All true, but again, you have to factor in the cost of maint. and AOG's.

By the way, I'm having a little trouble following the math on the spark plug
equation. An R-4360 has 28 cylinders x 2 plugs per cyl. = 56, not 72. So a
B-36 would need 336 plugs @ $5 = $1680. Not terrible considering what turbine
blades on a JT-8D probably cost. But here's the rub: how long does it take to
change a spark plug in a tightly cowled and baffled radial? Lets see, at a
bare min, you'll have to pull the wire, the "cigarette", and the old plug, gap
the new plug, and then put it all back together. That's IF you don't have to
pull any baffles or pannels to get at it... which you probably will.

I know a few old KC-97 pilots who told me they would be AOG for days while the
plugs were changed.

Harry "engine? what's an engine?" Frey