[QUOTE=The Lev]I agree that AC would have a hard time filling a -300 on most routes, but presumably they could have bought -200ER's for a lower unit cost than the LR's (although I guess they'd lose out on commonality of engine parts).

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Yah I agree but AC has a lot of Long Haul flights planned HKG DEL SYD will need at least 6 777LR maybe 7? so maybe its for the "common" engine?
However AC is going to have some 333 around that are ALONE in the fleet??? so I would imagine they might be looking for more... or they are going to be traded at some point for 787's