MATZ QFE Altimeter Setting - Query

[Happy Wanderer]

Hi,

Some advice please from the guys in the know. . . .

I'm currently studying for my PPL and am taking my Nav exam tomorrow.

If on a x-country route you over-fly a MATZ at, say 4000ft, should the altimeter be automatically reset to the MATZ QFE, or should it be left on the relevant RPS?

Does the MATZ vertical altitude limit only come into play when proposing a MATZ penetration, ie given a vertical limit of 3000ft?

The above assumes that the MATZ vertical limit determines BOTH altimeter setting AND the need to establish radio contact - this may be a wrong assumption to make! - but clarification would be helpful.

Many thanks,

HW

[Widger]

Happy Wanderer,At 4000' you should probably be on a Flight level as you are above the transition altitude.If lower (below 3000') and you decide to penetrate the MATZ, the sensible thing would be to contact the operator of that MATZ and fly in accordance with their instructions. If possible you should remain on the RPS, and this should be the norm unless they require you to set the QFE to ensure separation aginst traffic within the MATZ. Once you are clear of the MATZ, RPS should once again be set.

[Pierre Argh]

A few gaps in the info given in the original question... You're not really asking for a MATZ Crossing at 4000ft, as in most if not all cases in the UK you'll be above the MATZ, so that doesn't count?

Is the NAVEX IFR or VFR? If the former then Widger is correct you should be flying at FL40 as it is above the TL for most areas in the UK?

I'll assume VFR, and that you'll be in Class G airspace... Radar service is not mandatory, but are you expecting to request one (which would have to be RIS as RAS is only available to IFR flights)... then the Controller will, probably, advise you on the setting they would prefer you to use (either QFE, QNH or RPS)?

if they don't, and you're unsure, then ask for confirmation? Under a FIS there's less of an issue, the Controller has no mandate to instruct you to fly on a setting if you cannot, or are unwilling to, comply (they might get a bit tetchy if you do refuse, it's really their problem but a polite rejection with a reason might smooth things down a bit)

IMHO your problem is much more likely to depend upon your instructor... (s)he will have their own ideas/opinions and would probably prefer to see you going along wth those...

[Happy Wanderer]

Hi there,

Many thanks for your replies here.

I think the problem is probably more straightforward than it first appears, but is actually based on an exam question in the 'PPL Confuser'.

I hope I'm not breaching any copyright issues, but the Q is as follows:

"After turning at Wolf Rock (lighthouse between The Scillies and Land's End), you accept a FIS from Culdrose LARS advising the controller that you plan to over-fly the St Mawgan MATZ at 4000ft. Your altitude west of the MATZ should be based on:
A - the St Mawgan QFE
B - the lower of the Scillies RPS and the Wessex RPS
C - the ST Mawgan QNH
D - the Scillies RPS"

The answer is given as D, with the following supporting comment:

"To the west of the St Mawgan MATZ, you should have your altimeter sub-scale set to the current Scillies RPS. Over-flight at 4000ft will position you above the MATZ, but as the Scillies/Wessex ASR boundary bisects the MATZ, so the Wessex RPS would have to be entered into your altimetr sub-scale as you cross the ASR boundary. (Note: If the controller at St Mawgan is very busy controlling other traffic in the St Mawgan area, Culdrose may ask you to free call St Mawgan to advise the controller there of your intentions. For the purpose of safe separation, you may be asked to use the St Mawgan QNH for transit over the St Mawgan MATZ)".

The reason I originally queried this is that I've seen other 'sources' suggest that the St Mawgan QFE should be set on the altimeter (ie answer A above), even though the flight takes you over/outside the vertical limit (3000ft) of the MATZ.

Getting this wrong could be the difference between passing and failing the Nav exam, and that's before consideration given to 'real flight' issues. . . .

Hope this clarifies.

HW

[Chilli Monster]

Yet another example of why we should get rid of this archaic slice of nonsense - why use RPS when you would have perfectly accurate and more relevant pressure settings (Both the Culdrose and the St Mawgan QNH's).

My preferred answer would be "C" - that way you would know your altitude relevant to obstacles in the area (the main reason for using an altimeter) AND it would tell you exactly how far above the St Mawgan MATZ you would be (4000ft - 3000ft - EGDG Aerodrome elevation).

[fireflybob]

Chilli Monster, I totally agree - the sooner we get rid of the RPS the better!

[DC10RealMan]

Fireflybob,

I wondered are you advocating getting rid of the RPS in total or just in the presented example?.

[Happy Wanderer]

Thanks for the responses (and interesting views!) on this. Even as a comparative novice, can see the sense in this.

Anyway, nothing cropped up on MATZs in yesterday's Nav exam, and I passed it.

Over and out.

HW

[Widger]

I am sorry, but the answer they gave you in the example is flawed...it states "If the controller at St Mawgan is very busy, well that is clearly an unlikely occurence!

[fireflybob]

DC10RealMan, it is somewhat tongue in cheek but I think the RPS is a hangover from the days of non radio aircraft which needed a "safe" altimeter setting to fly on, hence the fact it is available up to three hours ahead.

With the type of airspace and traffic densities we are now dealing with and the fact that most aircraft now have radio I think it is far more appropriate to fly on the QNH of a nearby aerodrome rather than an area QNH. By all means retain the RPS purely for reference for those days when you are flying over the foothills of Wales of the Trossacks in order to check terrain clearance.

I am aware that the UK military system is oriented to RPS for calculation of Transition Level and minimum levels for aerobatics and spinning etc but they also seem to insist on QFE too - whilst we are about it let's get rid of the QFE.

They seem to do quite well in the USA with just one "ALTIMETER" setting (ie aerodrome QNH) - they don't even call it by a Q code - when was the last time we used these? I would suggest that one altimeter setting used by all airspace users would be far safer and easier.

No doubt the supporters of QFE (and RPS) will come up with all sorts of reasons why that system is better!

[Widger]

fireflybob,The Crabs went to QNH some years ago, whilst the Senior Service said bugga that and stayed with QFE. It was not very long before the crabs saw the error of their ways and fell in line with the RN.Anyway, if you don't like QFE then don't fly to military airfields. I don't care what the septics do, they also eat Maccy D's every day, does not mean they are right. We, the British, invented flying in the first place!!! You will have us using inches next!!

[fireflybob]

Widger, I presume you prefer to fly on QFE, then?

[Widger]

No, I prefer to strap my arse firmly to the ground. 5000 hours on fixed and rotary chairs!