In addition to using stock footage of a B-17, an Avro Lancaster, and a FW-200 Condor to all represent the same plane, the engine startup sequence is that of a B-29 engine.
The prisoner's plan to steal General Biedenbender's Heinkel bomber and use it to bomb a heavily defended refinery. Stock footage was used to represent the bomber. At no time was an actual Heinkel bomber shown in the footage. Various shots show a U.S. built B-17, a British built Lancaster, and a German built Fw-200.
Hogan goes to an airfield to steal a German bomber to first bomb a German refinery and then to transfer control of the bomber to the two, on-board American lieutenants to fly to England. Various clips of "stock footage" are used in this scene. First, when Hogan starts the engines, the engines are not part of a German bomber; they are from an American B-29. Next, it is a British bomber that taxis and starts to take off. Another clip (head-on) of the takeoff shows an apparent American B-17 Flying Fortress. Once airborne, there is a clip of a marked, German bomber. Once the bombs are dropped, there is another clip of a B-17, turning away from the target. Yet, its wheels are down.
BTW, in another piece of "stock footage," when one of the bombs hits the ground, it is a napalm bomb. And, the viewer sees what appears to be a fighter (not a bomber) in the upper-left corner moving from the viewer's left to right.
In addition to all of the other aircraft types mentioned in this category, Sgt Carter is seen sitting in the bombardier's position of a B-25 Mitchell.
When Hogan is piloting the bomber, as he moves his wheel, the co-pilot's wheel does not exactly match the movements Hogan is making.
Col Hogan is surprised when Gen Biedenbender knows Hogan's birthday. That would be no surprise as a POW is required to give his name, rank, service number and DOB (Date of Birth) upon capture.
Update: In the context of the General's revelation of his knowledge of Hogan's background, Hogan's reaction to the General knowing Hogan's birth date is more one of a little surprise combined with a great deal of concern, and curiosity about where the General is going with his revelations. If any German General came to camp and knew Hogan's birth date, it would be a matter of some concern, since, even though he would have given his birth date when he was captured, it is not something that would be generally known unless the General had a specific interest in knowing it. In this case, the General DID have a specific interest in knowing it.
After the others jump out of the plane Hogan stands in the doorway talking to the general for 20 seconds before jumping. This would put his landing miles away from the others.
Nothing is mentioned about what happened to the 4 Heinkel flight crew members. The last they were mentioned was that they were not called by Schultz before the plane took off.
Colonel Klink addresses his secretary as Helga (his secretary from the first season) instead of Hilda.
When the bomber approaches the target, Hogan tells Sgt. Carter, acting as the bombardier, when to drop the bombs. It would be impossible for the pilot to do this, which is why the bomb sight is put right in front of the bombardier.
James Gregory, as General Biedenbender, does not speak in any type of German accent.