Transition Layer - Not Required

[karrank]

Interesting thread elsewhere: FL180/18000FT (http://www.pprune.org/forums/showthread.php?s=&threadid=140522)

I gather from this we are being needlessly restrictive by locking up the level between 10,000FT and FL110?

And non-compliant...

[farqueue]

Hopefully not many fly in the band from 10,000' down to FL110!

(think!)

[Spodman]

If you had access to a radar you could see the occasional 1200 at 10,500. I've always assumed it was crook mode C. :rolleyes: You are right though, cruising is not permitted at 10,500 but I don't see why it shouldn't be.

If a VFR aircraft at 8,500 can be overflown safely by an IFR at 9,000, then why can't a VFR at 10,500 be overflown safely at FL110? The concept is that IFR can be 500FT from a VFR, and it applies at both levels.

If (given the altimetry limitation <1013HPA) two IFR can pass at 10,000FT & FL110, then why can't the VFR standard apply also?

Rather than the unneccessarily restrictive "transition layer" concept FL110 should be the "transition level".

[NAMPS]

I'm not sure this is correct, but my understanding of the existence of the transistion layer (where cruising is not permitted) is to provide a sufficient buffer between the aircraft whose altitude is derived from QNE and those on QNH.

Obviously, if the QNH is 1013.2 (ie = to QNE) then there is no need to provide for a transistion layer. But where the QNH is lower than 1013.2, there can be problems with separation.

[Capt Fathom]

Most of Asia blocks off 11000' to FL130, so our 10000' to FL110 doesn't look that bad after all.

[AirNoServicesAustralia]

Here in the UAE it's 13,000ft Transition Altitude, up to FL150 transition level. It means that we don't worry about the whole if the QNH is below this, this level becomes unavailable. A bit more restrictive I guess, but much more simple. Not that it bothers us much out here since 95% of our traffic is big jets.

[OzExpat]

In PNG, transition is 20,000 feet and FL210. In general, QNH in coastal regions is around 1010 mb while, in the Highlands, its closer to about 1017 mb.

My limited knowledge of the UK suggests that transition occurs at much lower levels and can vary at different airports. Haven't quite figured out the rationale for that yet...

[Transition Layer]

I know most of the s*hit I post on here is rubbish, but that's not very nice!

[grrowler]

shhhh, you've been told. Just go quietly, it's much more dignified... :E

[PPRuNe Radar]

Obviously, if the QNH is 1013.2 (ie = to QNE)

QNE isn't 1013.2 though. It is a variable value. For example, with the pressure at my location today of 993MB, then the QNE would be around -540 (Airfield elevation is 60').

[Spodman]

Suggested AIP AMD

2.1 Transition Altitude
2.1.1 For all operations below 11,000FT, (the Transition Altitude), the altimeter reference setting will be:
a. the current Local QNH of a station along the route within 100NM of the aircraft; or
b. the current Area Forecast QNH if the current Local QNH is not known.
2.1.2 For cruising at or above 11,000FT the altimeter reference must be 1013.2HPA.
2.1.3 QNH is available from a reporting station, the ATIS, the Terminal
Area Forecast, the Area Forecast, AERIS, or from ATS.

& ditch the silly diagram.

Much shorter anyhow.

Good bit of trivia PPROON RADAR, QNE does not equal 1013.2, and I didn't know that until I decoded your post.

QNE = What indication will my altimeter give on landing at ... (place) at ... hours, my sub-scale being set to 1013.2 millibars (29.92 inches)?

[gaunty]

Apart from separating aircraft operating altitudes and flight levels, there is a geomorphological :p component ( = they have big mountains we dont) that sets the alt/level.

The US like Europe and the Subcontintent have some seriously big lumps to traverse and the levels are set relative to those.

There is a different weather issue in the UK and europe as well but I can't recall the reasoning.

I think the US is at 18,000 because that the most appropriate level for the VFR route passes through Rockies???
In Oz 10,000 will get you you "safely" over any lump anywhere.

I don't believe it is arbitrary in any way.

[Icarus2001]

...and what is the maximum altitude in the USA without pressurisation or supplemental oxygen?

[I Fly]

Spodman and the rest of the so called experts must be reading a different AIP and have a different understanding of what actually happens. Or am I misunderstanding something?
If one aircraft flies at FL 110 on 1013.2hPa and another at 10 000' on a QNH of 980hPa, they could have a noise abatement problem. They could make a big a bang. Because they would be flying at the same Altitude / Flight Level. Admittedly a QNH below 1000hPa does not happen very often but I would not want to change Altimetry in bad weather. If it's not broken, don't fix it.

[gaunty]

Icarus2001

Same as here, nothing to do with geowhatever but just plain old fashioned breathin :)

FAR121.327 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=551b9bde5f1ca5af55531289bf3b5dc2&rgn=div8&view=text&node=14:2.0.1.4.19.11.10.21&idno=14)

FAR121.329 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=551b9bde5f1ca5af55531289bf3b5dc2&rgn=div8&view=text&node=14:2.0.1.4.19.11.10.22&idno=14)

generally have a look at here
FAR 90, 125 and 135 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?sid=551b9bde5f1ca5af55531289bf3b5dc2&c=ecfr&tpl=/ecfrbrowse/Title14/14cfrv2_02.tpl)

[Hempy]

If one aircraft flies at FL 110 on 1013.2hPa and another at 10 000' on a QNH of 980hPa, they could have a noise abatement problem. They could make a big a bang. Because they would be flying at the same Altitude / Flight Level. Admittedly a QNH below 1000hPa does not happen very often but I would not want to change Altimetry in bad weather. If it's not broken, don't fix it.

If the QNH was 980hPa, there wouldn't be anyone at FL110 because they wouldn't have a clearance at that level

AIP ENR 2.4.1

"To retain a minimum buffer of 1,000FT above the transition altitude, FL 110 must not be used for cruising when the Area QNH is less than 1013.2HPA."

The only time it becomes a problem is with adjacent FIR's with different Transition Altitudes (e.g 10000ft and 15000ft), and even then its only if two aircraft cross the FIA boundary (i.e changing from QNE to QNH and vice versa) at the same time in the same place.

[AirNoServicesAustralia]

Hempy the example given,, was in response to Spodmans idea of removing the whole section on if QNH below this, this level not available etc.

Problem with adjacent FIR's isn't just when aircraft are at the boundary at the same time. Cos in our case over in the sand pit, the aircraft we are dealing with in this area are invariably YAK's, Tupolev's and Illuyshins, so the pilots have enough trouble being on the correct frequency let alone on the correct QNH/QNE.

And just for I fly who said only an issue when below 1,000 Hpa, but hardly ever below that here. We have been 992 to 999 Hpa over here for about 4 months straight now. You soon give up on saying "niner niner niner", I can tell you. At least here there is none of that silly "trip" business so triple 9 is accepted, unless talking to an aussie pilot and then they get all worried!

[Spodman]

ARGHHH! You wound me IFLY, but let me elucidate. My amendment was for ENR 1.7 2.1. As Hempy and others have pointed out this bit doesn't talk about what flight levels you can't use. There's Hempy's bit and the table at ENR 1.7 5 that explain that. It would make sense if it was all in one spot, but that is not the AIP way...

The levels you can't fly at with low QNH would still not be there. And when they have been applied there will still be at least 1,000FT between 10,000FT and the lowest available flight level, and 500FT between 10,500FT and the lowest available flight level.

When you are climbing you know what the lowest available flight level is because you have the QNH (or it's applicable stand-ins), so you change your altimeter setting at 11,000FT. On the way down you know what the lowest available flight level is because you have the QNH so you change your altimeter setting when you pass it. POP.

There is no point or reason that I can see for locking up 10,500FT as a level nobody can fly at.