How to determine Transition Level
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How to determine Transition Level
Lets say Transition Altitude for an aerodrome is 5000 ft, the QNH is 943 mb. What will be the Transition Level (assuming the max depth of the transition layer is 500 ft)
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17*28=476
1013+17=1030 i.e. 1031 down one level (50 to 40 )
1013- 17=996 i.e. 995 up one level (50 to 60 )
995-36= 959 one more TL 70
...
so it could be TL 70.
But other question remains. QNH 943?? Where are you working when you meet such low pressure?
We had in past some military code for met data. Only two digits represents QNH. If number is below 60 than it should read 1054 eg, if it is higher than it is 972...
so 943, is out of our military reach, obviously.
1013+17=1030 i.e. 1031 down one level (50 to 40 )
1013- 17=996 i.e. 995 up one level (50 to 60 )
995-36= 959 one more TL 70
...
so it could be TL 70.
But other question remains. QNH 943?? Where are you working when you meet such low pressure?
We had in past some military code for met data. Only two digits represents QNH. If number is below 60 than it should read 1054 eg, if it is higher than it is 972...
so 943, is out of our military reach, obviously.
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Amended as I have found in the UK MATS Part 1 a table which gives a definitive answer which says the transition flight level will be FL70.
Google UK MATS Part 1 (CAP493) and open up the Adobe download, search for Appendix A (page 479) and there is a table showing this, can't find out how to shrink the link so will post if I find out!!
Link to the pdf download here, just open the document and type in page 479 at the top.
Google UK MATS Part 1 (CAP493) and open up the Adobe download, search for Appendix A (page 479) and there is a table showing this, can't find out how to shrink the link so will post if I find out!!
Link to the pdf download here, just open the document and type in page 479 at the top.
Last edited by Wham Bam; 12th Mar 2015 at 10:15. Reason: Found answer and link
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If I'm not wrong, the simple formula should be;
TL=transition level
TA=transition altitude
TL=TA+(1013-QNH)*28
In your case:
TL=5000+(1013-943)*28
TL=5000+(70)*28
TL=5000+1960
TL=6960 --> rounded to a ('000) FL means FL70
TL=transition level
TA=transition altitude
TL=TA+(1013-QNH)*28
In your case:
TL=5000+(1013-943)*28
TL=5000+(70)*28
TL=5000+1960
TL=6960 --> rounded to a ('000) FL means FL70
Except that ICAO is in the process of changing TL so that you will always have at least 1000 ft between TA and TL in order to permit cruising at both levels with separation. As someone said earlier, it's effectively going to formalise MIN STACK. Should be coming to a MATS 1 near you soon I'd imagine.
