ETOPS 5 percent penalty in fuel mileage
Many newer A/C, during ETOPS Ops, are using actual data on fuel performance deterioration, for each specific A/C, in lieu of the "5 percent penalty in fuel mileage", as specified in AC 120 42A. Is there a more expansive and recent document that further defines the "5 percent penalty in fuel mileage?" AC 120 42A does not elaborate on it.
Computer Flight Plans show figures which are in the neighborhood of 3% of total fuel burn so there is clearly more (or less) to the 5% penalty than an additional 5%. I cannot locate a precise definition of how this is computed.
Do Boeing A/C use the FDAMS program to extract the data necessary to support requesting actual fuel performance figures in lieu of the "5 percent penalty in fuel mileage." Is it necessary to extract Fuel Flows at intervals, or will the FAA require comparisons of projected overall burns to actual? How long do you need to collect the data to verify it?
It's fine with me if this discussion breaks out into which country or regulation system does this better or worse, but in the beginning I would prefer to limit responses to just US carriers - at least until I get my answers.
If anyone has specific experience with this program, I would appreciate any information that you can provide.
Thanks,
DP