Mick and The Old Fat One
Before we leave the APU issue altogether, I've consulted my notes of the coroner's words on Friday. I find that, even if some ex Nimrod crew don't seem to be able to remember how it all worked, the coroner was perfectly clear.
He said that No 3 engine was started using the APU in the tail, which provided air via 4-way ducts to the engine's air-start mechanism. The APU was then shut down, and No 4 engine started using another air connection from the No 3 engine. I and 2 were then started using air from 3 via the crossfeed duct.
airsound