D.B. Cooper exited the Boeing 727 into a 500+ mph windstream and was instantly sucked ass-over-teakettle into his parachute and fell thousands of feet to his death. Simple.
Airstair door wouldn’t open at cruise speed. Cooper told the pilot to fly 200 mph at 10K Feet so he culd make it out.
The fact that he got the chutes from the FBI tells me why he didn’t survive.