A couple of people have said that if you turn off IS (image stabilisation), then your flight photos will improve. The rationale - I think - for this, is that IS takes a fraction of a second to kick in, and thus the camera focuses slower. Actually I have no idea, but I had a go today at some Gulls on a Suffolk beach, and in doing so walked away with some keepers, which doesn't usually happen! Perhaps it was because I using a smaller lens which was easier to handle - it was always said that the best flight lens was the old 400 f5.6 telephoto, a lens which has no IS funnily enough....  I used something similar, which was the Canon 300 f2.8 with the 1.4x converter - a combination which clearly focuses quickly enough for gulls. I reckon that with practice I could get quite good, and there are plenty of Gulls here in Wanstead to have a go at.