A few of the regional HEMS aircraft have a variety of fixed cameras mounted within (Yorks Air Ambulance, for example, to allow cabin shots for Helicopter Heroes). Four nominally I think, two mounted at the front looking back at the pilot and front passenger and then another two just in the centre behind two front seats, one giving a pilot's eye view and the other facing into the rear.
If you were that interested you could contact the BBC team that work with the YAA and ask for the spec, I'm sure they will be glad to help. They're only very small cameras from memory, but full HD etc.