

They may be appropriate in isolated areas like Northern Scotland, but otherwise fairly pointless when ATIS reports or FIS etc are available.

[Duchess_Driver]

I'm just wondering how many pilots would seek out the 'real' QNH and how they would get it.


The conversation goes something like.....


" G-XX, Cotswold QNH 1000'

Request Brize Norton QNH

G-XX, Brize Norton QNH 999

999 G-XX "

Simples!:ok::ok::ok:

[Lurking123]

So the Brize QNH was lower than the lowest forecast QNH? :cool:

[Duchess_Driver]

Touché mate!

Reminder to self...engage brain before fingers!

[usedtofly]

I fly in the North of Scotland where the pressure can change by up to 20 mb in one flight over 200 miles. So depending on which way the pressure change is, the regional QNH is VITAL

:eek:

[Keygrip]

Just jumping on bandwaggon - remember, if the pressure drops below one thousand then you must add the word "Millibars" (despite the hectopascal world).

So, from DD's post above,

"Cotswold QNH 1000, Brize Norton 999 millibars"

<edit: typo>

[Jumbo Driver]

I fly in the North of Scotland where the pressure can change by up to 20 mb in one flight over 200 miles.

Exciting stuff ... by my reckoning, that pressure gradient would correspond to a geostrophic wind of around 80kts ... do you often fly in that ... ?


JD
:\

[Tinstaafl]

We did when I flew Islanders in Shetland although ground ops were limited to 50kts due to a door opening limit. Could manage more but we needed the fire truck to park a couple of feet in front of the nose to act as a windbreak. I've had a 240kt GS (125-130kt TAS) more than once at only a few thousand feet. Would hate to see what my holding patterns over Sumburgh would have looked like while waiting for ATC or FISO to arrive so I could do an approach.

[Jumbo Driver]

So, are these exceptional situations any justification for retaining what many now regard as an anachronism?


JD
:)

[usedtofly]

Exciting stuff ... by my reckoning, that pressure gradient would correspond to a geostrophic wind of around 80kts ... do you often fly in that ... ?

Sometimes its over 100 kts! We are limited to 60 kts on the ground tho'.

As for 'often'.....well we have no choice, the operation is 24/7

It IS fun tho' :E:E:E

[Tinstaafl]

One needs some sort of altimeter setting, and not everywhere has a convenient H24 ATIS broadcast.

Rather than the UK's RQNH, I prefer Oz's Area QNH. The difference is that AQNH in Oz isn't the *lowest* for an area but is more like a QNH expanded to cover a large area accurate to within a few mb. If the difference becomes greater than 5mb then the area is subdivided to make sure there is never more than a 5mb step from one boundary to the next.

[fireflybob]

Jumbo Driver - am with you on this one - I would vote to get rid of the RPS. Trouble is the military seem to like using it to use to compute such things as Minimum Height to Commence Recovery (from Spinning, for example) although, if my memory serves me correctly this is based on the Transition Level which, at most UK military aerodromes, is based on (you've guessed it!) the RPS.

Mind you whilst we are about it we could bin the QFE too - how much simpler life would be if it was just an aerodrome QNH!

(Pith helmet suitably donned)

[usedtofly]

Fireflybob.

how much simpler life would be if it was just an aerodrome QNH!

In my company we ONLY use QNH due to company ops, however I do sometimes think that at least QFE does make you think just how much (little!) space there is between the a/c and the ground when flying down to minima on an ILS :eek:

[Lurking123]

fireflybob, you're talking bolleaux. The TL is based on the TA which in the UK is predominantly 3000ft (or some other figure depending upon whether you're below various bits of CAS). The TA is based on aerodrome QNH which, spookily, is derived by formula (ie it isn't necessarily an accurate figure) from the QFE. Despite best efforts, most airfields don't dig a bleedin' deep hole down to msl to drop a barometer down :p)

Good reason for QFE

LiveLeak.com - Thunderbirds Ejection, how it happened. (http://www.liveleak.com/view?i=d74_1235356158)

[fireflybob]

fireflybob, you're talking bolleaux.

Lurking123, thankyou for the compliment but I did state:-

although, if my memory serves me correctly

I am grateful for your correction because that's how we learn, just no need to use such colourful language.

[Lurking123]

We're in a democracy and are entitled to different opinions.:)

[Jumbo Driver]

We're in a democracy and are entitled to different opinions.:)

... certainly, but sometimes it's the way those opinions are expressed that can be pivotal ... ;)

JD
:)



CRM ... mutter, mutter ...

[dont overfil]

Out in the uninhabited areas of Scotland we only have the RPS or 1013.
I'd rather have the safe Orkney RPS over high ground than an optimistic one from an AD over 100 miles away.
The whole idea of the thing is that everyone is flying on the same setting outside controlled airspace in a given setting area.
DO.

[SpannerInTheWerks]

If you're flying from a private site, that is one without ATC, which QNH value would you use to fly cross-country?

One derived from the aircraft altimeter 'adjusted' from the airfield elevation setting, one published on the 'web' before flight or the Regional QNH obtained from ATC?

How would you determine the base of controlled airspace defined as an altitude? Maybe some don't care enough to bother? I remember having my Silver height attempt disallowed years ago because the instructor worked out, with the prevailing Regional QNH, I would technically have JUST been in controlled airspace - not so if I based the climb on the pressure setting for the airfield at the time (a bit tight that I always thought?!).

I might have expected this conversation on a private flying forum from an inexperienced pilot asking a genuine question due to lack of understanding, but on a forum inhabited by 'professional' pilots I find the subject surprising.

SITW :)

PS: Not to mention 'collision avoidance' issues!

[Jumbo Driver]

... I might have expected this conversation on a private flying forum from an inexperienced pilot asking a genuine question due to lack of understanding, but on a forum inhabited by 'professional' pilots I find the subject surprising.

I'm not quite clear which subject it is you find surprising ... ? If it is my original question (i.e. the topic of this thread), it was after some consideration that I posed the question on this forum because I felt it was likely to prompt more erudite and informed answers (perhaps) than elsewhere. ;)

My question was - and still is - not how we should use RPS but whether we still use and need it.

If you're flying from a private site, that is one without ATC, which QNH value would you use to fly cross-country?

As a regular flier from a private site, I am perfectly happy, knowing the elevation of the strip, to wind that altitude on the altimeter, thus providing my own "derived" local QNH. I don't think there is any doubt on this forum that, for any foray under CAS where the base is expressed as an altitude, an appropriate aerodrome QNH should be used.

... or perhaps I have misunderstood your post ... ? :confused:


JD
:)

[fireflybob]

As a regular flier from a private site, I am perfectly happy, knowing the elevation of the strip, to wind that altitude on the altimeter, thus providing my own "derived" local QNH. I don't think there is any doubt on this forum that, for any foray under CAS where the base is expressed as an altitude, an appropriate aerodrome QNH should be used.

Jumbo Driver, agree totally.

Another reason against QFE is potential bust of the bottom of controlled airspace if you depart on QFE and then omit to set QNH on/after departure especially where the departure elevation is relatively high. An example is Biggin Hill below the London TMA which is circa 600 ft amsl and there has been at least one documented case of this happening.

[Lurking123]

JD, I agree there is absolutely no doubt at all. The doubt is when people make factually incorrect statements. My point was that the military do not use RPS to calculate the TL. Like everyone else, they use the airfield QNH. :ugh:

[dont overfil]

Setting a QNH from the known elevation of the strip is fine for a bimble round the field but does nobody on here actually go anywhere?
Surely even full time flying instructors must go further than 50 miles from their home field.
DO.

[Islander2]

How would you determine the base of controlled airspace defined as an altitude? Maybe some don't care enough to bother? I remember having my Silver height attempt disallowed years ago because the instructor worked out, with the prevailing Regional QNH, I would technically have JUST been in controlled airspace - not so if I based the climb on the pressure setting for the airfield at the time (a bit tight that I always thought?!).

I might have expected this conversation on a private flying forum from an inexperienced pilot asking a genuine question due to lack of understanding, but on a forum inhabited by 'professional' pilots I find the subject surprising.SpannerInTheWerks, others may find it surprising you don't seem to understand that the base of controlled airspace defined by an altitude is with respect to the QNH of an aerodrome situated beneath the controlled airspace, not with respect to the RPS! AIP ENR 1.7 refers.

Or perhaps you do, and I too have misunderstood your post. Perhaps you'd care to clarify the answer you had in mind for your own question:
If you're flying from a private site, that is one without ATC, which QNH value would you use to fly cross-country?

One derived from the aircraft altimeter 'adjusted' from the airfield elevation setting, one published on the 'web' before flight or the Regional QNH obtained from ATC?And in the process, explain how your answer is supported by your curious footnote:
PS: Not to mention 'collision avoidance' issues!