Regional Pressures
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Regional Pressures
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?
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?
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Re: Regional Pressures
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.
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.
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Re: Regional Pressures
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.
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.
Re: Regional Pressures
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?
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?
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Re: Regional Pressures
the rest of the world manages with just two pressure settings - why can't we!
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?)
Re: Regional Pressures
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!
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Re: Regional Pressures
Originally Posted by Pierre Argh
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?)
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).
Last edited by Chilli Monster; 14th Jan 2006 at 17:45.
Re: Regional Pressures
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
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
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Re: Regional Pressures
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.
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.
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Re: Regional Pressures
Originally Posted by Farmer 1
QFE: It is used only close to an airfield, not for en-route navigation. To do that would be dangerous.
RPS: If you are flying across country, away from other airfields, remaining below the transition altitude, what other pressure are you going to use?
Just an idea - might be worth considering
Re: Regional Pressures
Originally Posted by Farmer 1
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.
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.
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Re: Regional Pressures
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.
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.
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.
Originally Posted by Chilli Monster
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.
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Re: Regional Pressures
Originally Posted by Farmer 1
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.
Safe flying.
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.
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Re: Regional Pressures
Originally Posted by 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.
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.
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Re: Regional Pressures
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.
And what's stopping you getting a more relevant, more accurate pressure setting (QNH) from the same source? 
You obtain the RPS by asking for it - from the last airfield, or from the FIS.
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Re: Regional Pressures
"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.
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.
Re: Regional Pressures
Originally Posted by 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)
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!
Originally Posted by Pierre Argh
It also means that in airspace populated by several airfields ... is flying on the same setting...
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?
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Re: Regional Pressures
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?
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?
