Both aircraft flown in the movie, JA-3 and JA-4, are supposed to be jet aircraft (hence the JA identifier). However, neither aircraft has air intakes that are necessary for jet engines to operate.
When Troxell first taxis the JA-4 it can be seen that the 4 on the side of the plane was just a decal placed over the 3 on fuselage used for all the ground scenes.