How fast do you estimate the plane was flying at the time he bailed out?
I heard he directed them to fly at 130 with flaps down. Hopefully that is not information that only the perpetrator knows!
What I have read in the past is that Cooper ordered the pilots to fly at 170 knots (very slow speed for a passenger airplane) and the plane was kept at an altitude below 10,000 feet (a low altitude for a passenger plane.)
Cooper obviously knew he was about to jump out so the slow air speed and low altitude makes sense.
I am also assuming that the plane was flying south when he jumped since Cooper ordered the pilots to fly towards Mexico starting from the Pacific Northwest.
Anyways...you might also check out the FOIA released FBI files of D.B. Cooper. There is a lot to read, but you can access them in pdf format at:
http://foia.fbi.gov/foiaindex/dbcooper.htm
More here:
“Mexico City,” he said, and delivered more specific flight instructions: Keep the plane under 10,000 feet, with wing flaps at fifteen degrees, which would put the plane’s speed under 200 knots. He strapped the loads of cash to himself and slipped on two chutes—one in front, one in back—and moved deeper into the vessel, toward the aft stairs, which were used to let passengers disembark from the rear of the plane. The 727 was the only model equipped with such stairs. He lowered them. The seal of the cabin broke, and there was engine noise in his ears and the cold, black, wet windy night outside. He climbed down the stairs and hovered on a plank over southwest Washington. The plane was too high to see anything below. The cloud ceiling that night was 5,000 feet, and some of the most rugged terrain in this country was beneath it: forests of pine and hemlock and spruce, canyons with cougars and bears and lakes and white-water rapids, all spilling out into the Pacific. And then, as the ballad goes,
Out a little service doorway
In the rear of the plane
Cooper jumped into the darkness
Into the freezing rain
They say that with the windchill
It was 69 below
Not much chance that he’d survive
But if he did where did he go?
From: http://nymag.com/news/features/39593/index1.html