B777 PACK MEL & Weight Penalty
 

Hello all,
This is a regarding B777 300ER/200LR

Doubt -

MEL (21-51-01)
on PACK L OR R (I understand every operator will have slightly different MEL based on their a/c specifications)

One step in the (O) ops PROC mentions -
REDUCE PERF LIMITED WEIGHTS

for TAKEOFF/LDG 300ER(GE90-115B) - 5262 Kgs
ENROUTE - no penalty

for TAKEOFF/LDG 200LR(GE90-100series) - 6713 Kgs
ENROUTE - no penalty

Q1) assuming PACK EXTRACTS AIR from the ENG, one pack now under MEL, and 'lesser' load on the ENGINE, why is there a higher weight penalty (at all) for TAKEOFF/LDG ? (Emphasize PERF LIMITED WEIGHTS & not structural or Landing weight restricted).

Q2) What is the reason behind the 200 LR Having a weight penalty of 1.6 T more than 300ER. (I know it's a diff engine)

Apologies if I have missed anything too obvious.

Thanx
Regards.

Now we are two doing the same exercise in the SIM, went through all the books and couldn't find an explanation, except a wild guess.... the EEC'S compute the thrust limits based between other things on pack configuration, well here we have an EEC calculating for a pack off limit thrust and the other one for a pack on conventional take off, therefore asymmetric thrust limit on a performance limited take off, am I anywhere close to the answer? hope someone can clarify with more substance...

Q1. When one pack is inoperative, the other pack runs at a higher flow to compensate - this creates a higher demand for bleed hair from one of the engines.

RTOW calculations assume an engine failure at V1 - continue - and meet the minimum climb requirements. In the example above, the most critical engine failure would be the failure of the engine with the pack inop (for example - L. Pack inop, Left engine failure is most critical). Now the remaining engine needs to provide enough thrust to meet the minimum climb gradient, AND provide higher than normal bleed supply for the operating pack.

This is why there is a weight penalty. (Although I agree, intuitively, a failed pack should translate into a lower bleed demand and more thrust being available). You have to remember that the RTOW is for the more critical engine failure.

GOOD ONE!!I somehow suspected that it had to do with an asymmetry generated by different demands from the packs at performance limited weights, never thought in terms of the most critical engine though....
Thanks for that

@Flapsupdown - thanx for ur reply. Verified your Input with the Amm Info, makes perfect sense. THANKYOU :)

Actually, I could use a bit more explanation. In terms of normal pack operation, what happens when an engine fails. Is the pack on the failed side inoperative?

And in the above scenario, what is the difference in pack operation when the critical engine has failed versus the non-MEL aircraft.