The open cockpit in the rain caught my eye too, as did the kind of stock relationships, such as the ground crew, the father and lover. I'm not from those times so I don't know how much these things ring true. Presumably those that adapted it for the screen decided that's how it had to be to make a complete film and I assume Wellum had some say in it.
You have to remember that this film was not made for experts but your typical, perhaps slightly discerning, viewer. Corners have to be cut, love stories introduced and so on. Having Wellum narrate was a clever device that added to my thoughts about the whole theme - this old man, look what he did when he was young.
I've read the book so I didn't learn anything from this film, but on the whole it worked well for me. The ninety minutes wizzed by.