Only officers of the Air Force in the following categories may be rated as flying officers:

((1)) Officers who have aeronautical ratings as pilots of service types of aircraft or as aircraft observers.

((2)) Flight surgeons.

((3)) Officers undergoing flight training.

((4)) Officers who are members of combat crews, other than pilots of service types of aircraft, aircraft observers, and observers.

((5)) In time of war, officers who have aeronautical ratings as observers.