Lowest Regional QNH?

[Corporal Clott]

I haven't flashed around in a FJ for about 6 years now, but can anyone who is in current FJ flying practise tell me whether it is still standard procedure to set the lowest regional QNH for the route.

Some of you Valley types might be best to answer this.

It always dumbfounded me why we have so many regional QNHs for such a tiny set of islands - especially when you either set the lowest or the local airfield QNH. Most of my time on Tonka you'd use radalt anyway. In the US they just set the QNH of the airfield within 100miles of where they are flying - seems to work OK for them.

CPL Clott

[High_Expect]

Yes. Although the majority of Valley FJ also have RadAlt now :-)

[Pontius Navigator]

Regional gives you a safe backup regardless of terrain. Rad Alt is fine if you can see :)

As for setting airfield rather than regional it might be because of the small size of the island. Suppose Coningsby had one QNH and Waddington another? Which is better?

[LateArmLive]

Coningsby.

[SASless]

In the US they just set the QNH of the airfield within 100miles of where they are flying - seems to work OK for them.

As for setting airfield rather than regional it might be because of the small size of the island. Suppose Coningsby had one QNH and Waddington another? Which is better?


So KCLT and KPTI....50 or so miles apart...both International Airports....might have a different QNH....to what effect? How much variation do you think there might be....and what effect upon altitude conflicts would it have that would matter?

Add in Altimeter Error which my foggy memory tells me is limited to +/- 70 feet....and you still should not have a problem.

[Willard Whyte]

I always thought altitude was based on sheep's legs and cow's legs.

[Pontius Navigator]

SASLess, oh to have a nice uniform weather system with no local pressure variations. Lucky for you old chap. As our regional are quite small and quite large variations exist it is better to have everyone on the same pressure setting.

[BEagle]

The Regional Pressure Setting, isn't in effect a 'QNH' per se - it's a pressure datum value provided by the Met Office which has been tweaked slightly to assure that terrain avoidance will still be achieved within an entire ASR.

This whole topic is now under review as part of the ongoing Transition Altitude Harmonisation programme.

Hopefully this will result in fewer, but larger Altimeter Setting Areas.

[ShyTorque]

I always thought altitude was based on sheep's legs and cow's legs.

No, only the height of sheeps and cowses.

[SASless]

quite large variations exist

I accept having a single QNH setting might be a way of getting every one on the same QNH.....while enroute but conflict still exists once the Aerodrome QNH is used.

As we do not have such a concept as Regional QNH....limit ourselves to a Standard QNH once we go to Flight Levels....we do not have a problem.

When then does the UK insist upon a different system than we do?

If safety is the issue....which system is better and to what degree?

If there is scant difference in safety....which system is easier to use?

Now I do recall having fun teasing you folks about Altimeter Settings during a Missed Approach combined with a change in the Handling Pilot... and all that....so there must be something to the fact the UK system is far more complicated than it need be. Why else would there have been that mock BA Memo on the subject?

So I repeat the question.....how big a difference can there be between two Airport QNH settings within a hundred mile radius and does it present a real hazard to safe flight?

Come on PN....educate us on the dangers of doing away with the Regional QNH system....as the USA has done by never adopting such a concept.

[langleybaston]

Are we talking FOQNH here ....... forecast QNH?

If so, these were [are?] issued centrally, every hour, for [I think I recall] the following hour. The central forecast office produced them and they appeared routinely on the teleprinter broadcast, and were added to the observation by duty Met. for ATC .......... this in addition to the actual QNH for the airfield.

I might be wrong, it was a year or 20 ago!

Right now there is a Low in the Atlantic which comfortably manages 50 mb change at surface in 10 degrees latitude, so 1 degree latitude is worth 5 mb in that area, and so 120nm would give about 10mb difference in all the measures of pressure/altitude.

That would be worth some 300 feet in the vertical between the two stations ........ not that any flier sweating on a pension would wish to fly in said conditions.

Such lows have been known to cross the UK, as every M Fish knows.

[Brain Potter]

SASless,

Further examples of eccentric British military altimetry procedures:

1. Transition altitudes lower than MSA.

2. QFE.

3. "Clutch" QFE - requiring an approach to be flown using the QFE of a runway at a different aerodrome.

The defenders of these practices often say something like "it works well for us, why change it?", a point that has some validity but fails to acknowledge that standardisation with the rest of the world is a valuable objective that promotes safety and aids interoperability.

That said, the same argument can be levelled at using inches Hg instead of hPa.

[Pontius Navigator]

LB thank you for putting figures to my memory. Any thoughts on the typical pressure variations over similar distances in the US?

[Corporal Clott]

Thanks for the info folks. We have been debating the CAA's Transition Altitude piece and it would appear that the military wants to keep the myriad of ASRs - heaven knows why when it appears we still, and always have, set the lowest for this hour and the next!

As for UK experiencing more pressure variations than the US - ever heard of a hurricane? (and not the Hawker variety!).

Thanks again for all the input and for putting my mind at rest.

CPL Clott

[langleybaston]

Excluding a hurricane blundering inland, and of course setting a tornado aside as a very local crisis that only a pratt would knowingly approach, US gradients probably a bit less than the UK. I have in mind some nasty kinks in the isobars downwind of the Rockies, though!

There is also a latitude consideration in the extreme south of the States, in that large gradients just cannot build up anywhere near the Equator ......... Coriolis does not work, and, as fast as a Low is created, the surrounding air rushes in to fill it ........ like trying to dig a hole in dry sand.

Most UK forecasters never get to draw a chart much further south than 30N, and, when they have to, its a rude awakening. As for S hemisphere, I did consider standing on my head to make sense of the flows and the fronts, but even that didn't do it. My temporary job in CFO involved drawing ALL the S hemisphere at the end of a very long and no-chance-of-a-kip night shift.

YUURRRGGGGGH.

After 19 weeks I managed a dream posting out.

[DX Wombat]

Hopefully this will result in fewer, but larger Altimeter Setting Areas. From a civilian PPL point of view that would be good. For example, at the moment a flight from Halfpenny Green to Duxford involves two different QFEs (fair enough) but three different Regional Pressure settings and if you are brave enough to speak to a certain Midlands airport ATC you may, if they bother to let you know, get another one to work with. :\ I may be flying a dinky little C152 not a fast, shiny, noisy jet, but it still provides plenty to keep me occupied.

[Green Flash]

http://www.bristolairfield.co.uk/latcc_maps/EG_ENR_6_1_7_1_en.pdf

ASR's

[BEagle]

and it would appear that the military wants to keep the myriad of ASRs - heaven knows why when it appears we still, and always have, set the lowest for this hour and the next!

The military reps who attended the TA harmonisation workshop at Swanwick last November were certainly involved in the discussions. Regrettably one of them, in my personal opinion, displayed a 'fast jet knows best' mentality. Nevertheless, the MoD's concern is understood, although these days they are very much a minority airspace user. However, the Met Off are looking at statistical information concerning UK pressure gradient events in an effort to maximise the safe size of an altimeter setting area, commensurate with the provision of a safe pressure setting value.

[GOLF_BRAVO_ZULU]

If you are brave enough to speak to a certain Midlands airport ATC you may, if they bother to let you know, get another one to work with.

Presumably that's Elmdon Municipal who rather like us using their aerodrome QNH underneath their CTA? They do tend to assume everybody has read it off their ATIS. :}

[Pontius Navigator]

in an effort to maximise the safe size of an altimeter setting area, commensurate with the provision of a safe pressure setting value.

Areas which have been largely unchanged since the days of tooling around at 240 kts or less.

[SASless]

BP....oh please don't bring up the QFE thing.....that really is a bucket of worms.

There are a few Dino's here that just cannot fathom life without a QFE setting for an approach never minding it might not be for the runway being used as not all airfields are like billiard tables....flat and level.

Top that by reminding them there is no difference between an Altimeter reading "0" at landing compared to one that is indicating the field elevation in Feet MSL....and so forth and so on. Never mind the finger dance when one has to do a Missed approach...swapping from QFE to QNH, setting the third Altimeter to Regional QNH....and keeping it squared away as to which Altimeter is showing which setting all the while in the USA....we do the go around and do not have to touch the Altimeters at all.

But the old Denizens that lurk here will roll out and swear by all that is Holy that the UK system is the only way to do it for a host of reasons that do not hold water....other than it was good enough for Wellington.

[Pontius Navigator]

it was good enough for Wellington.

No, no, the Wellington not Wellington.:}

[GOLF_BRAVO_ZULU]

But the old Denizens that lurk here will roll out and swear by all that is Holy that the UK system is the only way to do it for a host of reasons that do not hold water

Not at all, dear boy. You foreign Johnies and ex colonials do it your way but please don't encourage the Europeans to bugger about with common sense; our way. I'm now intrigued to know, though, what manouvering area gradients you intrepid birdmen have to endure septicside.

[L J R]

...yeah SAS....and while we are on this issue, lets continue to discuss QFE Vs QNH again....
:ugh:

[Pontius Navigator]

LJR, was that in hectopascals or inches?

[DX Wombat]

Cubits and spans Pontius?
GBZ - how did you know? :rolleyes: It was someone from there who was, shall we say, rather unhelpful to me one day. I don't normally bother speaking to them (unlike EGOS to whom I will always talk) but on this occasion I was asked to contact them by the person sitting next to me. There was absolutely nothing wrong with my call (you will realise why in a moment) but the response was unwarranted. Unfortunately for the ATCO on the other end the person sitting next to me was the CFI who almost made a CFI-shaped dent in the top of the 152 but simply said to me "Carry on". I believe there was an interesting telephone conversation shortly after we landed.
Cheers Shawbury staff! You have always been very helpful and a pleasure to talk to . :ok:

[Easy Street]

Regrettably the RAF is represented at these kind of policy meetings by a community that has rarely operated outside the Barnsley ASR, and has even more rarely set 1013.2 mb because they spend all their time doing visual manoevering above TA with RPS set (a practice which inevitably leads to confusion and confliction with those pootling around at a FL). I speak of the crusty old Tutor / Tucano / JP / Jetstream QFI. They think us incapable of touching down at any altimeter reading other than 'zero'. I find it quite odd really, because in most areas CFS try to make things as difficult as possible (see "Tutor spin recovery technique"), so why we should all be mollycoddled when calculating our gate heights in the circuit, I have no idea. Hell, even UK civilian airfields offer QFE approaches to military aircraft in case the pilot's maths isn't up to much.

Meanwhile vast swathes of the front-line RAF have been operating for over 10 years into airfields at elevations such as 3300' (KAF), 2800' (Bastion), 1100' (Gioia), yada yada yada, not to mention all the North America experience gained at places like Nellis. Guess what, we use QNH and cope just fine, although I would rather that junior pilots had experienced QNH operations during their pilot training rather than on their first operational detachment. (Yes, we could demonstrate QNH operations at civilian or USAF airfields during pre-deployment training. No, that is not sensible use of expensive flying hours when it should have been done in a 22 Gp trainer). Time to come into line, I think.

Reform of the ASRs must address the issue of flight beneath CAS. I am puzzled that we teach people to fly around beneath CAS, the base altitude of which is defined (safely) using the QNH of the master airfield, whilst having a different (and usually lower) RPS on their altimeter. I know that avoidance of the ground takes precedence of avoidance of CAS, but setting the applicable airfield QNH would reduce airspace busts and would also mean that aircraft at the local SALT would be physically lower than if using RPS (and hence more likely to get VMC below). Win-win.

Finally. Whilst the UK might be able adopt a nationwide TA of 7000ft, I think we should go 'standard' on 18000ft. Whilst a lot of people operating in the 7000-18000ft bracket could not care less about their true height above ground, many operators do (notably FJ conducting ACT, strafe practice or aerobatics, all of which would typically be conducted using QNH despite being at 10-15000ft). An 18000ft TA can accommodate these operations without seriously affecting the safety of aircraft conducting long-distance cruise, the majority of which are above 18000ft. Those cruising below 18000ft are presumably flying aircraft with little enough performance that a few seconds to change QNH every hundred miles or so is hardly going to shatter the earth...

[BEagle]

I speak of the crusty old Tutor / Tucano / JP / Jetstream QFI.

Actually, it was a UK-centric FJ driver....

18000 ft is not the preferred TA as it would introduce a Transition Layer whch would lose cruising levels which are attractive to short range airline flights. In fact there is less enthusiasm for an 18000 ft TA across Europe than there is for maintaining the status quo.

10000 ft would similarly lose useful cruising levels for non-oxygen GA IFR operations.

6000 ft would both impinge upon the major London Airpoert holds and fail to offer the improvement sought by airlines for continuous climb profiles on the same altimter setting.

NATS has a preferred TA which seems a good compromise fro all concerned, requiring the use of 'area' altimeter settings in fewer, but larger altimeter setting areas. One hopes their valued research will not be subjected to spurious political eco-greenwash....

[SASless]

How does the USA make it work then Beags.....the East Coast is every bit as congested as Europe and the UK?

[BEagle]

Well, we were reliably informed that the US's 18000 ft TA is an historical legacy of the perceived need to have a single TA across the whole of the USA, including mountainous regions, from the days when Ernie Gann was flying the mails. This enabled safe terrain avoidance with due allowance for the altimetry and navigational errors of the day; but, given the opportunity to start again, they might prefer to use different TAs.

[SASless]

Don't forget the CCA...Continental Control Area....that has been done away with. Thus, perhaps, the FAA keeps the 18,000 foot level for a reason.

As Ernie Gann did his flying in the early days before O2 and pressurized cabins...the 18,000 foot level did not mean much to his flying. By the way Beags....Gann never flew the "Mails"....except that which was cargo on his Airline flights which in those days was a way of the government subsidizing the Airlines and getting Air Service into small cities and towns all across the country.

The advent of the DC2/3 series and its ability to transit the Rocky Mountains on one engine if need be....is what revolutionized the Airline industry.

Hell you should known Beags...you were there in the late 30's were you not?

[BEagle]

Hell you should known Beags...you were there in the late 30's were you not?

Ooh you rotten so-and-so! No I wasn't!

But I'm sure EKG flew DC4s later in his career? The wonderful story of the one which had a nigh-on triple engine failure on take-off makes great reading - as does the rest of his book. My 1961 original copy is a treasured item!

[SASless]

In order to be an Aviator....One must know Gann!

His books should be leather bound and passed down to new generations.

I also liked his story about the C-87 and the Taj Mahal and its near demise at his hands. The Taj and the C-87.

His account of flying over the Appalachian Mountains during a Cold Front passage in a DC-2 is so real....it gives me Goose Bumps. (Been there....done that too many times in comparable performing airplanes!).

As Beags so very rightly states....if you have not read Gann....DO!

[MaxReheat]

'standardisation with the rest of the world is a valuable objective that promotes safety and aids interoperability'......assuming, of course, that the 'rest of the world' are correct.:hmm:

[SASless]

In the scheme of the World's aviation operations....where would the UK rank?

You don't have a proper mountain in the realm (height wise) and yet you have the most complex Altimeter Setting procedures in the entire world....and you really think the rest of the World from Katmandu to Death Valley from just shy of the North Pole to the South Pole might just be doing it wrong?

Aw.....go on....pull the other one will you?

[Easy Street]

SASless,

Whilst I agree with your point, I wouldn't have picked Kathmandu as an example given the regularity with which metal meets mountainside around Nepal! :eek: