That's mostly to do with the premium heavy cabin config. Apparently there's lower demand for F/J on the LHR flights than the LAX flights. But with the A380 they've gotten rid of that distinction. Go figure.
wn700driver From , joined Dec 1969, posts, RR: Reply 9, posted (1 year 8 months 2 weeks 6 days 17 hours ago) and read 3881 times:
Quoting rmm (Reply 8):
The GE has a better fuel burn than the Roller with or without the extra tank. The GE is also somewhat lighter as well.
That. And it may also be that GE has an exclusive (had I guess since you can't buy a new 744ER anymore) on that subtype the way they do on the 77W & 77L/F. Otherwise, fuel burn aside, QF may very well have stuck with RR, being that there are only 6 ERs in the fleet (and world for that matter). It can't be a very good economy of scale, I would think...