[noiseman]

”...in the 727, how in the word did they keep that enormous door for the rear stair closed against cabin pressure when at high altitude?”

There was a more conventional door at the back of the cabin that maintained cabin pressure and that would have to be opened first. The air stair was in an unpressurized area of the fuselage beyond that. From what I recall, D.B. Cooper had the pilot descend to an altitude at which the cabin could be depressurized, permitting him to exit via the rear airstair.

After the D.B. Cooper incident, airlines were required to install small vanes on the exterior of the airstair that generated a vortex and made it impossible to open that door in flight as well.

[Steely Tom]

There was a more conventional door at the back of the cabin that maintained cabin pressure and that would have to be opened first. The air stair was in an unpressurized area of the fuselage beyond that. From what I recall, D.B. Cooper had the pilot descend to an altitude at which the cabin could be depressurized, permitting him to exit via the rear airstair.

That sounds right, thanks!