On the subject of redundancies, this one has always bemused me. ‘Heaven pilot’ or something of the kind I could understand, but in what way is someone who just flies an ordinary aeroplane not a ‘sky’ pilot, as much as or more than a padre?

I suspect, and others here certainly can and will correct or support me, that the term sky pilot predates the existence of aviators.  By the time there were aviators the term was probably common enough that it precluded its use for that sense.

The OED has sky pilot from 1883. The first citation is from George W. Peck’s Peck’s Bad Boy and His Pa, a compilation of Peck’s newspaper articles that featured his “Bad Boy” character, a mischievous lad who liked to play tricks on his father, sort of a nineteenth-century Dennis the Menace.

but in what way is someone who just flies an ordinary aeroplane not a ‘sky’ pilot

Strange and illogical are the ways of language. Even if sky pilot had been coined after the advent of aviation, there is no reason why this particular construction could not have a narrow meaning. We don’t use gunman to describe a police officer, for instance.

I have scurried hastily to the online OED (which of course I should have done before posting), and find to my amazement that it dates from the 1880s; for some reason I had always taken for granted that it was WWII slang. It doesn’t actually predate the ‘flier’ sense of pilot, which (again to my surprise) goes back to the 1830s in the context of balloon flight. But the early citations for sky pilot make clear that it was sailors’ slang, and of course in a maritime context a pilot is someone who guides the master of a vessel safely into port, not the driver of the vehicle, so to speak. So in fact it’s a perfectly apt metaphor.

1883 G. W. Peck Peck’s Bad Boy 177 Look-a-here you sky-pilot, this thing has gone far enough.
1888 W. B. Churchward ‘Blackbirding’ in S. Pacific 22 A dock missionary (we called him sky-pilot).
1893 Spectator 30 Dec. 952/2 A ‘Sky-pilot’, in sailor’s parlance, is a clergyman generally, and specially a clergyman who has a spiritual charge among seamen.

Diegogarcity. I was just looking at the lyrics to the song, Sky Pilot by Eric Burdon & The Animals. The Sky Pilot of the song is a military chaplain.

I believe pretty much all “sky pilots” are military chaplains.