Performance Factor

[ulsk]

Dear all

1. I want to know the difference of Perf Factor and Idle Factor.
2. We have an A330 aircraft with FMS1. It's idle factor is 8.5% and when we advise the Perf Factor we have advise to reduce 3% from the calculated figure from airbus PEP programme. If Perf Factor is 2.5% then we have to advise Perf Factor of (Minus) -0.5%. Can the Perf Factor be a minus figure? What is the correct method when we get the Perf Facotor for A330s with FMS1?

Appreciate your comments on these questions.

[vineet.mk]

Hi.

Perf factor changes the fuel prediction of fmc. E.g. if trip is supposed to be with 3% degradation and fmc had none. Then lets say at a point fmc says you will burn 10 tonnes to your destination. When the correct factor was set in the fmc it will would predict 10.3 tones to your destination.

Idle factor changes the idling n1 of the engine. This affects the idle descent by making it shallower for +ve idle factor. Best recommendation to check Airbus fcom.


Regarding part 2. Generally default fmc factor is 0 to represent a new factory aircraft which should burn fuel by the book. For reasons unknown to me some Airbus aircrafts have +ve / -ve default factor (this is documented in fcom). So the new factory aircraft has a +ve / -ve default factor to match the book value. All fuel factor corrections are to be made against this default value. E.g if default factor is 2, fuel burn factor identified to be +1, then fmc requires 2+1=3 as the perf factor.

Fmc implies fmgc.

[ulsk]

Thanks a lot for the info.

I want to know whether is there any different in Perf Factor for FMS1 and FMS 2 aircraft. As I said we reduce 3% only this aircraft that has FMS1. And what is the FCOM or AFM reference we can check the min and max perf factor of an aircraft. Also, FMS1 and 2 criteria regarding this 3% story.
Regards/ulsk

[vineet.mk]

That should depend on aircraft / engine / FMS type. generally its given in FCOM systems section "Auto Flight - Flight management" under heading "perf factor".

Other than that there is not reason why 2 tails of same configuration have different base factors.

[ulsk]

Thanks.

I have another question. On FCOM ref DCS-22-20-40-30 P17 onwords there are values for types of aircraft. There, should we add the calculated Perf factor to the given figure? Eg: as per FCOM A340-212 CFM56-5C3 value is -2.5%. so if we get the calculated Perf Factor as 2.9%. Should we consider the corrected perf factor as 2.5+2.9=5.4%?