Temperature Inversions

[Knightsky]

Would be most appreciative if those with knowledge in this area could comment on the following;

1. When operating to parts of the world where temperature inversions pose a take-off performance problem where do you ascertain the inversion values? Are they available from local ATC/MET service?

2. Are there global locations, other than the middle east, where airlines take account of temperature inversions?

3. Do those of you operating out of the middle east account for the inversion value to reduce purely the climb limit weight or both the climb limit weight and the obstacle limit weight?

4.Do operators mandate lower MAAs under inversion conditions specifically to mitigate against performance limitations?

5. Do operators use a threshold value for the inversion temperature below which its' affects are not considered? IATA seems to quote 10 degrees Celsius but do more conservative inversions get considered?

Any other general comments as to your operating practices with regard to temperature inversions greatly appreciated.

Thanks,

Knightsky

[lion-g]

Hi,

First of all, when T/O performance is concerned, we only consider surface temperature. To the best of my knowledge, there is no legislation on performance penalty whenever there an inverson layer and it's not explicitly identified by our briefing package.

However, I do brief for it when conditions suggest an inversion layer is in the region, namely high QNH, a distinct layer of smog/ chimmney smoke flattening out. Should there be a loss of power/speed, I will have go on MAX power and watch out for cleaning up the A/C while on a turn as well.

Cheers,
lion-g

[rudderrudderrat]

Hi knightsky,

From memory a long time ago - Provided Flex (assumed temperature) was 10 degs or more above ambient, then it wasn't considered a problem. If Flex was less than +10 degs, and we had a known EPR shortfall due TGT limit, then there was a performance weight penalty.

[mutt]

Have you ever seen a fully loaded B747C with a 100fpm rate of DESCENT after takeoff?? Since then we are probably one of the more conservative operators in relation to temperature inversions....

1: We involved the local MET people who provide forecasts, flight crews report actuals.

2: We only do it in the ME.

3: In our case there are no obstacles so we only account for CLIMB/FIELD.... BUT if there were obstacles we would account for them too.

4: MAA??? If its Minimum Acceleration Altitude, then the answer is no.

5: No lower or upper limit, if it is reported then its accounted for.

The highest that i have seen recorded was 18 degrees C.

Mutt