I have to characterize this as a bug. A formation flight of bombers on two occasions (different types of bombers in each instance), were attacked. After the lead bomber was destroyed and possibly engine killed on its plunge to the sea / ground, the engine on all bombers died. I can't tell if they would have restarted on their own or not. This is mainly because it was a high speed chase and I quickly toggled the engines to get the propellers churning again.