Airbus FOVE
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Joined: Sep 2005
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From: around
Airbus FOVE
Hey guys,
If there are any Airbus pilots with experience in the "FOVE" performance calculation, some of you might probably be able to answer the following question:
Is the 3% performance gain per 10 degrees difference between actual OAT and Flex Temp. (TAS Effect) already considered in the calculation results (ASD, TOD), or does it actually work like a regular program and you have additionally this hidden margin???
I have heared many different opinions and couldn't find any detailed information about that...
Thanks guys
If there are any Airbus pilots with experience in the "FOVE" performance calculation, some of you might probably be able to answer the following question:
Is the 3% performance gain per 10 degrees difference between actual OAT and Flex Temp. (TAS Effect) already considered in the calculation results (ASD, TOD), or does it actually work like a regular program and you have additionally this hidden margin???
I have heared many different opinions and couldn't find any detailed information about that...
Thanks guys
Last edited by NYC; 14th August 2007 at 00:34.
Joined: Jan 2005
Posts: 1,266
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From: uk
I take it the margin you refer to is that resulting from GS being lower and thrust being higher at the actual OAT when using a flex takeoff temp.
If so, the margin is 'extra'. The figures should come out (almost) the same if you put your flex temp back in as your OAT and look at the TOGA figures. I say 'almost' since it is an iterative process and small differences/discrepancies can creep in.
Ultimately you do have a bit of performance margin on the safe side, abive the FOVE figures.
If so, the margin is 'extra'. The figures should come out (almost) the same if you put your flex temp back in as your OAT and look at the TOGA figures. I say 'almost' since it is an iterative process and small differences/discrepancies can creep in.
Ultimately you do have a bit of performance margin on the safe side, abive the FOVE figures.
Only half a speed-brake
Joined: Apr 2003
Posts: 4,459
Likes: 136
From: Commuting not home
The TAS difference margin is yours to keep.
Using this TAS calculator with 1013 hPa 20°C and 130 IAS, TAS comes at 134 kt.
For assumed OAT of 65°, TAS is 144 and FOVE calculates all performance based on G/S 144 (assuming 0 wind).
However, at 20° OAT you will achieve IAS 130 ten knots earlier during takeoff roll than calculated (runway length margin).
For a V1 cut, you also have the energy margin. Performance calculation covers 1/2*60000kg*72mps*72mps = 155,5 MJ to be stopped (TAS 144 kt = 72 mps), but your V1 of 130 kt in fact (OAT 20) represents only 134 kt TAS hence the energy to lose is only 134,7 MJ. That is only 86 per cent of what had been accounted for.
FD.
Using this TAS calculator with 1013 hPa 20°C and 130 IAS, TAS comes at 134 kt.
For assumed OAT of 65°, TAS is 144 and FOVE calculates all performance based on G/S 144 (assuming 0 wind).
However, at 20° OAT you will achieve IAS 130 ten knots earlier during takeoff roll than calculated (runway length margin).
For a V1 cut, you also have the energy margin. Performance calculation covers 1/2*60000kg*72mps*72mps = 155,5 MJ to be stopped (TAS 144 kt = 72 mps), but your V1 of 130 kt in fact (OAT 20) represents only 134 kt TAS hence the energy to lose is only 134,7 MJ. That is only 86 per cent of what had been accounted for.
FD.
Thread Starter
Joined: Sep 2005
Posts: 28
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From: around
Many thanks for this excellent explanation...especially the "stop case" is not discussed in any book!!
So this means FOVE does not take into account this margin and we always have it @ a "Flex T/O"??
greetings
So this means FOVE does not take into account this margin and we always have it @ a "Flex T/O"??
greetings
Only half a speed-brake
Joined: Apr 2003
Posts: 4,459
Likes: 136
From: Commuting not home
So I was told. And I think it is not PERF program specific. You are required to calculate PERF for assumed temperature of xx deg, and there are lots of little differences such as this.
