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The background story is a hijacking that happened 1971.

The hijacker, referred to as D.B. Cooper, jumped from a Boeing 727 using the aft airstair. He knew in what air corridor he was (Victor 23, heading south to Mexico from Seattle) and the time. The mount St. Helens (8,365'), was about 10 miles north to him. Portland was 20 miles south. He had however zero visibility of the ground. It was nighttime and raining heavily. I suppose he would not see any lights from Ariel (WA), 10 miles north to his position, and which has a population of about 700 nowadays.

With what precision could D.B. Cooper know where he would fall?

There is another related question, but not a duplicate here: Would a 90 kg object jettisoned from an aircraft create a detectable movement?

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    $\begingroup$ I'm guessing if he was good on charting, had an accurate weather report, knowledge of course planning, and kept good time he could know where he was within a few miles. $\endgroup$ – Ron Beyer Jan 19 '16 at 15:06
  • $\begingroup$ nope. maybe within 300 miles or so $\endgroup$ – doc johnny Oct 9 '17 at 7:11
  • $\begingroup$ Really really depends how familiar he was with the area: if you are e.g. a glider pilot familiar with a certain area you`d know where you are just looking at mountain tops out of the clouds. Then with a compass you could walk in the correct direction to reach a major street. $\endgroup$ – Caterpillaraoz Oct 9 '17 at 7:26
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We have no idea how much he did know, but it's possible he had a basic idea. The fact he came up with the plan at all suggests some kind of aviation background (the air stair, for example, wouldn't occur to many people): so we can probably assume at least some basic navigation ability, especially with how thought out the plan appears to be.

He knew where the aircraft was starting from. He knew the airspeed it would travel at (100 knots, just above stall speed), which would give him a rough idea of how far it had travelled – particularly if he had information about the wind at that level.

Distance = Time x Speed... so all we're missing is the Time. If he knows how long they've been travelling, that's sufficient to allow him to have a reasonable idea of where they are along a known track, particularly if he carried a compass.

It's hard to be sure without the precise weather conditions available, but even in rain then as long as you're below the cloud layer, I wouldn't be surprised if Cooper could see the lights of either Portland or, more likely (considering the angle) Ariel: towns are pretty visible from the air. For example this photo is London from 10,000ft. Admittedly London is quite a lot bigger than Ariel, and the weather is clear, but considering the "closer" areas of the picture are a couple of miles, and the "distant" areas are more like 20 miles away, it's fairly easy to see how even a small town can be quite visible.

London from 10,000ft (source: https://www.flickr.com/photos/andygocher/12836895204)

Note that at 100 knots ground speed the aircraft is travelling at ~2 miles per minute across the ground. I can't find any wind data, but considering the 8:13 jump time was only approximate, it's more than possible that he saw the town below and a mile or two below and behind the aircraft, took a minute or so to prepare, and then jumped when 4-5 miles from the town.

He probably didn't know precisely where he was, but there's a reasonable chance that he saw a town below and that was sufficient for him to attempt the jump. He had the equivalent of over a million dollars in his pocket, he only had to find a town and get on a train in order to escape.

We also have no idea whether he had a chart or similar in his bag, nor whether there was any potential visibility of Mount St Helens (possible, considering the 1/4 moon that night). It's unlikely at 10 miles, but they'd passed it earlier and he may have used it as a point of reference.

In short: he probably had a rough idea of the region (to within 50 miles or so) and quite possibly had just seen a small town.

Did he know what town it was? Probably not, but he likely didn't care either: he had enough money that as long as he survived the jump and walk into the town, it probably didn't matter what the town was.

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  • $\begingroup$ "[H]e only had to find a town and get on a train in order to escape." Yeah, that's not really how the US passenger rail system works (or worked in 1971). If he landed near Ariel, he'd be very fortunate -- only a 20-mile hike to Longview or Vancouver! $\endgroup$ – David Richerby Oct 8 '17 at 19:26
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    $\begingroup$ Also, Wikipedia refers to "extremely limited visibility and cloud cover obscuring any ground lighting below", so I don't think the general assumptions of this answer correspond to the actual situation. $\endgroup$ – David Richerby Oct 8 '17 at 19:35
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While it's impossible for anyone to know for sure it's unlikely he would have had much idea at all of where he was. According to the articles I have read when he jumped it was at night, in heavy rain, and the ground was obscured by cloud cover. The visibility was bad enough that neither of the F-106 pilots which were trailing the airplane saw him jump from the airplane.

He did not direct a specific course, what was agreed was that they would fly to reno to refuel, and then to Mexico. The gear was to be extended and the flaps at 15 degrees, so they could not fly that fast.

Pilots and flight attendant were in the cockpit with the door closed, all Cooper would have had for reference is the outside windows and the view out the back, plus any instruments he brought with him. He didn't have a current weather brief, so no knowledge of the winds aloft and how that would affect ground speed. Given the conditions he would not have been able to see much out of the window at all.

You have to consider human factors as well. The flight was at 10,000ft, unpressurized, and Cooper had been under stress without rest for hours. He had been drinking moderate amounts of alcohol intermittently. All this would have degraded his ability to determine location.

The lack of ground speed data, and exact course meant he would only have a vague idea of his track over the ground, and the poor weather and darkness would have prevented him from using landmarks. He would have had an approximate idea of where he was - somewhere between Seattle and Portland, but other than that he was literally in the dark. He may have spotted the glow of lights from a town and made his move, or he may have deliberately jumped in an empty area to escape. I don't think we will ever know.

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