I'm guessing the air marshal means "what the hell were you thinking"; Holden is agreeing, indicating that he has learned his lesson and acknowledges the error; and the air marshal is then graciously moving on.

It was a ballsy move, done with the best of intentions, could have been fine, but near-catastrophically wasn't. Lesson was obviously learned, and both the shortcomings in judgement and in the regs were addressed. I'm glad they let the guy go back to work. It's not like he exhibited a pattern of recklessness. I feel like these days, it's less likely a person of authority would exercise the kind of discretion that leads to a sensible outcome. Not because they don't want to, but because liability and PR have become such institutional boogeymen. ('Course maybe I'm wrong!)

Edit: fergal_reid’s reply below is correct. Porter did serve several years at the start of his career as a pilot, in the early 1930s, before spending the bulk of it as a signals officer. Holden also had his wings, but never served as a pilot. I read Porter’s comment as a joke between two RAF officers who were not “really” pilots, but now I’m not sure how to read it.

0. https://en.wikipedia.org/wiki/Kenneth_Porter_(RAF_officer)