Pressure settings under a TMA
 

Apologies for what is I'm sure a simple question, but I'm a simple soul...

BLUF - what pressure setting do I need to use when flying under the London TMA? I'm assuming the London Regional QNH?

Background - I'm a low hours PPL living in carrot cruncher land, where the skies are open, the vistas superb and there are always a plethora of suitable looking fields to force land in if the donkey were to stop making the normal noises. BUT, I want to challenge myself, want to fly further and do more things. Some mates of the wife live in Southend, so I've done a bit of flight planning and reckon that a visit from here to there is perfectly possible, so long as I can sneak under the London TMA. But that puts me below the transition altitude and therefore flying on a local QNH. The last thing I want to do* is infringe some airspace and incur the inevitable wrath of the headmaster, which then raised the question of how is the base of the TMA calculated.

*Not strictly true - I think I'm even more allergic to crashing.

How about just asking ATC and let them give you the appropriate QNH before?

Good answer. But I like learning and I enjoy planning. I'd also rather know now for certain than be distracted by uncertainty at a point in the flight which is likely to be fairly high workload - and high stress - and wondering about whether I've got it right or wrong at that point isn't going to help me.

Remember, I'm a yokel. I'll already be digging out my best wellies for a trip to (near) town. I don't want to have to give myself a nosebleed by upsetting the CAA.

When flying under controlled airspace you use the QNH of any airfield under the controlled airspace. The regional pressure setting is designed to guarantee you won't hit the ground; it can't also guarantee not to put you too high, so you can bust airspace following it.

If you haven't already got a QNH of a suitable airport you can pick one up from an ATIS, or you can ask a controller. In the case of London you can ask for "London QNH" without worrying about particular airfields - they'll give you one that can be used to avoid airspace busts.

As an extra safeguard against mis-reading or mis-setting the altimter, most aviation GPS-based nav systems (such as Skydemon) have altimeter readouts based on sea level datum, equating (reasonably accurately) to local QNH.

Let me emphasise again what Gertrude said Do not use the regional pressure setting!
If the base of controlled airspace is given as an altitude on the chart, use QNH of any airfield under it (as already mentioned) if it's given in flight levels, use 1013 but remember what a big difference in actual pressure will mean in terms of your height above the ground.

Regional Pressure Settings (RPS) are the lowest forecast pressure for geographical areas across the UK and may be used for checking terrain clearance. As such they are something if an anachronism dating from times when many aircraft operated without radio, or internet access, and travelled significant distances. The effectiveness of RPS may be judged by the number of high ground wrecks that scattered this country.

Despite what it may say in some documents, RPS are not a QNH, which is the sea level barometric pressure for a specified location at a specified time and, in these information overloaded times, can be readily obtained from ATIS, ATC and online sources through such amazing technologies as Sky Demon, iPhone and Android apps and so on.

Anyone planning to operate in the vicinity of any form of Controlled AirSpace (CAS) where the base is defined as an altitude would be well advised to use the QNH of the nearest or most appropriate airfield. A look at the relevant chart will provide clues. e.g. Daventry CTA around Stoke on Trent; base 4,500ft use Manchester QNH, Manchester Low Level Route; the clue is in the name, but as the QNH at Manchester and Liverpool are usually the same use Manchester QNH, London TMA around Chelmsford; base to north 2,500ft, to south west 3,500ft use either Stansted or London QNH

As a former controller I always hated having to file reports on airspace infringement which were in the vertical plane, however, so many of those were caused by people operating on an RPS believing that they were remaining below CAS.

My own view is that the use of RPS is unnecessary and the sooner we all operate on QNH and plan carefully, the better.

I think I might be a bit careful using that method if planning to fly anywhere near the base of controlled airspace. That altitude measurement equates pretty much to a QNH of 1013. If the real QNH is 1003, that's 300 ft difference. For instance, if you were planning to fly at, say, 2300 ft through the Luton Stansted gap and used that readout........ :ooh:

If you are flying near controlled airspace: at best get a LARS service or, if you can't or don't want to do that, use a listening squawk. That way you should get a warning if you are about to infringe. I say SHOULD because it's still your responsibility not to. :ok:

This whole issue stems from the idiotic organisation of airspace and traffic services in the UK. At all other places I know, each one given point, as defined by latitude/longitude/elevation, belongs to one and exactly one part of airspace, with one and exactly one service in charge. So, depending on where you are, you call the relevant service and they tell you what QNH to set. Solved. Why the UK absolutely wants all this vagueness and confusion is beyond me.

For exactly the same reason as why we need Basic, Traffic, Deconfliction and Procedural services which, AFIK, almost nobody outside the UK understands.

You have to accept, Jan, it's not the UK that's out of step: it's the rest of the World.... :p

:broad smile:

Transponder Mode C altimeter readouts are referenced to 1013 hPa. GPS altimeter readouts are referenced to mean sea level.

I would agree with those who say that UK altimeter settings are far too complicated and therefore prone to human error. Local QNH below TA and 1013 above would reduce such errors (and the likelihood of airspace busts).

I haven't set QFE on an altimeter for 25 years. Given a QFE-referenced MATZ transit I fly QNH plus field elevation rounded up or down to the nearest 100 feet.

Yes. My point wasn't that a GPS altitude is in some weird way referenced to 1013, but that this is more or less the pressure at which the barometric altitude and the GPS altitude will be the same absent the offset that we enter in the Kollsman window to effectively bring them back into agreement with each other when reading off a barometric altimeter.

BS

How does that differ from this?

I have done a considerable part of my flying to / from airfields under the London TMA.

If you come from the north, talk to Farnborough North on 132.800
If you come from the South-East, talk to Farnborough East on 123.225
If you come from the West, talk to Farnborough West on 125.250
If there is nobody there - talk to London Information on 124.600 (if memory is right)

All of which will be happy to provide you with a Basic Service (or if Farnborough, they will happily pass on Traffic and Deconfliction services providing controller workload). They will pass on the local QNH on first contact with the ATC unit.

Bear in mind the accuracy of the altimeter vs accuracy of transponder reported altitude - as a general rule I make sure to be at least 100ft below the TMA, I often fly at 2,200ft to avoid the possibility of accidental zone incursion. There are a few "corridors" which are a little tight, and you need to keep a good lookout at all times. ie: between Luton & Standsted where there are a few airfields in between, and relatively stringent crossing requirements and between Heathrow and Gatwick where you have people from Redhill, Kenley and Biggin. It has never been an issue for me, but just "keep your eyes peeled, and your ears flapping"!

If you need any more help with your flight planning - I'd be happy to help!

Good Luck For Your Flight!
Alex

@PW: if your "BS" means what I suppose it to mean, well, err, I am really disappointed, I always respected you for a polite gentleman.

I gladly agree that Belgium, like most countries, knows the concept of a "Regional QNH" though, AFAIK, the UK is the only country to base it upon forecasts rather than upon actually measured pressures.

But that was not my point. I do not want to argue the merits of the "regional" setting, it has its advantages and its disadvantages, I can see how it came to be though it might indeed be considered an outdated concept.

Neither was it the point of the topic starter. My point was and is that in BE (and, as far as I know, all over Europe except in the UK) the opening question has an easy and unambiguous answer: if flying at a place such and such, determine in what bit of airspace you are, and talk to the service (the one and only!) in charge of that bit of airspace. They will tell you what setting to apply; in fact, most of the time they will tell you the QNH on your initial call for entering their area. Basta. Everything clear. And you know you will have the same setting as any other aircraft nearby, if their pilots followed this easy procedure; as they must.

Also - I just found this about Farnborough radar... A little out of date - but the information http://flyontrack.co.uk/wp-content/u...1/EGLFLARS.pdf is still pretty accurate.

Remember that Southend now has a class D zone around it, and contact them well before getting close to the boundary. They are still very much a GA friendly airfield though, never been badly received there, ATC have always been really nice and the landing fees were still cheaper than Shoreham (Brighton) but you get to land after an Easyjet which is a bit different. Could be worth giving them a call ahead though to know if they're expecting a lot of commercial traffic during the time that you're thinking of arriving (so as to miss the rush!)

Hope this helps.
Alex

Jan,

I am sorry if you found BS distasteful and admit that rubbish would have a response better suited to your description of the organisation of airspace and traffic services in the UK as idiotic.

You have many misconceptions about aviation in the UK and the best way to remedy that is to come over in your microlight. You will be presently surprised.

OK, fair enough.

(regarding a visit to that haunted airspace :) : I will be pleased to visit the UK, as soon as I am legally allowed to fly high enough to always remain within glide distance of terra firma - which I am afraid might take some time. Always have a plan B is my motto, and it has served me well; and ditching my high-winger in the English Channel is not a valid plan B for me. Yes yes, I do know it's only a couple of minutes and countless people have done it and yes, I know the engine doesn't know it is over water. That is exactly my reason to always want a Plan B: the engine can quit at any time, including those few minutes when I cannot glide to land. If the engine did know it was over water it could promise me to not fail right then - but it cannot. End parenthesis)

As for my misconceptions: I am willing to learn better, feel free to explain what I have misunderstood about the organisation of UK airspace and services. I still understand that at many places, pilots have a free choice of whom to talk to and that seems very unnatural to me, and needlessly confusing, and a potential cause for miscommunication.

As for my _many_ misconceptions: which are the others?

Thank you one and all, some useful info there. I especially like the Farnborough LARS leaflet, I shall re-read that more than once to ensure all is fully understood. And I think I'll have a good chat through with an experienced chum before I start to think too seriously about it. I may even pop back into the flying school and ask them to cast an eye over the scribbles I've drawn on my chart to double check I've not missed the obvious anywhere.

Airpolice - I'd dearly love to go through the TMA with a choice of altitudes available to me, but on my chart it's shown as Class A airspace, and as I hold only a PPL and no IR, I'm not allowed to - for jolly good reasons which I fully understand. A 'spam can' isn't of nearly the same performance as an airliner, so would get in the way quite a bit. And it would probably be swallowed up whole by the big sucky, spinny, noisy things hanging under the wings of (say) an A380 if I did get in the way. Add that to my list of things I'm allergic to.

For most of us, it isn't an option. London TMA is class A airspace which requires a valid instrument rating, but more importantly being in the vicinity of Gatwick, Heathrow, City, Southend, Luton and Stansted airports, in addition to smaller jet hubs such as Biggin, Oxford, Farnborough... There is considerable commercial traffic in the London TMA.

Ironically the largest GA-friendly country in the world (maybe second largest, not sure about Canada) has no such notion. I've never heard of regional QNH in the US. You pick up altimeter settings along the way. If you're VFR, you avoid the hard stuff by spotting it before it you hit it. If you're IFR, every controller you speak to will give you the appropriate value. No idea how they managed IFR before they had radios - that would be pretty much before I was born (which was NOT that recent).

Jan's comment is not strictly true. For example, right here where I'm sitting there are several different frequencies, under different authority, that I could be talking to, depending on altitude. Conceivably they could be giving different altimeter settings. Though it's most unlikely they'd differ by more than a small fraction of an inch (whatever that is in millibars).

Airbornestu regarding your post #21, I think you have a far greater understanding of the airspace over the UK than you give yourself credit for, notably your recognition that without an IR you can't operate in Class A airspace; not something that all pilots realise.

Do be mindful, however, that Class D is accessible to you in VFR (and under SVFR in certain conditions) and don't be afraid to ask. ATC should only refuse your proposal for their traffic reasons, but may need you to modify your routing on a tactical basis.

To get someone else of experience to cast an eye over your plans is a good idea. Whatever you do, enjoy the flying and always have an alternative plan in mind in case "Plan A" can't be achieved.

Do I have the correct understanding? That is, is some parts of the UK the local/regional/area QNH that is being set by pilots (received from an ATC unit) is the forecast QNH.

If true I find that a very unusual way of doing business. We all know how (in)accurate forecasts are.

TMAs in the UK are Class A airspace so you will need to file an IFR flight plan to enter.

In the UK, civil aircraft flying in Class G airspace below the transition altitude and not under a TMA would normally use a forecast RPS except when communicating with a civil ATC or AFIS unit who would give them a current observed QNH. If in communication with a military airfield, they would be given the QFE of that airfield but could request QNH. This may change (again) in the near future.
When a common transition altitude is agreed (hopefully) in the near future, forecast RPS will probably be discontinued.

It is not needlesly confusing if you look up the AIP. ENR 1.7 is clear on the OP question:

You seem to think that flying in the UK is difficult and confusing, when it is not.

If you ever visit, the CAA will not insist that you file a FPL for internal flights and that each flight is notified to them in advance by email, as the BCAA does when I fly my permit aircraft in Belgium.

It isn't... No... It is rather simple... Once you get But it is by no means as straight forward as I have experienced in many places in Europe, and NZ.

Literature provided by the UK CAA is abysmal at best! It is segregated, and very hard to find. For instance the Farnborough LARS guide that I posted, I have NO idea where to find it on the UK CAA's website (or NATS website - but really this is a PILOT GUIDE and should really be available on the CAA's website or the AIP in my mind).

If you look at NZ CAA, they actually publish a wealth of information for pilots, even print booklets and send them to ATOs to give their students for FREE! (yes I did say free). Have a look at: https://www.caa.govt.nz/safety-info/...tion-practice/ where they have a load of useful guides... Alongside a load of tuition aid / memos for all sorts of flying related items.

I really think that there is considerable room for improvement with how they organise both themselves (8 weeks to issue a licence is crazy) and their literature (or lack thereof) and mostly regulations (which nobody understands...)

I hope that one day overpaid management at the UK CAA will realise that they're not delivering the service that is expected from a "world leader".

Hear, hear!!

@alex90: thanks. But frankly, it has been quite long since I heard anybody hailing the UK as a world leader; more's the pity.

@Patowalker: what particularly annoys me is that, in the UK, two planes can be flying (outside controlled airspace), each doing their R/T with a different ground station (and perhaps with a different level of service, but I'll not even start about that). I hope this is a realistic example: one might be talking to Farnborough, the other to Brize Norton. So that the two of them, while doing the maximum possible effort in matters of communication, will not even be aware of one another's presence; except if told by the ground station they are tuned into - but these are under no obligation, and may well be too busy. Of course the pilots need to use their Mk1 eyeball anyway, there can always be nordo flyers around too. But in my part of the world, and in most, as far as I know, everybody flying OCAS will be on the one and only FIS frequency so that at least they hear what everybody is doing, and where.

That the UK sees a need to do as many things as differently as they can from the rest of Europe is less of a concern to me, basically; SERA is slowly taking care of that. And we should not expect everything to be the same as we are used to at home; indeed I must certainly admit my home country is less than exemplary on its rules for foreign Annex 2 aeroplanes. But, as said, the UK has a lot of room to make its rules of the air simpler, and more conform to the rest of the nearby world.

Regarding regional QNH settings: again, I am not for defending the system, and I am sorry if my words may have come across that way. But if anything is to be done about that anachronism, it will have to come from EASA.

Doesn't "OCAS" mean "outside controlled airspace" in your part of the world then? Do you have a requirement to be controlled when not in controlled airspace?

In the UK "OCAS" means what it says on the tin. There are various services offering varying degrees of help, but it's your choice which, if any, of them you feel like using, which may well be "none" if you, perfectly legitimately, don't have a radio, and may be "none" if you don't feel the need to talk to anyone. (Obviously various considerations of airmanship issues would come into such a decision, and personally I'm more likely to keep a listening watch on a relevant service than turn the radio off altogether.)

Yes, I must apologise for (for this once) relying on an acronym - I was actually trying to conform to forum habits ;)

Yes, I meant "outside controlled airspace", which is why I mentioned a Flight Information Service, too, and not a controller. Still, many pilots tune in, and offer position reports, so that one gets to know about a part of nearby traffic.

And yes, a listening watch is what I'll often do, too. As my craft is not transponder equipped, FIS can not do very much for me anyway, though they do have occasionally warned me of possibly conflicting traffic on the flimsy base of position reports, and perhaps primary radar - they were quite accurate!

Why would you expect to find a leaflet published by the company that provides Farnborough LARS on the CAA website? The AIP follows an international standard, so it could hardly be included there in its present format.

A comparison between CAAs is only fair if they are funded in the same way. The UK Government requires that CAA costs are met entirely from charges to those they provide a service to or regulate.

Jan,

It's not worth you getting annoyed about what happens in the UK, especially if you have no intention of flying here.
I believe you fly a Eurofox. Did you know over 80 have been sold in the UK?

Actually I fly an Apollo Fox, a Hungarian-built close cousin to the Eurofox. There's only a few obvious differences, the main gear track width and the door locks come to mind, but to the eye and to the pilot they are very very similar.

And yes I know there's a good many Eurofoxes in the UK, as there are a fair amount of C42's, which are more or less similar too, less similar in appearance but quite the same in performance and behaviour. Always surprising the Brits seem to have not created a local equivalent, or if they have then it is not flying in numbers. Or is that another misconception of mine? ;)

Southampton do an excellent 'glossy brochure' guide to flying in the vicinity of the Solent CTR/CTA.
By the way, the UK CAA do not provide ATS ('deliver a service'), that's up to Air Navigation Service Providers (ANSPs) who are regulated by the CAA

Thanks, I'll see if I can find a copy:ok:

Airbornestu,

I don't think there are any "jolly good reasons" for the London TMA being Class A - I think it's just the CAA's attitude towards GA and their inability to think "out of the box".

Los Angeles is a Class B zone but there are five VFR routes available in the area, including two that pass directly over the top of LAX:

1. The Mini Route from Santa Monica (SMO) to Hawthorne (HHR) at 2500', which requires a clearance from SMO or HHR towers as appropriate and then coordination with LAX tower.

2. The Los Angeles Special Flight Rules Area at 3500' or 4500' depending on direction. There is NO requirement for a clearance - you just set a listening squawk and make position reports on a dedicated frequency.

I've flown both routes and it is such a pleasure to fly with such minimal restrictions compared to UK airspace.

Here's the partially completed LAX Bradley International Terminal from 2500', southbound on the Mini Route:

http://i30.photobucket.com/albums/c3...ps5e5rq7mm.jpg

AOPA has an excellent page on how to fly VFR in the Los Angeles area:

https://www.aopa.org/advocacy/advoca...nsition-routes

142 just to clarify, was that pic of your pass over LAX taken with a handsome, well educated young chap at the helm ?

Please feel free to educate me! I am happy to learn. I can only respond to your question by another question: if not NATS's website, if not the CAA's website (who surely oversee NATS don't they?), and not the AIP's website (AIP stands for Aeronautical Information Publications - does it not? Is this not an aeronautical publication? [which the common person can understand without requiring further discussion with a lawyer!]) - where DO you find the guide? And more importantly, where do you find ALL guides for flying in these regions in one single place, reliably updated every time a change is made?

I entirely disagree with this statement. If a service is to be provided, the service should be taken like for like, irrespective of funding and/or politics which may or may not affect its provision, or any other single variable beyond the control of the customer. The single end goal of this SERVICE being provided, is to do just that, provide a service. If the service is good, you rate it so. If the service is bad, you rate it so. I received a licence within 2 weeks after I sent my application in NZ by post, in the UK I waited 8 weeks and they managed to damage my logbook to the extent of needing to getting it re-bound (twice). Why should you as a customer need to factor in any variable beyond your experience as a paying customer? (please enlighten me)

If funding is the issue - as you state - then it is the failure of the UK CAA to identify their funding problem and review their funding schemes. Why should all customers need to suffer and just accept inadmissible service?

anyway... rant over...

Really? Heathrow is now Class C iirc, but back when it was Class A to the ground, I flew through its edges on an SVFR clearance. As it happens I do have an IR, but since I was flying G-reg on an FAA license [sic] it would only count as an IMC rating, not an IR. I didn't get the impression it even occurred to anyone to think about it. And the heli route that goes right over the top of LHR predates the change to Class C. Presumably there was some kind of special exemption from the IR requirement if you were SVFR.

"Real" Class A (ICAO flavor, as - remarkably - implemented in FAA land) does indeed require an IR, but in the US it starts at FL180. There are glider pilots who have an IR for the sole purpose of being able to fly legally above 18000'.