Airbus performance factor MINUS

[Longjon]

What is a minus performance factor mean would appreciate any views

[Fursty Ferret]

It just means that it's slightly more efficient than the generic model that the performance model is based around.

[nitpicker330]

- good :ok:
+ not so good :eek:

[mikedreamer787]

See "+" a lot and the odd "0.0" on newer 320 suck-squirts.

Never seen a "-" on any airbus.

[Longjon]

Does it mean that the engines will burn less fuel than what the flight plan depicts ? I have seen this on A330 with rather old engines a little hard to swallow

[nitpicker330]

All our new A330's in the last year have -3.0

And they do seem to burn a little less at the end of the day so I guess it's right.

[Down Three Greens]

There is a generic FMGC model for each aircraft type. i.e. A320, A330 etc. In order to tailor each engine type and airframe this is adjusted slightly. An A321-211 (CFM-56 5B3 with singular annular combustion chamber) may be 1% more efficient than the generic model. It will have a bias of -1. The dual annular combustion chamber version may have different bias. Add on top of this the degradation from engine and airframe wear/drag as the aircraft ages, you get the the FMGC bias. So, aircraft/type bias (contained in the FCOM) + increase in drag/fuel burn % = FMGC bias.

Google 'Getting to Grips with Performance Monitoring' from Airbus.

[Longjon]

Good answer thanks but still there are old airplanes with old engines and
The per factor is minus how come ?

[kumul1]

Very rare to see a '-' performance factor on a bus, if the performance blokes are constantly monitoring and updating. Not a single plane on EK's inventory with a -. There were a few A330's a few years ago but all in the + now. Even the new A380's are starting with 0.
Maybe the Perf guys just want to be conservative.

[J.L.Seagull]

@LongJon:

I used to be an engineer at EK. They had a couple of old 777s, MIKE series, where they wanted us to do a complete re-rig of ALL the flight controls.

Directive was not just to get the values within AMM tolerances, but to rig everything as perfect as was possible. And we did... and apparently they got somewhere between 1% and 2% better fuel burn than before.

Mind you... those two airframes were singled out - or doubled out :rolleyes: - for poor fuel consumption anyway.

So it is possible for an airframe to go in for a major check, and have everything re-rigged, (not just flight controls, but doors too... pax, cargo, gear) AND the airframe polished back to it's factory shine, AND the engines washed, and you could get a -ve perf factor.

LOL! Dunno why, but the term cougar-town comes to mind! he he he...

[myekppa]

Although I haven't bothered to check, EK may not currently have any aircraft with a negative performance degradation. Despite other comments here that wasn't always the case, especially on the GE powered 777's.

Most of the early 300-ER's were running degradations in the range of over -3.0% and still burning substantially (tons not hundreds) of kilos less fuel than the -3% flight planned. Let's face it, TC ordered the aircraft on the back of published performance specs so it's little wonder that he went on to order 170+.

They seem to have sorted out the true performance figures and Boeing are delivering aircraft with 0 which just means they have the data to sharpen the pencil to an accurate number.

Can't speak for the bus, but the 380 economics obviously work as well otherwise they wouldn't be clogging up the pavement.