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In the Wiki page on "D.B Cooper", the presumed moment he jumped out of the aircraft is described:

At approximately 8:13 p.m., the aircraft's tail section sustained a sudden upward movement, significant enough to require trimming to bring the plane back to level flight.

This was replicated in a test:

In an experimental re-creation, Scott piloted the aircraft used in the hijacking in the same flight configuration. FBI agents, pushing a 200-pound (91 kg) sled out of the open airstair, were able to reproduce the upward motion of the tail section described by the flight crew at 8:13 p.m

What was the likely cause of this? My initial thought was it was his body striking the tail, but that isn't mentioned and doesn't seem to be what happened in the test.

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  • $\begingroup$ Upward movement of the tail, i.e. it's a net pitch down for the aircraft? $\endgroup$ – JZYL Jan 3 '20 at 13:49
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    $\begingroup$ @JZYL, yes, exactly what you'd get if you suddenly shifted the CG forward. $\endgroup$ – Zeiss Ikon Jan 3 '20 at 15:45
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The "sudden upward tail movement" requires nothing more than a sudden unloading of the tail by removing that 90+ kg of man, parachute, and money.

Even with an aircraft as large as a 727, suddenly removing 90+ kg from the tailcone airstair would result in a pretty noticeable shift in trim requirement, with additional tail downforce required to restore level flight. This is especially true when flying at the low speed Cooper had demanded (to allow a more-or-less safe jump).

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    $\begingroup$ @Cloud: You don't make one jump from the rear lav to your at-CG seat, you walk, which is gradual. $\endgroup$ – ymb1 Jan 3 '20 at 13:24
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    $\begingroup$ @Zeiss Ikon Also remember that DB's exit happened at the maximum "lever arm" possible in a 727, so the sudden 90+ kg departure would have the maximum effect on weight and balance. $\endgroup$ – Skip Miller Jan 3 '20 at 15:17
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    $\begingroup$ Based on the evidence available (small portions of the money turning up in creeks in wooded parts of southwestern Washington, as well as the crew report of the sudden tail movement) the consensus among those who aren't conspiracy theorists is that he jumped and either failed to open his parachute, or got hung in trees at landing, and died quite promptly. $\endgroup$ – Zeiss Ikon Jan 3 '20 at 16:25
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    $\begingroup$ Dumping small parts of the money into the environment is exactly what I'd do if I was aiming to cover my tracks. $\endgroup$ – Harper - Reinstate Monica Jan 4 '20 at 16:53
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    $\begingroup$ Cooper was dressed in office attire when the flight left SeaTac -- light clothing and smooth-soled low shoes. Even if he managed to land unscathed in the heavy woods of southwestern Washington, it's very unlikely he could have walked out of that country dressed like that. Now, if he had managed to stash proper survival clothing and gear in the airplane, and load up before he jumped, it's possible he could have survived a successful landing -- but in heavy tree cover, you're more likely than not to get hung up high enough off ground to break things when you cut loose. $\endgroup$ – Zeiss Ikon Jan 6 '20 at 0:27
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When you exit an airplane it shakes quite a bit.
On smaller airplanes it's a lot, on larger it's less but still noticable.

Generally it's not something you aim to do, but I think you can make the shake harder by pushing away from the plane more.

Even though his weight is only a small percentage of the airplanes mass, I'm sure you can notice the shake when someone exits the plane.

And then there is the wind deflected on/back in to the airplane.
As you exit the airplane, very often you deflect back wind in to the airplane which also could enhance the shake.

I don't find it a bit odd that there was a shake and upward movement.

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