I understand your thinking, eyeinthesky, and I agree with you.

However, I do have a little problem with mcdhu's experience of being asked to level off at 7000', when the TA is 6000'. I would also have queried it, if it had happened to me.

If the QNH had been less than 1013, then I think mcdhu should have been asked to stop descent at FL75, or even FL80, rather than at an altitude which was above the TA. Although I understand the logic perfectly about the need to provide separation above traffic at 6000', it's just that I think it is a rather "non-standard" way of achieving it.


JD
:)

Altimetry down under
 

Here in Australia: (from our AIP)

2.1.1 The system of altimetry used in Australia makes use of a transition layer between the Transition Altitude which is always 10,000FT and the Transition Level of FL110 to FL125 depending on QNH to separate aircraft using QNH from those using 1013.2HPA as a datum.

FL125 − NOT AVAILABLE WHEN AREA QNH IS BELOW 963 HPA
FL120 − NOT AVAILABLE WHEN AREA QNH IS BELOW 980 HPA
FL115 − NOT AVAILABLE WHEN AREA QNH IS BELOW 997 HPA
FL110 − NOT AVAILABLE WHEN AREA QNH IS BELOW 1013 HPA

Highest mountain - Mt Kosiusko - 7310ft.

JD

It may have been non standard - but as long as it was safe - flexibility is a tool that is often to little used - and sometimes something 'non standard' like this is used because it makes the ATCOs job easier.

McDhu had every right to question it - it was unusual and it's always worth checking - but 'unsusual' does not mean 'wrong'. ATCOs seperate aircraft, they have a fair bit of latitude in the means they use to achieve seperation.

Think yourself lucky that QFE is not also used in the TMA!!!

It was when I started flying ...


JD
:)

From ICAO 4444 CH 4.10

Note 1.— Unless otherwise prescribed by the State concerned, the lowest usable flight level is that flight level which corresponds to, or is immediately above, the established minimum flight altitude.

So regardless of separation with aeroplanes, avoiding the ground is the reason for the lowest usable flight level/transition level. No, they have a far less complicated system there, and have dispensed with most of the silly titles for things. AIM 7-2-2 says use QNH below 18,000 and set standard when climbing through 18,000. Set QNH when descending through the lowest usable flight level, (which they don't define, just list). http://www.faa.gov/airports_airtraff...7/aim0702.html It blathers on later about how to fudge a lowest usable flight level when the minimum altitude is above 18,000ft. VFR can fly at 17,500FT there, so get it right!

Spodman, I sit corrected and agree that you are indeed a true spod. It's nice to be in a place where the pressure seldom varies enough to worry - TA of 13,000 and TL of FL145, with FL150 pretty much always useable. Works for me!

Thanks for all the inputs folks - I only raised it and queried it with the Atco because it was unusual. It is entirely fair that, with someone at 6000' on a Sfd Sid, an inbound should be stopped at 7000' Qnh notwithstanding the TAlt.

Thanks to all the TC and Lgw Atcos for the fantastic service over the years.

Cheers
mcdhu