Regional QNH or 1013

[Driver6452]

Hi there, could anyone advise me on this one, planning a couple of flights above the transition level circa 5000 ft or FL 50, in uncontrolled airspace, and for terrain clearance I`m not sure what altimeter setting to use as were not planning to fly the quadrantal rules, the flights will be conducted VFR, asked some flight instructors and pilots with many more hours than me and the results are equal, also in the Trevor Thom manuals it states that if you have various headings use regional QNH, so any advice would be much appreciated thanks in advance.

[airac]

just watchout for the base of CAS it could be altitude or FL.
At 5000' I doubt you'll hit any terra firma

[Genghis the Engineer]

Above transition level (certainly above FL50 in the UK), I'd use QNE (1013) for traffic avoidance. Below TL, I'd use RPS (regional pressure setting, commonly but slightly incorrectly called regional QNH) for terrain avoidance.

And talk to ATC and make sure they know what setting you're using.

G

[BackPacker]

Is this a troll?

Above the transition layer you use 1013, below it you use the RPS for FL/altitude reporting. Simple really. The only variable is the altitude of the TL itself. And the RPS of course.

The quadrantal rule (or semi-circular rule) is formulated so that it uses altitudes (thus based on the RPS) below the TL, and uses FLs (thus based on 1013) above. Same goes for the vertical limitations of CAS.

At 5000' I doubt you'll hit any terra firma

I'm searching for an example where there is terrain that extends through the TA into the Flight Levels, and which would make a re-calculation of that terrain altitude to its corresponding FL necessary to stay safe. Does anyone know of such an example?

[englishal]

You don't have to use FL if VFR but I always do because most of the class A airspace (airways etc.) are normally a FL so it ensures you won't bust them. I'd always plan to try and fly at FL50 or above on a reasonably long x/c because you have less traffic to worry about up there and comms / radar are better. I'd always aim to fly a quadrantal level but sometimes that isn't possible due to the weird class A airways in the UK.

The TA is normally choses at an alt above the highest terrain around, so in the USA is is 18,000. IN the UK not much extends above 3000', though I reckon it would be sensible for Europe to have one common TA which is based upon the highest of the Alps.

[BackPacker]

You don't have to use FL if VFR

What you probably mean is "you don't have to fly at a rounded FL according to the quadrantal/semi-circular rule" if VFR.

But as far as I know you have to use flight levels in your reporting to ATC, if you're above the TL. I mean, you don't want to leave the mental arithmatic to the controller, do you?

"G-ABCD report altitude" "6200 feet QNH 1003 G-CD"
"G-DEFG report altitude" "FL65 G-FG"

Now is there a conflict or not? (And what's more important: How many seconds did it take you before you found the answer?)

[IO540]

Worth mentioning that most pilots don't actually care about any of the above, with the main objective being to keep out of controlled airspace

So if flying below CAS whose base is defined as a flight level, you fly on 1013.

If flying below CAS whose base is defined as altitude, you fly on the actual QNH, but that gets a little tricky because the regional pressure setting is no good for staying below CAS. The "proper way" to stay below CAS whose base is defined as an altitude is to obtain the QNH from the ATC unit responsible for that piece of CAS (which you can do by calling it up, or by dialling up its ATIS).

[BackPacker]

Or you do as I do when doing aerobatics between 3000' (below the TA) and FL 55 (above the TL): Leave the altimeter on QNH and use the transponder to see what FL you're at (has to be a mode C or S, obviously).

(My usual aerobatics location has several layers of CAS so I run the risk of busting both below and above.)

[DB6]

Personally I find regional QNH to be fairly useless. If you don't want to use 1013 - and I don't bother if I'm just farting around aka enjoying flying - then I would recommend using the QNH of any airfield near your track (within 25nm if you want to be correct), and I would further recommend using ATIS broadcasts to get them as you don't have to bother making R/T calls then.

[Cusco]

If you're squawking 7000 Mode C (as you do, don't you?) your altitude on the radar controller's screen will be based on FL/1013, so it makes eminent good sense if you're above TL whether you're farting about or not to use FL /1013 on your altimeter.

Cusco

[MFC_Fly]

BackPacker wrote:

But as far as I know you have to use flight levels in your reporting to ATC, if you're above the TL. I mean, you don't want to leave the mental arithmatic to the controller, do you?

"G-ABCD report altitude" "6200 feet QNH 1003 G-CD"
"G-DEFG report altitude" "FL65 G-FG"

Now is there a conflict or not?

Well since the controller in your example requested the pilot to report the aircraft ALTITUDE then G-CD responded correctly and G-FG didn't and was therefore the cause of any confusion

[MFC_Fly]

DB6 wrote:

Personally I find regional QNH to be fairly useless. If you don't want to use 1013 - and I don't bother if I'm just farting around aka enjoying flying - then I would recommend using the QNH of any airfield near your track (within 25nm if you want to be correct), and I would further recommend using ATIS broadcasts to get them as you don't have to bother making R/T calls then.

And if there are no other airfields within 25nm of your track and there is high terrain that extends above the 3000' TA? RPS (or Regional QNH as you call it) does have its uses in some UK locations a little further north than where you are.

[Human Factor]

I'm searching for an example where there is terrain that extends through the TA into the Flight Levels, and which would make a re-calculation of that terrain altitude to its corresponding FL necessary to stay safe. Does anyone know of such an example?

Plenty around the world. None in the UK AFAIK.

[reportyourlevel]

The airport I work (UK) at has a transition altitude of 3000' and an MSA of 3200' in one sector - is that what you mean?

[Talkdownman]

Originally Posted by Genghis the Engineer

Above transition level (certainly above FL50 in the UK), I'd use QNE (1013) for traffic avoidance. Below TL, I'd use RPS (regional pressure setting, commonly but slightly incorrectly called regional QNH) for terrain avoidance.

QNE, slightly incorrectly called 1013...

QNE is not a pressure setting. QNE is the reading in feet on an altimeter with the sub-scale set to 1013.2 mb when the aircraft is at aerodrome or touchdown elevation. During conditions of exceptionally low atmospheric pressure it is not possible to set QFE or QNH on some aircraft altimeters. In these circumstances an aerodrome or runway QNE can be requested.

1013.2 is the Standard Pressure Setting. Flight Levels are measured with reference to the standard pressure setting of 1013.2 mb. In the UK, consecutive Flight Levels above the transition level are separated by pressure intervals corresponding to 500 ft; at and above FL200, by pressure intervals corresponding to 1000 ft.

The Regional Pressure Setting is a forecast of the lowest QNH value within an ASR. The values which are made available hourly for the period H + 1 to H + 2, are given in whole millibars.

UK Altimeter Setting Procedures are here.

Originally Posted by Cusco

If you're squawking 7000 Mode C (as you do, don't you?) your altitude on the radar controller's screen will be based on FL/1013, so it makes eminent good sense if you're above TL whether you're farting about or not to use FL /1013 on your altimeter.

The aircraft altitude encoder transmits Mode C data based on Standard Pressure Setting 1013.2. The radar processors will convert the readout to indicate altitude or flight level depending on the Transition Altitude and the QNH entered into the radar data processors.

[mrmum]

UK terrain above TA/TL

I'm searching for an example where there is terrain that extends through the TA into the Flight Levels, and which would make a re-calculation of that terrain altitude to its corresponding FL necessary to stay safe. Does anyone know of such an example?

Plenty around the world. None in the UK AFAIK.

Don't have a chart to hand, but as in UK airspace the transition altitude outside CAS is 3000', doesn't that make a lot of Scotland (outwith the Scottish TMA and Aberdeen CTR/CTA), bits of the Lake district and possibly Wales fit the bill. As for calculating altitude-FL's, isn't that why we have two altimeters in situations when we can't see the ground coming.

[soaringhigh650]

in UK airspace the transition altitude outside CAS is 3000'

What if you're OCAS below a CAS shelf? Is it still 3000 feet?

[Talkdownman]

Originally Posted by soaringhigh650

What if you're OCAS below a CAS shelf? Is it still 3000 feet?

If below a TMA the TA is the TMA TA eg. London TMA TA 6000ft London QNH
Ref in UK AIP somewhere.

[mrmum]

TA outside CAS

Originally Posted by soaringhigh650
What if you're OCAS below a CAS shelf? Is it still 3000 feet?

Okay, by outside I should have specified outside laterally, not below a shelf

UK AIP (11 Feb 10) ENR 1-7-1 Civil Aviation Authority AMDT 2/10 ENR 1.7 — ALTIMETER SETTING PROCEDURES
1 Notification
1.1 The Selected Transition Altitudes listed in paragraph 4 are notified for the purposes of Rule 34 of the Rules of the Air
Regulations 2007.

3 General Procedures
3.1 The Transition Altitude within the UK is 3000 ft except in, or beneath, that Airspace specified at paragraph 4.1.

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 below TMAs 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 an adjacent aerodrome in order to avoid penetrating the base of Controlled Airspace.

4 Selected Transition Altitudes
4.1 The following Transition Altitudes apply to flights within or beneath the following Airspace:

Aberdeen CTR/CTA 6000 ft
Belfast CTR/TMA 6000 ft
Birmingham CTR/CTA 4000 ft
Bristol CTR/CTA 6000 ft
Cardiff CTR/CTA 6000 ft
Doncaster Sheffield CTR/CTA 5000 ft
Durham Tees Valley CTR/CTA 6000 ft †
East Midlands CTR/CTA 4000 ft
Edinburgh CTR/CTA 6000 ft
Glasgow CTR/CTA 6000 ft
Leeds Bradford CTR/CTA 5000 ft †
London TMA 6000 ft
Manchester TMA 5000 ft
Newcastle CTR/CTA 6000 ft
Scottish TMA 6000 ft
Solent CTA 6000 ft †
Sumburgh CTR/CTA 6000 ft †

† Note: Outside the notified hours of operation the Transition Altitude is 3000 ft.

[soaringhigh650]

This is horribly complicated and potentially dangerous too.

There needs to be a common TA.