MAMEHistory says plane formation comes from flying east - though on other levels, I think it can be west or something - though History also says the formation flies east, and I've had them come every cardinal direction.
Don't know as I've seen the bi-plane, but I haven't looked for it. I don't even have the 5k spots down; I assumed they were random.
And.....I almost beat ya spoot! I think I only had one 5k, first screen; and couldn't find water till at least level five or six; but I did get a chance at a second and I think third squadron. Got the first two, had to dodge at the last and missed the last plane of the third. AH. In any case, as I was wondering about this, I think it's easier on my vert cab. Everything's bigger.