Hey,
Got the same problem. Looking on another forum I found a hint : some Sabre guys die without warning, and the mission fails without a message...
When the plane starts its engines, it starts turning on the left. It's got some sort of gun ( ? ) on its front that might hit sabre guys and kill'em...
Poorly designed mission.
What I did is : save before getting into the plane, and restart until no sabre guy was killed :eek:
Ugly, but works without cheating.