Trans Alt and First Useable level (UK)

[zerouali]

Title pretty much says it all!

How much separation should be provided between trans alt and first usable FL? Flying today in an area with a trans alt of 6000ft we were cleared to FL060. QNH was 1023 so I understand that FL060 was above 6000ft (by around 250ft) but I was always under the impression that the first useable FL had to provide at least 500ft clearance from traffic flying on QNH?

In the TMA we'd always get A6000 or FL070, just curious why this wasn't the case at this particular location?

TIA.

[fireflybob]

>but I was always under the impression that the first useable FL had to provide at least 500ft clearance from traffic flying on QNH?<

Then I believe you have been under the wrong impression!

Working from memory here but doubtless I will be corrected if wrong:

The Trans Alt is the Alt at or below which the vertical position will be expressed in terms of an alt based on QNH.

The Trans Level is the Flight Level at or above which the vertical position of the aircraft will be in terms of Flight Levels based on 1013.25 mb (=29.92 " Hg).

As far as I am aware there is no requirement to have any specificed interval between the TA and TL - indeed they may be coincident if the QNH is 1013.25 mb!

Individual units will have a minimum Flight Level (depending on the QNH) in order to have standard separation from an a/c flying at the Trans Alt.

Hope this helps!

[zerouali]

Individual units will have a minimum Flight Level (depending on the QNH) in order to have standard separation from an a/c flying at the Trans Alt.


That's the bit that's confusing me! If another aircraft was at 6000ft QNH and we were at FL060 we would be only 250ft apart, that's not separated.

[fireflybob]

You cannot assume that flying at the TL will give you any separation from the TA!

[Lookatthesky]

That's the bit that's confusing me! If another aircraft was at 6000ft QNH and we were at FL060 we would be only 250ft apart, that's not separated.


But if there are no 'other a/c' at 6000ft, then there is no problem!!

We regularly descend a/c on a shortened routeing into EGGW to FL60, we also ensure that there are no a/c at 6000ft QNH in the vicinity when we do this. :ok:

[chevvron]

ATC units should have a chart or something showing them the lowest level above TA for different QNH's, and should allocate flight levels in accordance with this. At the college, we were always taught that the Transition Layer ie the bit between TA and TL, wold always be less than 1000ft and in some cases would be 'insignificant'.

[Delta Whiskey]

No doubt different here in Godzone to up in Europe, but we have a transition layer - going up it starts at 13,000feet, passing which you set 1013 (standard setting), and it ends at F150.
The reverse applies in descent - passing F150 you set QNH, and you vacate the layer at 13,000.
Obviously none of the levels/altitudes between 13,000 and F150 are available for use.
Sounds a lot simpler than what is described above.
Cheers

[2 sheds]

ICAO recognises 4 systems (or used to - I don't have the documents immediately to hand).

A variable transition level (depending on actual pressure), with or without separation from the transition altitude, or a fixed transition level (in areas of little pressure variation), again with or without separation from the transition altitude.

The bottom line is that even if there is no separation between the TA and TL, if there ain't any conflicting traffic at the TA, it matters not a jot if the TL is allocated - it might be a useful tactic to free the level above.

[This is a crisis]

The way we work it is as follows:
Mats Part 1 gives a table to determine the Transition Level dependant on the QNH and the Transition Altitude
e.g. Transition Altitude 3000', QNH between 996 and 1013 give a Transition Level of FL35. If you then add a 1000' to that you get what we call the Lowest Available Flight Level which obviously in this case would be FL45. This would then be the lowest level we would allocate which would give standard separation between an aircraft flying at 3000'. All our stack levels then follow on from this.

Is that what you were after or have I got the wrong end of the stick?

[Mr_Nightman]

If by chance you were flying for Scotlands favourite airline and heading south towards mainland UK ,then the preceding aircraft had just passed FL60 in the climb as shown on our radar so you were cleared to FL60 to be separated from that traffic,there was no traffic in the vicinity at 6000" QNH.If there had been then the clearance would have been different.Hope this helps.

[zerouali]

Mr_Nightman - Yep, sorry for being a pain, I do trust you, honest!:O

I think I had managed to confuse my first usable level and transition level, assuming them to be the same thing. If I've now got it clear in my head, in the climb F060 is fine as it's above trans alt, but in the descent you would clear to F070 then an alt below that?

[5milesbaby]

To add another possibility in (I know you have your answer but just for future), there are a few low level airways in/out/alongside of the TMA too so if you are on the edge and about to enter the airway then a FL could be used to separate from a/c in the airway on 1013mb at say FL50.

[Mr_Nightman]

Correct,in the descent FL70 then altitude.

[anotherthing]

Transition altitude is set for your area

Transition Level is TA corrected for pressure - it could be FL63 - i.e. not a real FL....


the MIN useable FL is first real FL that gives a minimum of 500' difference between the itself and the TL i.e. in this instance FL70 (Not FL65)

The transition layer is the difference between the MIN useable FL and the TA and could therefore be in excess of 500', but should never be less than.

Hope this is useful (and factual)- a bit early in the morning for a day off, and taken from a long and distant military flying career

[issi noho]

I've asked this in another thread but never got a straight answer;

Given the definition of trans alt stated earlier on this thread why do MAN approach often issue descent to altitude 6000 ft when their trans alt is 5000 ft? Does any other NATS unit do it and is it an acceptable clearance with any references to it in MATS pt2.

Ta in advance.

[PPRuNe Radar]

Transition Level is TA corrected for pressure - it could be FL63 - i.e. not a real FL....


the MIN useable FL is first real FL that gives a minimum of 500' difference between the itself and the TL i.e. in this instance FL70 (Not FL65)

The transition layer is the difference between the MIN useable FL and the TA and could therefore be in excess of 500', but should never be less than.

anotherthing

Not quite ;) but your defence of it coming from your distant military past explains the confusion :p

In the UK, the Transition Level is the lowest Flight Level available for use above the Transition Altitude. It is determined from a table, based on the TA and the actual QNH.

So Transition Level does not equal the Transition Altitude, but actually equals what you have called the MIN useable Flight Level. Thus Transition Layer actually equals the layer between the Transition Altitude and the Transition Level :ok: . It is also important to remember that it should not be assumed that separation exists between the Transition Altitude and the Transition Level.

issi noho

Given the definition of trans alt stated earlier on this thread why do MAN approach often issue descent to altitude 6000 ft when their trans alt is 5000 ft? Does any other NATS unit do it and is it an acceptable clearance with any references to it in MATS pt2.

Quite possible, and acceptable, since the AIP and MATS Part 1 state ''Vertical positioning at, or above, any Transition Level will normally be expressed in terms of Flight Level.'' This, by default, allows altitudes to be used in situations which are not normal. The controller may want to provide 1000' separation from an aircraft climbing to 5000' for example, but knows the Transition Level does not provide this, or maybe the Minimum Stack Level available is 'wasting' a few hundred extra feet because of the QNH value and the inbound is non pressurised which limits late descent possibilities. Or perhaps a transit aircraft at FL60 needs to be 'adjusted' to 6000' to ensure separation from outbounds. Plenty individual reasons exist, and the UK ANO permits aircraft to be varied from the semi circular IFR levels for level flight if so directed by ATC.

[zerouali]

anotherthing - You almost had me going over the edge again there!:}

That was the picture I had in my head, which is why I was so confused by the clearance I was given.

All clear now though. I think........:p

[issi noho]

P Rdr

Thanks, I accept all you say. It happens as part of the approach function (I have no knowlegde of low level MAN over flights) so in effect it is a 'normal' situation (pressurised jet aircraft). I have never experienced it at any other airfield (where min stack seems totally acceptable to get a cross) and am still wondering if MAN has something written about it in pt2 or if it just an individual watch procedure.

[PPRuNe Radar]

:ok: Maybe one day Manchester TMA (and the rest of the UK outside the major TMAs) will move to a common Transition Altitude which will remove the practice, or at least standardise it. The CAA have only been considering it for at least the last 10 years so it must be a really tricky calculation for them to decide what it will be :hmm:

[yarrayarra]

Our transition level is 10,000 and first Flight Level F110. F110 is above our highest terrain so:-
When the Area QNH is below 1013 F110 is not available
below 997 F115 is not available
below 980 F120 is not available
as 1 hpa = about 30ft there is always at least 1000ft between A100 and the first available Flight Level.
Additionally there is never more than 5 hpa between any local QNH and the Area QNH thus ensuring the tolerances allowed within the 1000ft separation standard are not exceeded