LARS units and regional QNH

[bookworm]

On a flight back from Cornwall back to Cambridge yesterday, I got the usual excellent service from a chain of LARS (and non-LARS) units. :ok: One minor event made me ponder altimeter setting procedures at Brize, though.

Over Oxford, approaching WCO at FL50, I wanted to descend to get beneath the Luton CTA. I asked specifically for the Brize QNH and said I was descending to altitude 3300 ft. In response I was given the Cotswold QNH and asked to report level at 3300 ft, which I duly did.

At WCO I was asked to freecall Luton, and on this particular occasion had no difficulty establishing contact and getting the Luton QNH, which was a good 8 mbar higher than the Cotswold. That, of course, put me above the 3500 ft base of the approaching Luton CTA. Even if Brize didn't have a London QNH, the Brize QNH would have been much closer than the Cotswold, which, as a forecast lowest QNH for a large region and a whole hour, is often significantly lower than the actual QNH. I have no doubt that the Brize controller was procedurally correct in asking me to fly on the Cotswold QNH, even though my procedure is to set a local QNH whenever possible.

So, can I choose my altimeter setting in class G -- though I appreciate it might make separation under RAS difficult -- and if not, what's the best way to handle such a situation?

[matspart3]

Need some military input here....

Brize do seem to have some funny ideas about altimetry outside CAS. When we prenote inbounds, they normally allocate a height based on their QFE. Transits either get Brize QFE or the Cotswold, but they always ask for our QNH for inbounds. I'm guessing it's Unit specific procedures?

As far as I'm concerned you can use whatever setting you like in Class G, that is appropriate to your flight and I'm not entirely comfortable with the 'climb/descend and report level..xxx ft, on xxx mb' military phraseology under anything other than a RAS, but that's a whole other can of worms!!

In the situation you describe, I would have asked for the London QNH.

Notwithstanding the above, Brize do an excellent job with limited resources

[Chilli Monster]

So, can I choose my altimeter setting in class G -- though I appreciate it might make separation under RAS difficult -- and if not, what's the best way to handle such a situation?

The Brize Controller, although not at fault, should have had a little bit more airspace awareness.

Yes - you can choose what you fly on, especially in that scenario. I would have re-iterated your request, giving in as few words as possible why you wanted it. You could probably have asked for the London, as I believe Brize might hold that for exactly the reason you wanted it - that might have been a bit of a prompt to the ATCO. If you had bust CAS because of this then it would have been an interesting debate as to who would have been at fault.

Yet another reason why Regional Pressure Setting (It hasn't been technically called the Regional QNH for a while) should be shown the door.

[2 sheds]

Even the Brize QNH would have been better than nothing, pending obtaining a LTMA QNH.

It would be a great advance to flight safety if RPS were kicked into touch (apart from certain specific areas, perhaps - the middle of Wales, Scottish highlands, North Sea) - and the military stopped this ludicrous obsession with QFE reference outside the immediate circuit area.

[bookworm]

Notwithstanding the above, Brize do an excellent job with limited resources

I strongly agree. I guess the main thrust of my original post was along the lines of

It would be a great advance to flight safety if RPS were kicked into touch

Actually, kicked out of the stadium, perhaps... ;)

[vapourer]

Hesitate to get involved in the regional pressure setting dog's dinner but the plain fact is that the airspace beneath TMAs and CTAs, except airways and Daventry and Worthing CTAs, does not form part of the Altimeter Setting Region system and pilots should use the QNH of an adjacent aerodrome. Therefore in my opinion the person who would be responsible for an unauthorised excursion into CAS by an aircraft flying on the RPS is the pilot.

In fact back in the late 80s early 90s there were a couple of Airproxes caused by military aircraft aborting low-level missions and climbing into controlled airspace whilst using the RPS because they had no means of obtaining a local QNH. As far as I know this particular issue has never been satisfactorily addressed despite CAA Recommendations to the MOD at the time, although I stand to be corrected.

[CAP493]

vapourer is absolutely correct.

Golden Rule = never never use anything other than a local QNH when operating below any controlled airspace (CAS) the base of which is defined as an altitude. In all cases the altitude concerned will give you a clue as to the local Transition Altitude which could well be above 3000 feet.

Irrespective of whatever pressure setting you are given by any ATC unit, if you're operating below CAS where the base is an altitude, set a local QNH to avoid infringing it because the RPS will always be lower than the actual QNH and so if you use it, you'll actually be higher than your altimeter indicates.

:ok:

[Spitoon]

The key to all this is understanding what the various pressure settings mean and what they can or should be used for. RPS is for assuring terrain clearance whilst a local QNH is more useful for avoiding airspace or for ATC to separate traffic in the area. The bottom line is that the pilot should use the most appropriate pressure setting(s) unless specifically instructed to use a different setting by ATC. The real problem arises when you're trying to avoid terrain and airspace at the same time!!

[aluminium persuader]

We (military ATC, not a LARS unit but near as dammit!) have recently changed our procedures & no longer issue a regional unless specifically asked for. We're near lots of CAS & the local QNH is so much more accurate.

ap.

[2 sheds]

Well done, sir. One down, one to go (QFE)!

2s

[Standard Noise]

If a pilot wants the RPS so be it. Doesn't make a blind bit of difference to me as long as I know which setting he's on.

[chevvron]

I seem to remember that when the military abandoned their 'QNH only' procedures, they also abolished local QNH; departures were supposed to change from QFE to SPS on climbout and vice versa on descent; if staying below transition altitude, only RPS was to be used. Of course this meant that Northolt, Benson and Odiham, being in or below the LTMA, had to operate non-standard, which met a lot of resistance especially with new controllers straight from Shawbury!!
Never did get a reasonable explanation why the military chose to revert to using QFE, especially as the change was very poorly notified, whereas the change to QNH procedures was well planned and executed, with the excellent Dave Harrison visiting most units to brief them. I WAS told it was because an 'elderly gentleman' (senior officer to those unfamiliar) cocked it up one day on a check ride thinking he was on QFE and trying to descend to zero on his altimeter, but that was only a rumour.

[Pierre Argh]

Never did get a reasonable explanation why the military chose to revert to using QFE, especially as the change was very poorly notified, whereas the change to QNH procedures was well planned and executed, with the excellent Dave Harrison visiting most units to brief them. I WAS told it was because an 'elderly gentleman' (senior officer to those unfamiliar) cocked it up one day on a check ride thinking he was on QFE and trying to descend to zero on his altimeter, but that was only a rumour.
IIRC it was a large lobby of Transport pilots who pressed for the introduction of QNH, that was ignored by a silent majority... until it was introduced and then a vociferous bunch of FJ pilots stood up (probably inc the senior gent mentioned) and demanded a reversal on the grounds of flight safety.

The RAF introduced the change without reference to the RN, pushing ahead with an ammendment to Military Flying Regulations... which as you can imagine didn't go down well.

IMHO the snag was a making an attempt to switch from one pressure setting with the total exclusion of the other that casued many snags. The effect of this Cock-up has had a lingering effect, even mention QNH anywhere near STC these days and they'll cry foul citing this badly managed/considered event

back to the subject of the original post... one of the problems of RPS is that its a forecast lowest pressure acroos the region... some of these are large, so for example when there's a massive Low in one corner the difference between RPS and QNH in the opposite corner (and indeed between adjacent RPSs) can be significant.

[2 sheds]

If a pilot wants the RPS so be it. Doesn't make a blind bit of difference to me as long as I know which setting he's on.

There is, however, a small matter of verifying the Mode C !

[tmmorris]

Benson do the same thing - blindly give RPS regardless of the circumstances. I've often departed from Benson for CPT and been given the RPS, and virtually had to go to 'words twice' to explain that actually I would be climbing to and maintaining my chosen altitude on the LONDON QNH to avoid busting CAS at Compton; though at least Benson do quote the Lon QNH on their ATIS.

T

[dolphinops]

Transiting in the local area you'd get the RPS (and for the next area as you leave cos I'm good like that)
Transiting the MATZ 3000' or less and you should be politely requested or politely instructed:p to set the QFE.
This is primarily to make coordinating departing or Radar pattern traffic a damn sight quicker and safer for all concerned.
If you want to stay on RPS fine by me. Just keep a good look out :ok:
That's notwithstanding CAS concerns. I don't have that snag.

[Standard Noise]

There is, however, a small matter of verifying the Mode C !
Which doesn't matter too much unless you're using it for separation purposes.

[2 sheds]

WHAT....?!!

[Il Duce]

"...unless you're using it for separation purposes"!!!????
As opposed to, perhaps, using it for cooking purposes or medical purposes?

[neilmac]

I am guessing the Brize controller wasnt busy so by giving you the Cotswold and not his QNH/QFE to transit his Zone, thus saving you another pressure change on leaving. In that area I believe you are in the Cotswold RPS? So at WCO change to Luton and get either their QNH or London RPS. Its not really an awareness problem whey should a BZN controller worry about your altitude on crossing the Luton CTZ? In a GA plane WCO to edge of Luton zone is plenty of time to adjust if you give Luton an early call.
Benson usually give the Cotswold when tracking towards CPT because 8/10 times in previous experience pilots GH to the west of CPT in the Cotswold RPS area! To the east of CPT they will give you the London RPS or at least I would expect them to. QFE when flying next to mil aerodromes helps co-ordinate you against IFR traffic inbound. Our Mode C readout is always based on 1013 so at least with a/c on QFE its easy to work out internal co-odrination rather then a long winded call right so your on the Cotswold im on QFE .....waiting to work out differerences do I have enough separation when your planes are getting closer! Most of the time its pretty easy but when your busy it helps. Im off for a ly down pressure questions do that to me!
Happy Flying

NM

[chevvron]

Brize always use the Cotswold RPS rather than their own QNH; at least they do when they hand traffic to adjacent LARS units.
Mode C is transmitted from the aircraft on 1013 but it's displayed on ATC radars based on whatever pressure setting you input, the conversion being done by each individual units processor. I know Lyneham used to input 1013, but other RAF units usually input QFE, whilst civil units input their own QNH.
There is no such thing as the 'London RPS'; Benson should issue their own QNH as the QNH of any airfield under a TMA is deemed to be the same as any other airfield under that TMA.

[Chilli Monster]

I am guessing the Brize controller wasnt busy so by giving you the Cotswold and not his QNH/QFE to transit his Zone, thus saving you another pressure change on leaving.
Get rid of the RPS - that would save the problem.
In that area I believe you are in the Cotswold RPS?See point above So at WCO change to Luton and get either their QNH or London RPS.
As has been said before - there is no London RPS.

Bookworm said on this occasion he was able to get the Luton QNH - what if he hadn't been able to? Would the Brize Controller still blindly given the Cotswold or would he have had an attack of common sense in giving what he was actualy asked for?
Its not really an awareness problem whey should a BZN controller worry about your altitude on crossing the Luton CTZ?
My - that's a professional attitude. I'm all right jack, stuff the big picture. (And I would certainly be concerned if I had somebody pointing underneath somebody else's CTA - read the original question)
In a GA plane WCO to edge of Luton zone is plenty of time to adjust if you give Luton an early call.
I fly a GA aircraft that does 220Kts - do you reckon? Also see comment above about actualy getting the call in.
Our Mode C readout is always based on 1013
So how do you validate Mode 'C'?
so at least with a/c on QFE its easy to work out internal co-odrination rather then a long winded call right so your on the Cotswold im on QFE .....waiting to work out differerences do I have enough separation when your planes are getting closer! You could always do it the way the civil world does - one Controller, one bit of airspace ;) Cuts down on that nonsensical co-ordination.

[bookworm]

I am guessing the Brize controller wasnt busy so by giving you the Cotswold and not his QNH/QFE to transit his Zone, thus saving you another pressure change on leaving.

I didn't enter the Brize CTR. I specifically waited until I had passed the edge of the zone before descending from FL50, to save him coordination with Brize Zone.

So at WCO change to Luton and get either their QNH or London RPS. Its not really an awareness problem why should a BZN controller worry about your altitude on crossing the Luton CTZ?

Why? Because we're all interested in flight safety and avoiding airspace busts.

Don't get me wrong -- I asked just once for the Brize QNH: I certainly could have been more assertive in asking for a real QNH. And I made contact with Luton in good time. But I was specifically aware of the issue on this, a fairly quiet day with not much else to worry about. No hazard in this case, but I wanted to raise awareness of the issue.

[neilmac]

Sorry, of course there is no London RPS my error. Chilli monster u have a PM.

[Standard Noise]

"...unless you're using it for separation purposes"!!!????
As opposed to, perhaps, using it for cooking purposes or medical purposes?
IL Duce & 2SHEDS- If I have 2 vfr a/c both on a RIS, I tend not to give them standard separation, only traffic info after all it's an 'information' service. But I will want to know their respective altitudes which I am capable of working out from the pressure setting they are on. Maybe you both spend your time separating everything, personally, I don't!

[flower]

There certainly was a section in MATS part 1 that said the RPS should not be given unless requested by the pilot or words to that effect, haven't checked to see if it is still there.

[Irv]

I ws amazed that one of my 'intro to the uk' pilots was given the RPS (Portland) by Bournemouth LARS whilst we were in the 'New Forest Tunnel' - the class G between Southampton and Bournemouth with the Solent 2000' cap on it - despite reporting near Beaulieu! (I had already briefed him on RPS with warnings not to use it under CAS, but I'm pretty sure he would still have set it if I hadn't been there to question it.
ps: thanks JS for the pointer to this post from trhe forum atfly on track (http://www.flyontrack.co.uk)

[2 sheds]

IL Duce & 2SHEDS- If I have 2 vfr a/c both on a RIS, I tend not to give them standard separation, only traffic info after all it's an 'information' service. But I will want to know their respective altitudes which I am capable of working out from the pressure setting they are on. Maybe you both spend your time separating everything, personally, I don't!

The point is - how do you verify Mode C of an aircraft at an altitude if you do not ascertain that the pilot is reporting altitude based on a common reference? Surely you would, as a norm, have the aerodrome QNH set on the radar for aircraft below the transition altitude? (Apart from military units, which probably use Timbuktu QFE). I get the impression that you are saying that you will accept a level report based on any old setting and make a mental calculation to decide if it is within tolerance. Very professional - what conversion are you using, do you correct it for temperature and pressure, who has authorised that procedure, and what chance is there of you making an error if the Mode C is out of tolerance and you are busy? Furthermore, if you then use the Mode C for traffic information, it is likely to confuse the situation ("traffic at altitude 2700 ft" - pilot thinks "no, I'm at 2400 ft on the RPS").

It is quite evident from all the foregoing correspondence that in the context of most traffic at and below the transition level that is going from one aerodrome-based ATC unit to another for service, use of an RPS is not only a waste of time but confusing and potentially hazardous. It has its uses for low level traffic - military tactical, pipeline patrols etc - apart from that, it is a menace and should be limited to the lumpy bits of Wales and Scotland and the sea areas.

[Spitoon]

I'm with Standard Noise on this. If the aircraft are getting a RIS they get information not separation. If the information includes a level based on unverified Mode C then that's what I'll tell the pilot. I get the impression that you are saying that you will accept a level report based on any old setting and make a mental calculation to decide if it is within tolerance. Very professional - what conversion are you using, do you correct it for temperature and pressure, who has authorised that procedure, and what chance is there of you making an error if the Mode C is out of tolerance and you are busy?Conversion factors, temperature and pressure corrections?? Get real. It's to do with providing the service that I have agreed with the pilot, not overcontrolling and separating every VFR pilot and his dog. And, by the way, just as you say, I take a pride in doing it very professionally.

[rodan]

I get the impression that you are saying that you will accept a level report based on any old setting and make a mental calculation to decide if it is within tolerance. Very professional - what conversion are you using, do you correct it for temperature and pressure,
I find 30' per millibar, the way I was taught, works just dandy. You cannot force a pilot to fly on your QNH in class G just because it makes it easier for you.

who has authorised that procedure,
Are you serious? Mental arithmetic should be an authorised procedure now?

and what chance is there of you making an error if the Mode C is out of tolerance and you are busy?
Practice seems to alleviate the risk.

[ShyTorque]

Bookworm,

The Luton QNH is available via their ATIS. The London QNH is broadcast on the Heathrow ATIS frequency and on all of the London area VOR idents, if your NAV box has a voice facility. :)

We use our second VHF box to keep up to speed on the relevant local QNH via ATIS. We try to have the relevant QNH set before we call the ATC unit to which it belongs, so our altitude is immediately comparable to that of other aircraft they are working. We don't use RPS unless nothing more accurate is available, such as more than 25 nms away from an ATC unit and heading for the hills.

Had you "bust" airspace it is your good self, as the pilot in command, who would be found primarily at fault.

However, a second call to Brize, requesting the London QNH would surely have solved your dilemma? ;)

[055166k]

UK AIP ENR 1.7
Altimeter Setting Procedures

3.9 Airspace within all Control Zones [ CTRs], and within and below all Terminal Control Areas [TMAs], Control Areas [CTAs] except Airways and the Daventry and Worthing Control Areas, during their notified hours of operation, do not form part of the ASR Regional Pressure Setting system.

3.10 When flying in Airspace belowTMAs and CTAs detailed above, pilots should use the QNH of an adjacent aerodrome when flying below the Transition Altitude. It may be assumed that for aerodromes located beneath such Areas, the differences in the QNH values are insignificant. When flying beneath Airways whose base levels are expressed as Altitudes pilots are recommended to use the QNH of adjacent aerodrome in order to avoid penetrating the base of Controlled Airspace.

[2 sheds]

I'm with Standard Noise on this. If the aircraft are getting a RIS they get information not separation. If the information includes a level based on unverified Mode C then that's what I'll tell the pilot. Conversion factors, temperature and pressure corrections?? Get real. It's to do with providing the service that I have agreed with the pilot, not overcontrolling and separating every VFR pilot and his dog. And, by the way, just as you say, I take a pride in doing it very professionally.

I don't know how the subjects of separation or over-controlling or type of service came into the disussion! Are you now saying that you would identify an aircraft with a discrete Mode A code but leave the Mode C unverified?

[ToweringCu]

You can request and should receive any pressures the unit has. However, you should have been flying on the RPS not the Brize qnh. The controller probably thought that you meant to ask for the RPS.

[chevvron]

2 Sheds- at my unit SRG insist that if you issue a discrete transponder code to an aircraft to identify it, you MUST verify any associated mode C.

Towering Cu- it could be that RAF units don't even have access to local QNH as they tend to use QFE below TA and 1013 above it, hence for crossing the Brize Zone you would normally be asked to set Brize QFE, and outside the zone below TA you would be given the Cotswold regional; hopefully someone from Brize will pick this up and either confirm or refute!

I would personally suggest that if flying in class G below TA and NOT talking to ATC, you use RPS; if talking to ATC you use the observed QNH they give you.(But be warned some tower only ATC units plus FISO units with no qualified met observer may only be able to issue QFE!)

[ShyTorque]

I would personally suggest that if flying in class G below TA and NOT talking to ATC, you use RPS; if talking to ATC you use the observed QNH they give you.(But be warned some tower only ATC units plus FISO units with no qualified met observer may only be able to issue QFE!)

Chevvron, although use of RPS helps to guarantee (a bit extra) terrain clearance during cruise or descent, in a decreasing barometric pressure weather system, the use of it during a climb is likely to lead a pilot to bust into controlled airspace above. The airspace over the Pennines to the east of Manchester is a good example of where this might happen. From that point of view, it is better (for the security of one's pilot licence) to use the local QNH when climbing.

[Il Duce]

I don't know how the subjects of separation or over-controlling or type of service came into the disussion! Are you now saying that you would identify an aircraft with a discrete Mode A code but leave the Mode C unverified?

Good point, well put. My point was, exactly the same as Standard Noise, that under a RIS I provide the pilots with information so that they can sort out their own separation. That information is greatly enhanced if I know what pressure setting the conflicting aircraft has set and his height/altitude.

Going back to bookworm's original question - I was under the impression (please feel free to alter that impression) that a pilot could request any pressure setting he wished but set whatever the controller told him to depending on the aircraft's proximity to MATZs, active radar patterns, CAS etc etc.
I'm all for letting the flying fraternity getting on with what they want to do without overdoing it with altimeter changes every 2 minutes. Overcontrolling - no thanks, I don't get paid enough for the amount of controlling I do now so I'm not going to provide unpaid overtime as well!

[Pierre Argh]

Applying separation under RIS... there is of course one ocassion when the Controller should take standard separation into account, and that's when vectoring a/c under RIS. The pilot would be quite entitled to be pissed off if the Controller's vector placed the aircraft into confliction, unless the pilot had been visual beforehand. An opinion that is IIRC backed up by several Airprox Reports?

But I digress?

[2 sheds]

2 Sheds- at my unit SRG insist that if you issue a discrete transponder code to an aircraft to identify it, you MUST verify any associated mode C.


Yes, that was the point that I was making - another unit has the right to assume that the associated Mode C of a discrete code has been verified if it is not de-selected pronto.

The other point:

MATS Pt 1:
Controllers are to verify the accuracy of Mode C data, once the aircraft has been identified and the Mode A validated, by checking that the readout indicates 200 feet or less from the level reported by the pilot.

"Readout", not a rapid rough calculation because the pilot is reporting on a different subscale setting.

[anotherthing]

Can't be bothered to read all of the posts as it is getting rather silly... however (and their are some exceptions to the rules, both individuals and units).... the majority of NATS controllers do not know how to effectively apply RAS/RIS - and the college instructors are amongst the worst.....

Maybe this lack of knowledge (or ignorance to use the word in its proper definition) is one of the reasons why military and civil do not always understand each other...

I will now step back from the fuse I have lit, but suffice to say, I have extensive knowledge of both sides of the operation..

:E

[Spitoon]

I don't know how the subjects of separation or over-controlling or type of service came into the disussion! Are you now saying that you would identify an aircraft with a discrete Mode A code but leave the Mode C unverified?Who said anything about identifying an aircraft or not verifying the mode C associated with a discrete mode A code????

If the aircraft will be with me for only a short while - or if there are only a few aircraft about - and I can ident it using another method, I'll happily allow it to stay on 7000 and give it and others info. Skills such as maintaining an ident without a discrete SSR code seem to be alien to many controllers these days!!

[2 sheds]

Spitoon

1. It was implied by a previous correspondent.

2. Quite agree!

2 s