I kind of doubt this. From what you’ve described, the pressure difference isn’t going to be drastic enough to cause an instant disabling case of the bends (the pressure changes experienced by divers are much larger then the changes someone in an unpressurized cabin would experience).
The standard treatment for the bends is increasing pressure–this would be accomplished handily by the rapid plummet back to earth. So I don’t think the person would be disabled by the bends and I don’t think the person would be permanently harmed. (Going by what you’ve said and what I learned in my certification courses, which admittedly were a while ago).
No arguments with the rest of your (lengthy) post though.
I imagine they would do it the same way paratroopers exit a cargo plane. They hook on to a “static line” that opens their chute as they leave the aircraft. They also use the round chutes instead of the rectangle chutes because they are less menuverable. The end result is each paratrooper (or in this case business class traveler) all open their chutes at regular intervals instead of in a chaotic mess of people falling through each others canopies.
Some other ideas for aircraft rescue devices I thought up:
The “Cluster Bomb” - in an emergancy, the pilot pulls an emergancy release that splits the top and bottom halves of the aircraft like a cluster bomb releasing it’s munitions. All the passengers spill out, attached to parachutes built into their seats.
The Mega-Chute - Basically, the pilot cuts the engines and releases several square miles of silk and space-age polymer. The entire 200 tons of aircraft then gently floats to Earth.
The air bag - Basically, the same principle that the Mars lander uses.
More extensive use of Black Box material - If it’s the only thing that survives the crash…
The Escape Chute - Kind of like "Executive Decision’. Using the same principal as aerial refueling, a chute is extended behind the aircraft and linked to a rescue aircraft. All the passengers slide gleefully to safety.
The Jumbo-Net - Just a big net that the pilot can fly into in emergencies
Self Destruct Devices - As a last resort, the pilot can activate the self destruct device (just like all space ships have in the movies).
Hey…they aren’t any more outrageous than floating across the Atlantic on a seat cushion.
Speaking of useless safety devices in airplanes, I’ve heard it claimed that the oxygen masks which drop down in the passenger compartment overall do more harm than good. The reasoning goes that in the event of a cabin depressurization, the first thing the pilots are going to do is dive to a safe altitude, and by the time the passengers get their masks on and working, the airplane will be in breathable air anyway. Furthermore, it’s claimed that there has never been an incident in which passenger lives have been saved by oxygen masks, but there has been one crash - the Valuejet flight that went down in Florida - indirectly caused by the oxygen generator system (Ok, actually caused by oxygen generator canisters being illegally tranported while charged).
I think you may be stating things a bit too definitely. I’ve been to 32,000’ with just an oxygen mask, and it worked fine. Breathing pure oxygen, you can go to around 38,000’ before the partial pressure of oxygen drops to what it is in air at sea level.
I’ve also been to 28,000’ in a pressure chamber. At that altitude, we took our masks off for 1 minute. At the end of that time, more than half of the 10 people were pretty woozy (the worst were a couple of long-term smokers); none was unconcious. It’s fair to note that we were at rest and 30,000’ is a bit higher, but in freefall there’d be a good chance of reaching breathable altitudes while still conscious.
And while bends are possible, they would not likely be crippling. In cruise, the cabin of a 747 is maintained at a pressure of around 7,000’. Suddenly taking this to 30,000’ is about like a scuba diver ascending 20 ft. You could get some joint “tingles”, but would not be incapacitated. One of the pressure chamber exercises was an “explosive decompression” from 5,000’ to 25,000’. There’s a lot of noise and the air suddenly goes “foggy” and cold, but there isn’t much other sensation.
Let’s say you’re at 38,000 feet when the depressurization occurs. You need to get down to about 10,000 feet. If you descend at 2,000 feet per minute, it will take you 14 minutes to get down to 10,000 feet. Even at 4,000 fpm, it’s going to take seven minutes. It’s been a long time since I’ve been through decompression training so I don’t remember the period of useful consciousness at 38,000 feet; but IIRC it was only a few minutes.
The air pressure inside the cabin is higher than the air pressure outside the cabin (naturally!). So, how is the air pressure going to contribute to holding the doors closed??
Because to open the doors you have to pull them in a bit before they swing out. This is to keep them from being openable at 35,000 feet, for obvious reasons.
Let me see if I got this right: you’re expecting the guy who spread rumors about you at work, the woman who cut in line at the grocery store and scores of others like them, along with the majority who place self preservation ahead of the preservation of others, to carefully line up along a static line and wait their turn as the plane spirals into the earth?
Broomstick, excellent summary and you’re the pilot, but I think you’re missing another problem with having parachutes on planes. I assume that any emergency that leaves the plane as a stable platform for group parachuting would be best recovered from by having the pilots fly it out (right?) With parachutes onboard, the pilots would instead be trying to stabilize a plane while a riot is taking place inside passenger seating. Woudln’t the associated weight shifts get it in the way?
I know I want the answer to this question, but with the best will in the world I can’t make it not sound like an incredibly stupid thing to ask. But here goes …
So why do people get so worried when someone tries to open one of these mid-flight?
And the desperate but doomed attempt to make it not sound like an incredibly stupid question -
Surely its better that you marshall whatever defences you want (air marshalls, groups of passengers to subdue the ne’er-do-well) whilst said ne’er-do-well is attempting something they will not be able to do as opposed to something that might actually cause damage? You never know they may just give up bored and sit down again … :rolleyes:
I just know this is coming back to bite me in the ass
Panic, I imagine. Most people don’t know how the pressure doors work, and don’t understand it’s basically a cork pointing out. If Joe Schmoe sees a guy grabbing at the door, he’s likely to freak out, and in an enclosed space, panic is very very bad. Better to take the guy down for what he might trigger than for what he isn’t going to be able to do.
Besides, the pressure door can actually be opened in flight at relatively low altitudes (don’t remember the exact figure, but I recall it was higher than I expected). A guy who’s going to jump out of his seat and yank on the door at 30k ft isn’t going to succeed, but maybe the same guy would repeat it at (say) 5k ft coming in for a landing, and thus endanger himself at least and potentially the aircraft.
I refer you to an on-line article here discussing effects of high altitude in general. The relevant quote from that page is:
Now, just because you can trigger the bends does not mean you will. And there are additional risk factors to consider, such as recent scuba-diving (as just one example). But there is no doubt that it is possible, and that possibility is why military pilots intentionally going on high-altitude flights (U-2 and SR-71 as just two examples) “pre-breathe” a nitrogen-free gas mixture prior to take off.
Another article is here specifically discussing altitude-induced decompression sickness, which also includes “bends” symptoms that occur prior to the disabling variety but are nonetheless to be taken absolutely seriously.
Risk factors - Altitude:
Age - there is some indication that risk increases with age. Keeping in mind that the standard dive tables were developed by studying male Navy divers 20-25 years of age, they may not apply to gramps.
Temperature - same article says that low ambient temperatures (such as encountered at 30,000 feet) may also increase the risk of bends.
Body fat - the more you have the more nitrogen you have in storage. This means women are, on average, more at risk than men. And the overweight and obese are certainly at higher risk than those physically fit young Navy divers we mentioned earlier.
Alcohol (they serve that on airliners, right?) - increases risk.
What this says is that while a teetotaling 20 year old male athlete with 5% bodyfat is unlikely to experience disabling bends on bail-out, a 300 lb 40 year old woman who’s had a couple martinis may be getting into the danger zone.
And, of course, SCUBA diving:
Keep in mind, standard cabin pressure is 8000 feet above mean sea level - which is precisely why (as my earlier post mentioned) airline attendants receive training to recognize the symptoms of decompression sickness and the airlines have to deal with this several times a year.
And:
It depends. It depends on the severity of the episode, what bodily systems suffer the most damage, and so forth. Also strenuous physical activity after ascent to high altitude (or high-altitude decompression) can trigger a delayed version of decompression sickness, as joint movement can release sudden bursts of nitrogen into the blood stream (this is also discussed in the article). If you land in a wilderness area, you may have to engage in “vigorous exercise” to stay alive.
Decompression sickness can also trigger blood-clotting. Such clots can break loose after other symptoms disappear (or during vigorous exercise) causing all sorts of havoc in the body.
I doubt the entire passenger list in our hypothetical emergency would get the bends, but many may display some symptoms, and a few may have full-blown cases, permanent injury, or death. Descending to higher pressure can potentially stop new damage from occuring, but it will not reverse damage already done.
New Improved Airplane! Now designed to come apart while in flight! — Ya know, this is going to be a really hard sell to the general public…
Oh, gosh - aside from the logistics of folding and packing such a thing… they do have parachutes for smaller airplanes, those under 3 tons. Major problem in development was keeping the 'chutes from shredding upon deployment. Which would be a Bad Thing.
And, oh yes, the landing is survivable. Not “gentle”
Hmmm… well, the Mars landers aren’t 300,000 lbs, more like 300, and they’re bouncing in 1/3 the gravity of Earth… Other than those “minor” details maybe it would work…
The freeways aren’t wide enough. See this classic column by The Master Himself.
Didn’t someone get killed during that manuver in Executive Decision…?
Diving into the heart of thunderstorm would probably be a bad idea, even with an intact airplane. So would descending into areas of heavy icing conditions, particularly if you didn’t have full control of the airplane or full engine power.
Extremely high mountain ranges may impede your downward travel. “Safe altitude” is usally considered 10,000 feet or less - there are plenty of mountains higher than that.
Maybe there’s more, those are just the ones I could think of off-hand.
JohnnyLA already covered the speed of descent issue. You don’t want to descend so fast you lose all control of the airplane, or overstress it when you resume level flight (espeically if you’ve already suffered severe airframe damage) It can take a surprisingly long time to come down, even when you’re desparate and it’s an emergency.
My assumption would be that if the airplane is stable enough to be used as a jump platform yes, the pilots should be able to fly it (or glide it) safely to the ground.
I am quite willing to assume a bizarre emergency just for the mental exercise of it, though.
As for the weight shift problem… I don’t know. You’d need someone like Pilot141 or another person famillar with big jets to get a definitive answer. The effect of shifting a given weight depends on how much it weighs, how much it weighs relative to the aircraft, and how far it’s from the center of gravity. I don’t know if the passenger load of, say, a 747 is a large enough proportion of the total weight for there to be a significant effect or not, or at what point you have to start worrying.
"Ladies and gentlemen, this is your captain speaking. We have reached our cruising altitude and I am now turning off the seatbelt signs. Feel free to-OH FUCK!!!
[QUOTE=Xema]
I think you may be stating things a bit too definitely. I’ve been to 32,000’ with just an oxygen mask, and it worked fine. Breathing pure oxygen, you can go to around 38,000’ before the partial pressure of oxygen drops to what it is in air at sea level.
QUOTE]
Not to mention that everytime you see WWII bomber footage, the crew seems to be getting along fine at 30k feet with just masks. Same for people who climb Everest (about 29000 feet).
"I’ve heard it claimed that the oxygen masks which drop down… do more harm than good. "
“Homer, those are AIRBAGS!!” - Lisa Simpson
Well it makes more sense than 300 ejection seats blasting their occupants into space like confetti.
“Didn’t someone get killed during that manuver in Executive Decision…?”
