Regional Pressures

[funfly]

At the risk of looking dumb...
Can anyone enlighten me as to why our regional pressure (Barnsley) is almost always the same as our airfield QFE which is at 300ft amsl?
:confused:

[Farmer 1]

Pure coincidence, Funfly, I assure you.

Regional pressure is the lowest pressure in the ASR, forecast for the next hour, if my memory serves me well.

So, it should never be more than anywhere within the ASR. If it is, then the technical term is - a Cock-up.

Be patient, give it a couple of years and I'm sure you'll eventually see a day when there is a difference between regional pressure and QFE.

[Down Ampney]

In broad terms:
Aerodrome QFE is an actual pressure setting based on a recent measurement on site. At 300ft amsl the QFE would differ from an actual QNH at the same site by being about 10mb lower. (1mb equivalent to about 30ft at these levels).
However the regional QNH is
1. a forecast figure and
2. the lowest forecast QNH within the whole of the ASR
For terrain clearance safety reasons both factors drive the figure down. The forecast regional QNH will always be an underestimate. If the pressure differential across the Barnsley ASR is significant it is conceiveable the lowest forecast QNH would be 10mb below the QNH at your airfield. The regional QNH would then be equal to the airfield QFE.
In addition there might be some correlation between the geographical location of your airfield compared to the average pressure distribution across the ASR that produces the coincident figure so frequently.

[funfly]

I understand - the regional pressure may give you a higher amsl than a local QNH thereby improving safety height.
Thanks.

[2 sheds]

Funfly

You are not comparing "like" with "something like" in your original question. To compare a RPS with an aerodrome QFE is quite irrelevant. However, a cross-check with the current aerodrome QNH would be more useful to ascertain that you - or the Met Office - have not made an error. The RPS should always be either the same (possibly) or numerically lower for reasons that have been explained.

PS - why this obsession with QFEs and RPSs?

[Chilli Monster]

Ban them both I say (QFE and RPS) - the rest of the world manages with just two pressure settings - why can't we!

[Pierre Argh]

the rest of the world manages with just two pressure settings - why can't we!Well additional safety may have something to do with it... I presume you're talking from a UK Civil ATC perspective? UK Mil use QFE as their datum of choice and RPS away from the airfield environment. "Ban them" you cry... you presumably have big influence with HQ STC?

Chilli, I accept many other countries don't use RPS (but not so sure about QFE?); no one's forcing you to use them, but having them available has got to have some benefits? (Of the civil and military aircraft flying into an airfield in the SW, who for twelvve months have been given the option of using QFE or QNH... most elect to use QFE. What does that tell you?)

[2 sheds]

The military obsession with RPS and QFE would be fine if they did not expect, with the exception of low-level traffic using RPS, the rest of the world to accept handovers on those settings!

[Chilli Monster]

Of the civil and military aircraft flying into an airfield in the SW, who for twelve months have been given the option of using QFE or QNH... most elect to use QFE. What does that tell you?)

When asking to do the approach QNH one of your young ladies didn't give me the choice once - I got told I would be using QFE (which is not mine, nor many other operators SOP). I have no sway with HQ STC - but isn't it about time they recognised they were the minority airspace user in the UK ;)

The safety argument is a misnomer - most people calculate an MSA for a route - not an MSH. Approach plates also have obstructions marked as "amsl" - not "aal". Safety surely would be better served by everyone adopting common datums and learning to fly on them, rather than the chopping and changing dependant on the vagaries of the Airfield operator.

And I can confirm - most of the world happily does without QFE. Never had it given or offered whilst flying in Europe. As for extremes - try setting it at either Las Vegas (2181ft amsl) or Big Bear (6748ft) :) (or if you want to look outside the US try Nairobi at just over 5000ft).

[LXGB]

Talking of RPS.
My unit recently did away with giving it out to aircraft operating outside the MATZ (still using QFE inside the MATZ of course). All aircraft, mil & civ get the Airfield QNH now instead.
The RPS is still displayed on the totes and is available to aircraft on request. Seems to be working well, had no complaints.

LXGB

[Farmer 1]

There seems to be a lack of understanding as to why we use QFE and RPS in the UK. A couple of reasons for each immediately spring to my mind: safety and simplicity.

QFE: It is used only close to an airfield, not for en-route navigation. To do that would be dangerous. Using it enables me to remember the Decision Height for every single airfield in the country. It is always the same, no matter what the airfield's elevation is, impossible to confuse. Simple and safe. Heights and altitudes of obstructions are listed on airport plates. However, nothing compels you to use QFE. But to use QFE you need a low-lying area, like the UK. Trying to use it at places like Nairobi is a waste of time.

RPS: If you are flying across country, away from other airfields, remaining below the transition altitude, what other pressure are you going to use? The last airfield QNH? What if you fly into a depression, how do you know your safety altitude? If you set the RPS you can guarantee knowing it. Once set, it does not change until the next hour - safe and simple.

[Chilli Monster]

QFE: It is used only close to an airfield, not for en-route navigation. To do that would be dangerous.

Any chance you can pass that pearl of wisdom onto a certain military unit (one of only two with their particular type of airspace) who insist on handing over transit traffic, outside their CTR, on the QFE :uhoh:

RPS: If you are flying across country, away from other airfields, remaining below the transition altitude, what other pressure are you going to use?

Working on the basis that a) the UK is not a large country (if the pressure difference is that big you wouldn't be flying); and b) you're going to have to call an ATC unit for that regional pressure; then why not dial up a nearby ATIS and use that airports QNH? Might also have the added benefit of not busting CAS when the lower level is defined as an Altitude. (RPS in this situation having the effect of putting you inside CAS when you think you're outside).

Just an idea - might be worth considering

[2 sheds]

However, nothing compels you to use QFE. But to use QFE you need a low-lying area, like the UK. Trying to use it at places like Nairobi is a waste of time.

Quite right, but two points...

I was under the impression that various military units actually imposed QFE reference on civil transits of their MATZ or CTR.

If you are going to mix and match depending on the aerodrome elevation, therein lies a potential problem in itself - getting away from a standard operating procedure - hence the "use QNH as a norm" argument.

[Farmer 1]

Don't know about that one, 2 sheds, it's a long time since I penetrated a MATZ. However, judging by the posts, things might have changed, in which case I am out of date (I'm not flying in the UK at the moment). But, if my memory serves me well, which it probably does not, QFE was only ever used for circuit traffic. Airfield QNH was used for transitting, and having transitted, RPS was reset.

For a while, I remember the RAF decided not to use QFE. New man at the top, I believe. During that time I always asked for, and was given, QFE. After a while there was a new new man at the top, and common sense prevailed once more. It makes life easier, believe me.


Working on the basis that a) the UK is not a large country (if the pressure difference is that big you wouldn't be flying); and b) you're going to have to call an ATC unit for that regional pressure; then why not dial up a nearby ATIS and use that airports QNH? Might also have the added benefit of not busting CAS when the lower level is defined as an Altitude. (RPS in this situation having the effect of putting you inside CAS when you think you're outside).



I agree totally, Chilli, in that the UK is not a large country - could not disagree with you less on that one. However, it is still big enough for a depression to constitute a potential danger if flying into it; and it is still big enough to have areas remote enough and wild enough to be out of VHF coverage. Put those together, and I cannot recommend too strongly that you use the correct altimeter setting. You might have the option of not flying in those circumstances, but you would need to be pretty convincing to persuade an employer or a client.

Please allow me to try another tack: we are talking here about flight safety, in particular being able to ensure you are flying at a safe altitude over a remote area.

The greatest difference I can remember between airfield and regional pressures was equivalent to over 500ft. Obviously, a depression was approaching, but flying continued unabated, without any undue problem. If I were to fly over high ground, with RPS set, in my example that would give me an extra 500ft of safety margin, and I would have that extra margin for the next hour. Clever people work out this pressure for me, and I am grateful to them for the service.

On the other hand, you would presumably set airfield QNH and set off into an area of lower pressure. Immediately, your altimeter starts overreading, and your safety margin is reduced. Not by much, I grant you, but by a finite amount, while mine has increased. And how often are you going to update your setting, or more importantly, just how, if you lose VHF coverage?

Safe flying.

[Chilli Monster]

On the other hand, you would presumably set airfield QNH and set off into an area of lower pressure. Immediately, your altimeter starts overreading, and your safety margin is reduced. Not by much, I grant you, but by a finite amount, while mine has increased. And how often are you going to update your setting, or more importantly, just how, if you lose VHF coverage?
Safe flying.

No - I'm either going to a) follow the procedures I've stated before before or; b) Be flying IFR iaw with Flight Levels ( a more sensible arrangement when the UK Transition Altitude is mainly 3000ft).

I'm sorry - the argument doesn't hold up. You still haven't addressed the problem of how you're going to obtain the RPS. Your "Setting off into a depression" scenario, with reference to altimetry in the UK scenario, is a throwback to flying 80Kt cruising speeds in IMC in a UK of many years ago - not today where better solutions and options are available.

[Farmer 1]

RPS: If you are flying across country, away from other airfields, remaining below the transition altitude, what other pressure are you going to use? The last airfield QNH? What if you fly into a depression, how do you know your safety altitude? If you set the RPS you can guarantee knowing it. Once set, it does not change until the next hour - safe and simple.

If you are going to fly above the transition altitude, then you still need to know your minimum safe altitude. Away from an airfield, you do not know the local pressure, which is why you should use the RPS. You obtain the RPS by asking for it - from the last airfield, or from the FIS.

Even now, in this modern day and age, with gps and all, people still manage to fly into cumulo granite in bad weather.

Chilli, shall we agree to differ? If our paths cross one day I'll give you a friendly wave from above.

Farmer.

[Chilli Monster]

And people wonder why GA never seems to move ahead - no surprises really when you see how entrenched people in using such old fashioned, anachronistic items.

You obtain the RPS by asking for it - from the last airfield, or from the FIS.

And what's stopping you getting a more relevant, more accurate pressure setting (QNH) from the same source? :rolleyes:

[Pierre Argh]

"more accurate, more relevant pressure setting"... of course QNH is more accurate, but "relevant"... only in certain circumstances? If you departed from the Isles of Scilly for, say, White Waltham, transitting below 3000ft what pressure setting would you use... QNH, which would be OK for about the first 20-30 miles but become increasingly less accurate as you progressed along your route. RPS has a built in safety factor, and is available in advance (so you could even obtain pressures for your entire trip before departure)

It also means that in airspace populated by several airfields everyone using RPS is flying on the same setting... believe me QNH can differ by a couple of millibars over quite a short horizontal distance. As for Chilli's reply to my earlier post about using both QFE and QNH... and him being told he had to use QFE. Use of this datum is still mandated by HQ STC, but it is to be made available for "in cockpit use", so he only had to ask... Currently, a few UK military airfields are happy to accept QNH based procedures, and procedures are currently being drawn up that should increase the scope for QNH Ops elsewhere.

I also couldn't agree more that the RAF is a minority airspace user, considered colectively. But would suggest that perhaps on an operator to operator basis they are as large if not larger than any other single user in the UK... their procedures are based on experience formulated with a high regard for Air Safety. Switching to QNH is regularly considered as an option, but has so far been ruled out (except for one, frankly badly managed, excursion in the 80s)... but shouldn't be discounted in the future.

[bookworm]

"more accurate, more relevant pressure setting"... of course QNH is more accurate, but "relevant"... only in certain circumstances? If you departed from the Isles of Scilly for, say, White Waltham, transitting below 3000ft what pressure setting would you use... QNH, which would be OK for about the first 20-30 miles but become increasingly less accurate as you progressed along your route. RPS has a built in safety factor, and is available in advance (so you could even obtain pressures for your entire trip before departure)

So's a chart with isobars and the QNH for your destination! In the very unlikely event of being unable to update your setting with real, observed QNHs due to comms failure, it's not hard to do rather better than the RPS as an estimate.

But that's beside the point -- if you want to write down RPSs for emergency purposes in advance of a flight, go ahead. Just don't ask me to set it on my subscale when there's a perfectly good QNH available!

It also means that in airspace populated by several airfields ... is flying on the same setting...

That would be "clutch QFE" then? ;)

If a group of airfields in proximity want to use a common QNH for separation (e.g. like, er, London), let them pick an airfield (e.g. like, er, Heathrow) and use the QNH. Why use something irrelevant like RPS?

[Pierre Argh]

I am aware of "Clutch QNH" but cannot recall a single incidence where a dozen or so independant minor airfields, micro-light landing strips etc, in the UK over say, a 40nms radius area have co-operated in this manner... Bookworm, can you enlighten me?

Suppose you departed from Minor Airfield A, remain in the vacinity of A but call me at Major airfield B, 25nms away, for a FIS... if you wish to remain on QNH(A) how would you expect me to be able to update you on pressure changes? Or you might insist on using my QNH, the pressure differential over 25nms might not be great, but may not be insignificant? Let's take this a step further...

If you're VMC... 2500ft QNH(1013mbs) is the same as 2410ft RPS (1010mbs) and makes little difference to the price of fish, but then you go IMC and there is high ground and obstructions around... it seems to me obvious which is the safer setting to use and therefore what pressure I will pass as a norm to transiting aircraft... Just because the majority do something different doesn't make it right, or the best solution? But then I'm just the one sat on the ground trying to help?

[DFC]

Pierre,

Your argument about several airfields in close proximity goes against the stabalishd procedures for operations within and under the London TMA. All aircraft ther use the "London QNH" which is the QNH from any suitable airfield within or below the TMA. The differences are according to the CAA not considdered to be significant.

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Farmer 1,

Can you elaborate on your statement: "Using it enables me to remember the Decision Height for every single airfield in the country"?

In my book, the decision height depends on the procedure, system minima and obstacle environment which are not the same for every airfield.

France does not have RPS and has terrain higher than the UK. Ireland does not have RPS and covers an area as big as England if one incluses SOTA and NOTA. Our nearest really remote area - Shanwick OCA does not have RPS. Why not?

--------

When landing Visually one can see the runway and obstacles - an altimeter is unnecessary. When flying the visual circuit, the altimeter enables one to fly at the published level. That could be done with the altimeter set to QFE, QNH, RPS or 1013 provided that the pilot flies at the appropriate level.

When flying IFR, all the obstacles published are AMSL even close to or on the aerodrome. Thus QNH provides better situational awareness. Until visual provided that the appropriate procedure is followed flying on QNH or QFE makes no difference. Once visual, refer to above comment regarding visual landing.

If however, one uses QFE and does not become visual, failure to reset the QNH at a very busy part of the flight is a) Dangerous and b) one of the most common cause of IR test failures.

I also think that using QNH for take-off, landing and circuit work improves situational awareness with regard to performance. For example take a PPL and get them to do a few circuits on QFE - they take-off at 0, downwind at 1000 and land at 0. No problem. Take them to an airfield 5000ft AMSL (with an altimeterb that could set the QFE). Again they take-off at 0, downwind at 1000 and land at 0.

Would it not be safer to have the PPL sit there and say "heck this airfield is high I better check the figures, lean the mixture and make a best performance take-off as per the POH.

QFE is used because of...........tradition. No other reason.

As Chilli says. Time to bin it.

Regards,

DFC

[Canary Boy]

QFE is used because of...........tradition. No other reason.
As Chilli says. Time to bin it.
Cr*p! It is used because the aircrew want to use it. The service Military ATC provides is geared to enabling 'Military aircrew to operate safely and effectively, with tactical freedom, etc'. Hence the use of RPS, QFE, QNH, SAS and, if required, QNE! As far as being 'forced' to adopt a certain pressure setting - it shouldn't happen; and the handover to an adjacent unit should most certainly NOT be on QFE.
Aircraft flying relatively low in close proximity to a mil airfield will routinely be placed on QFE in order to make separation with vis/radar circuits easier - once away from the circuits the appropriate RPS(s) will be offered, if the crew would rather use a different setting (a QNH) they merely have to say so!

[London Mil]

Regional QNH is still valuable for military low level let downs and fighter control type ops. It is used extensively within/below the North Sea MDAs where the nearest airfield can be 200+nm away. CM, find me an airfield off the West coast of Scotland where one can obtain an accurate QNH. Finally, if military pilots were to float around on airfield QNH at 420kts, in some areas they would spend their whole sortie tuning into various ATC agencies trying to ascertain the nearest correct pressure setting.

I understand RPS it is also extensively used by the oil industry helicopters.

QFE vs QNH, well there's always going to be 2 schools of thought. As an air taffic controller, I wish that we only used one pressure setting. As a Pilot, I don't care, as long as I remember which one I am using! It is not a difficult concept to grasp.

[DFC]

Canary Boy,

The reason why I say it is tradition is because the average RAF intake does not know very much about altimeter settings until they learn what the traditional system is. If the RAF had kept to the QNH system in the late 80s, the pilots qualified in the past 10 to 15 years many of whom ae now the QFIs would not know about QFE ops and would not be passing on the tradition.

-----------

London Mil,

The reason as far as I am aware for the North Sea helis using a common altimeter setting is because very often they are IFR at or below the transition altitude (to stay out of icing). When things are busy on the defined tracks it is a great idea for IFR flights to have a common altimeter setting for separation purposes. There is also an advisory service provided to those flights. In fact I think that the place is so busy for ATC that no other flights are allowed at the moment over a large part of the area due to one of the radar heads being out of action.

Since the Mil are in such need of RPS, how many RPS areas are there in say Iraq, Saudi, Afganistan and other places round the world?

Would it not be better for military training to reflect the operational realities of operating in the back end of nowhere at short notice while under pressure?

As for having to call ATS for QNHs. That is old hat with data link technology available the nearest QNH can be available at the push of a button.

Terrain following radar and rad alts of course dont need RPS! :)

Regards,

DFC

[Pierre Argh]

DFC... Regional Pressure Settings provide a safe, low cost alternative, a fall back. Whilst you argue elegantly for the use of other pressure settings in various circumstances (he flatters), I don't see many convincing arguements for doing away with RPS altogether, other than that no one else in the world thought of the same good idea?

[2 sheds]

Leaving aside the merits of the argument for a moment, you will not believe what is on the Met Office's own website.

I quote...

"QNE is used to set the altimeter to the standard International Civil Aviation Organization atmosphere setting and assumes a sea-level pressure of 1013.2 hPa regardless of actual conditions. This setting is only used by aircraft cruising at high altitude and serves to ensure safe separation of aircraft.

QNH is used to set the altimeter to read the actual height above sea level in the local area, with the UK split into 20 different areas. All low-level aircraft use the QNH setting, including private aircraft, gliders, fast military jets and large commercial aircraft. The Met Office issues forecasts of all 20 QNH values every hour - coded FOQNH. Each forecast is for the lowest sea-level pressure value expected in the area during the hour".

[Note for the Uninitiated or the Easily Confused - ignore all above!!!!]