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PETIGRAM
1st May 2003, 08:40
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

mutt
1st May 2003, 14:35
For our normal computer flight plans we base the 5% contingency on the fuel burn for the last two segments before the top of descent. At this stage the aircraft is light and therefore has the lowest fuel burn per hour. This satisfies the requirement to have the contingency fuel but may not always add up to 5% of the total trip fuel.

I guess that the same trick is used for ETOPS.

Mutt.

oxford blue
1st May 2003, 18:26
I think that we need to go back to basics here. Contingency fuel is meant to cover more than just deviations of an individual aircraft from the mean consumption of the fleet. Contingency fuel is carried in order to have sufficient fuel in the event of deviations:

a) of an individual aircraft from expected fuel consumption data

b) from the forecast meteorological conditions

c) from the planned routing or cruising levels

JAA rules (and I presume the FAA is the same or similar) for calculation of contingency fuel are one of the following, as agreed with the National Authority:

1) 5% of the planned trip fuel or 5% of the trip fuel for the remainder of the flight. No en route alternative is needed in this case.

2) Provided that an en route alternate is available this figure may be reduced to 3% of the planned trip fuel or 3% of the trip fuel needed for the remainder of the flight.

3) If the operator has established a fuel consumption monitoring programme for individual aeroplanes, keeps appropriate records and uses valid data so determined, this can be reduced to 20 minutes flying time.

4) If the operator has a fuel monitoring programme and agrees a particular method of statistical analysis which includes standard deviations, this can be reduced yet further by agreement with the Authority.

Notwithstanding whichever of (1) to (4) above is the method agreed with the authority, contingency fuel can never be less than 5 minutes.

For ETOPS, you can forget (2) above. No en-route diversion exists along the ETOPS segment. The baseline is therefore 5% unless it can be reduced by (3) or (4).

For 20 minutes flying time to be lass than 5%, the ETOPS segment would have to be more than 400 minutes, ie, nearly 7 hours. I don't think that any exist.

I presume that Boeing are therefore using (4). The full (JAA) definition is "An amount of fuel based on a statistical method approved by the Authority which ensures an appropriate statistical coverage of the deviation from the planned to the actual trip fuel. This method is used to monitor the fuel consumption on each city pair/aeroplane combination and the operator uses this data for a statistical analysis to calculate contingency fuel for that city pair/aeroplane combination".

So basically, it's the history of actual total fuel burns used over that particular route by that particular aircraft.

Hope this helps, even though I am not FAA.

PETIGRAM
2nd May 2003, 04:43
Thanks Mutt & oxford blue:

I've searched the ACs, FARs & 8400 as well as the good ol' google searches and haven't come up with anything real definitive on this process. So if anyone has information on the source documents for this, I would be appreciative of any information that you can provide - especially from someone who has actually gone through the process.

DP