Performance - TAS-Effect and Safetymargin Flatrated engine

[Engine3firehandle]

Hi,
I got the following question and I am still a little puzzled :rolleyes:
If you got a flatrated engine ( as most engines are nowadays ) and you are doing T/O calculations, your data will give you most probably a flex Temp and a V1 Vr and a V2 speed.
now there are two formulas:
1. Per each 10 degrees difference between OAT and Flex you got 3% more stopping distance then calculated out of the TAS ( True Airspeed Speed ) Effect.
( A high Flex Temp at 40 degrees and an OAT of actual 10 degrees brings an 9% margin on the Accelerate Stop distance or was it the TOD ?
That was the first question.
2. The other rule of thumb is: Per 1 degrees celsius Delta between Flex Temp and OAT, you got another 10m more stopping distance.
What if you got a high elevation (3000ft, engine is flatrated 32 degrees and the Flex Temp is 60 and the OAT at 3000ft is 9 degrees C )
That would mean another 510 meters stopping distance. Is this correct ?
From 60 to 29 is the Flex Range. ( At higher GW the Full T/O thrust has to be used )
Might it be only the 31 degrees times 10 meters ?
Please help...
:rolleyes: :rolleyes: :rolleyes:
Thanks a lot.

[Engine3firehandle]

So is this correct ?

you FLEX on T/O and got an OAT of 10Celsius and your calculated FLEX is 60.

Now the stop margin shows 2 meters only.

But you got a margin actually from about 500meters due to the TAS effect.
So you brief for RTO we got a stop margin of 502 meters.
This is common practice in my company and I am not sure if this is o.k.

Any ideas ?
Guess no performance gurus here ?

[CR2]

Try asking this in TechLog... that's where the experts usually hang out.

[Mad (Flt) Scientist]

As suggested, Tech Log may be a better bet. This is right up Old Smokey's street.

or check out a few of these threads (http://www.pprune.org/forums/search.php?searchid=1572476)

As you can see, derated takeoff performance is a popular topic....