Bus Ecam Cg and Trim Sheet Cg difference

[Seagul1]

Was wondering if its ok to go with the diff. of more than 2% between the ECAM CG and Trim sheet CG (MACTOW) if you use the Stab setting for the ECAM Cg from the QRH. Would appreciate comments alternate procedures.:confused:Thanks

[TyroPicard]

On the A320 Airbus recommend using % MAC only (from the load/trim sheet) to set the THS, to avoid any Up/Down confusion.

[pensador]

TyroPicard (http://www.pprune.org/members/15940-tyropicard) is right. the main prosedure reccomends you to use the CG from the load sheet. but! Who knows that the figures from the load sheet is right? We have to believe in that figures and in your experience. I can remember the takeoffs when the real CG differes from the load sheet. You can feel it during rotation. The forward CG gives no sufficient problems, but with the aft CG just bee careful to avoid tailstrike!
Be happy, Pensador

[Iceman49]

Agree with all of the above, and make sure its in the green.

[ALK A343]

On the A320 series you have to go by the Loadsheet C.G. and stabtrim setting as it does not indicate your actual C.G. on the ECAM.

The A330/340 have provision to indicate the C.G. location on the ECAM. It is necessary because of the trimtank and the associated fuel transfer.

So if you get two different figures on the ECAM and the Loadsheet it depends on your companies SOP, whether you can use the ECAM figure or not.
In our company if the difference is more than 2 % and the data entry into the FMGC is confirmed as correct we go by the ECAM figure and set the stabtrim accordingly.
But do not follow this procedure unless you get clarification from your company.
Regards,

[Seagul1]

Didn't know the 320 was different anyway did find a mention of the Procedure in the Airbus manuals 330/340 and they say use the ECAM Cg. Thanks Guys Cheers:ok:

[shortfuel]

By referring to Ecam CG, GWCG (generated by FCMC), Seagul1 was considering A330/340 procedure.
A320 skippers, you don't have a CG displayed on Ecam (read the question ;))

>2% difference is the value that will trigger a sorough re-check of your ZFW and ZFWCG, you rely on Ecam CG in any case (given you did a proper re-check).
In any case you set your THS according to ECAM.

On A330-200, you can accurately set your THS easily without referring to your QRH:

ex.:
If ECAM CG before pushback is 28%, first THS is always nose up:

THS is (35-GWCG)/2 = (35-28)/2 = 3.5UP easy ;)

(why? because by design, THS is a linear application of TO CG)

[Trevelyan1975]

Is it correct to say that we could rely on ECAM CG and Load Sheets are no more considered as mandatory when it comes to TSH settings. ( A330's ) :rolleyes:

[vilas]

Even on the A320 after start progress page shows GW CG and that can be set. Some airlines follow this procedure. Since its a computed value there is no reason to differ from LT. Check the load sheat and FMGS entrees.

[JABBARA]

In fact, there are reasons for the differences between Loadsheet CG and ECAM CG.

Loadsheet assumes an ideal fuel distribution for a given FOB, but real fuel distribution may not be so. For A 330, if somehow -even small- amount of fuel left at Trim Tank (e.g due to some maintenance check) and the FOB is less than 36500 Kg, then ECAM CG may be quite further aft of the LS CG.

Apart from this, real Fuel density may also effect this difference particularly when all tanks are full. This is because, LS is also prepared by assumed fuel density unless it is specifically given for that fuel loading. Even small differences between LS assumed Fuel density and real measured density by tank densimeters, may cause big difference between two CGs when the amount of FOB is near max.

The reason for 2% is another story. The LS CG limits are operational limits and these limits are, in general, around 2% shrinked (narrower) than the Certified envelope (as published in FCOM). When ECAM CG is diffrent than LS CG, practically there is no way to ensure this CG is still within Certified CG envelope, unless this difference is less than 2% :8