B777 LMC question
 

I've been operating 77L and 77W (777-200LR and 777-300ER) for more than two years now and always been curious about LMC limits at hight gross weights. Our OM states, that at TOW more than 340 000kg (77L) and 345 000kg (77W) any LMC exceeding 100 (one hundred) kg would grant a new loadsheet.
I've always thought this number is a bit extreme - shurely, a big and heavy aircraft like this could not be very much affected by such a small change!
Any thoughts and additional info would be greatly appreciated!
Cheers!
H.L.

Hi Homo Ludens,

Are you close to Max Authorised Mass?

It could be to ensure that you don't inadvertently exceed Max Taxi or Max T.O. mass.

No, I don't think that's the case. We are talking good 6 to 7 tons to the MTOW. We were told it's for the ballance, not the weight.
Anything else?

Hi,

Then there must be a very narrow %MAC allowed as you approach Max Authorised TO. Wt. Do you have a manual load sheet to look at?

Edit: On L1011 - 50, we obtained a greater Take Off weight by restricting the Zero Fuel Weight, and not allowing the C of G to go too far forward, thus reducing the down elevator force and hence the total bending load on the wing.

In general, as you reach very high gross weights the narrower the cg envelope becomes, sometimes you`ll need fuel in trim tank to be able to achieve mtow , aircraft type and load dependant of course....
Having said that a 100kg lmc tolerance sounds a bit daft when you consider that the passenger weights are only standard weights thus being wildly inaccurate in the first place...

-jd

The 777 has a rather wide balance envelope which doesn't particularly narrow at the top, except if you're at the extreme ends. It's actually at its narrowest at the bottom.

B777F Balance Envelope (Boeing sample Loadsheet):

http://i43.tinypic.com/2ebzk9d.jpg

Compared to this one, it's a doodle

MD-11F Balance Envelope (LCAG)

http://i44.tinypic.com/2m5xqgm.jpg