Great circle? Yes.
Earth's rotation? Yes also, oddly enough, though indirectly. The earth's rotation is, I believe, responsible for the jetstreams, the winds that blow at the levels at which aircraft fly. These move along quite rapidly in a relatively thin band, from west to east. Consequently, an aircraft flying from New York to London wants to be in them as they will increase the groundspeed and thus reduce flight time. Conversely, an aircraft going the other way will want to avoid them. That is why transatlantic flights take longer westbound than they do eastbound.
The position of the jetstream alters from day to day so the airlines will request routings based on the forecast winds (and, of course, the great circle routing). Some days a London-New York flight will fly out over Lands End, others it will pass over the Hebrides. On the night of the Lockerbie disaster, the jetstreams must have been to the south so the Clipper headed north to avoid them. It was, I believe, due to enter oceanic airspace at 57N10W which is quite far north for a London-New York flight, though not exceptional.