Damn. So many spy thrillers ruined.
But how did D.B. Cooper do it?
Totally wrong. Not a crazy thought at first glance, but not the way it works.
The goal is to keep the cabin as low as possible as long as possible. And to always climb and descend the cabin interior slowly regardless of the aircraft maneuvers. Different aircraft have slightly different limitations and logic, but the big idea is as above.
The usual method is that after takeoff the pressurization controller climbs the cabin at ~500 feet per minute (FPM) while we’re climbing, but pauses whenever we level off. So as we climb at ~4000 FPM down low decreasing to ~1500 FPM at near cruise, the cabin altitude is lagging behind the aircraft altitude and the differential pressure (inside vs. outside) is slowly increasing. The goal is to get to the maximum differential pressure about when we get to 20,000 feet. The max differential is generally ~8.5 psi for most airliners. Which puts the cabin around 5000’ at that point.
Then as we climb further the system holds that max differential pressure. The cabin will reach 8000’ if and only if the aircraft climbs all the way to its service ceiling in the high 30,000s or low 40,000s.
On the way back down the cabin descends at 300 FPM. Descents are much harder on the ears than ascents, so that’s why the rate is slower. It’s descending continuously with an eye to getting down to the landing airport altitude which it knows. During descent it’ll be limited to not exceeding max differential. So if we start down then level off after a couple minutes it’ll have to stop descending the cabin.
The more typical case is where we descend uninterrupted to mid altitudes then pause awhile and then step down from there to landing altitude with a bunch more pauses along the way. During that first phase of the descent it’ll get down to a pretty low altitude and then just sit there as we bring the airplane down stepwise to meet where the cabin already is.
So in normal flight a CYPRES device would never see anything it’d recognize as a freefall descent. If it’s simply programmed to fire at 1000 feet above the landing altitude, it’d probably see that when we’re at around 12000’ on the descent ~40 miles from the airport.
If we did an emergency descent but still had full normal pressurization throughout, odds are the cabin would be coming down more like 1000-1500 FM to remain below the max diff pressure limit.
Conversely, if we were in cruise and suddenly lost all cabin pressure (e.g. a door blew out) there’d be a very rapid (handful of seconds) climb of cabin altitude up into the 30s or 40s where we are. Meantime we’d start the emergency descent and real quickly the cabin would be at ambient and descending at the same rate we are. Which is 6000-8000 FPM up high decreasing to 4000-6000 FPM in the mid-teens.
Naturally at those high altitudes, the barometric pressure change per thousand feet is much less than the same altitude change at the low altitudes where a sport parachute device is calibrated. But I’d be that sometime during that plummet the device would get the idea it’s descending pretty fast.
Emergency descents end with a level off at 10,000 or higher if needed to clear terrain. After that we go find an airport. We’ll try to keep the aircraft and hence cabin descent rate under 1000 FPM from this point forward. That may not always be practical. We’d try *real hard *to keep it below 2000 FPM.
I’ve ferried an airliner with inop pressurization. It was a real pain in the ears. I have no doubt that sustained 2000 FPM would bust at least one eardrum amongst the 150 laypeople in various states of health in the back.
LSLGuy: The Cypres is programmed to fire at 750 ft. if the rate of descent exceeds 78 mph (or 6864 FPM if I did my math right). Cite
Hopefully you’re not descending that fast at that altitude!
If we’re descending that fast at that altitude we’ve all been doomed for probably 10-20 seconds already. At approach speeds that would correspond to roughly a 30 degree dive. The parachute isn’t going to help much.
A typical aircraft descent speed at that point would be about 700 FPM. With cabin rate of descent zero.
This would seem to need a diagram by R. Goldberg. 
Thanks!
Regarding parachute release, my understanding (I believe from my brother, who skydives or used to, and loved freefall) is that these days you grab a pilot chute and toss it, rather than any complicated mechanism, due to the simplicity and safety (and possibly expense as well). IIRC, he explained that to me after I’d seen a movie where I saw someone do that and thought it odd that there was no “rip cord”.
What’s the SD on that? Do these types also have a CYPRES or other automatic release in case of unconsciousness? Or am I just mistaken about what I was told about the modern manual release?
Your brother is correct, most sport skydiving rigs don’t have a ripcord on the main parachute. The pilot chute is stored in a little pouch on the bottom of the container (backpack) and thrown into the airstream at deployment time.
Most reserve parachutes (all sport rigs have two canopies) use ripcords with spring-loaded pilot chutes. The Cypres is attached to the closing loop on the reserve parachute so the main canopy is not involved.
I thought the exact same thing when I typed it out!
Yeah, my thanks to LSLGuy as well.
I’ve read/thought through that a few times. I’ll be on a flight later this month and will be thinking about what’s going on.
Going back to the OP …
I suspect the pyrotechnic in a CYPRES device is itself a prohibited hazardous material. As are propane tanks, fireworks, ammunition, car batteries, and all the rest of the flammable and corrosive stuff folks try to carry on every day.
TSA is tangentially looking for all that stuff too, and not just because of its potential use as a hijacking weapon.
Prior to this thread I never considered that a reserve 'chute would have an auto-opener nor that the opener have a pryo unit in it. I have no clue whether TSA officially knows this either.
Valgard mentioned that his CYPRES came with a card to show to TSA explaining what it is. Here is the CYPRES page about traveling with the device. The text beginning “Here you see…” is on the card. They claim the device is approved and not subject to any travel regulations. I notice the card doesn’t mention the pyrotechnic charge.
They were provided by the FBI as one of his demands. He asked for four parachutes, two primary and two reserve. It didn’t matter though, in those days you could carry a duffle bag full of koala bears and bombs on board and nobody was checking.
Unless the airframe disintegrates, it’s going to be small comfort when your chute deploys during an uncontrolled descent.
And I believe one turned out to be a training unit, not intended for actual jumps. Accident? So says the FBI. I don’t think it’s clear which one he might have used. IIRC, all four chutes were gone when the plane landed.
Whuh? What’re the possible reasons?
He went out the old back door that planes used to have. He may have just dragged them all back there and the ones he didn’t use just fell out. Maybe he held onto all of them in case some were rigged by the FBI. You gotta admit the guy had giant gonads, and if he actually did survive it’s hard to question his actions.
As close as I could find: Imgur: The magic of the Internet
