Only trouble is, IIRC the Marshalls remember to carry hollow points, which won't pierce the Fuselage. Perhaps this could work if people were allowed to have their guns checked before going on the plane, to make sure they were carrying the appropriate ammunition.

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Even if a round does puncture the pressure vessel, it's not going to be a catastrophic failure. Things don't just blow up that way. Yes, an emergency landing would be called for, but it would be called for in that situation anyway.

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Korgmeister, you should watch the episode of Mythbusters from last season where they tested the "explosive decompression in an airliner" urban legend. It was a full-scale test, using a DC-9 fuselage that was in the process of being scrapped. It was pumped up to the appropriate pressure differential for an airliner at cruising altitude, and they tested shooting out a window with a .45 ACP bullet, which didn't even blow out the window. Likewise shooting a hole in the fuselage. The use of a small bomb to blow out the window generated a violent depressurization, but not violent enough to be dangerous or even make much loose debris in the cabin fly out the window.

To get the catastrophic explosive depressurization they show in Hollywood, they had to use a pound of C4 to blow open a seam in the fuselage skin, which resulted in the entire side and top of the airplane being ripped open.

As it turns out, the total rate at which air can escape through a 0.45" hole in the fuselage of an airliner is roughly equal to the rate at which it is deliberately dumped overboard to prevent overpressurization. (It's easier to control pressure by controlling leakage than it is to control the rate at which engine bleed air is taken into the cabin.) Theoretically, you could actually maintain cabin pressure with a bullet hole in the skin, but I wouldn't want to try.

Yes, air marshals do carry frangible ammunition that shatters upon impact with the aircraft skin (hollowpoints would still punch through the pressure vessel), but it's more to minimize the damage that the government has to pay to repair than anything else.

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I wasn't worried about explosive decompression, I know enough science to be aware that simply would not be possible. Loss of cabin pressure, and the associated risk of oxygen deprivation if people don't get to their masks in time, is nothing to be sneezed at, however.

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As I said, the pressurization system is entirely capable of keeping up with a single .45-caliber bullethole in the fuselage... and you'd be quite surprised by how quickly an airliner can get down below 10,000 feet if the pilot's in a hurry--if he's REALLY in a hurry, he can shed 15,000 feet per minute or more, getting down to the level where you don't need oxygen any more in two minutes or less.

With the automatic-drop masks, getting to the masks in time isn't a serious issue, while one pilot is required to be wearing his mask at all times above 35,000 feet, if memory serves. (Don't have a current copy of the FARs here to check... Jay?)

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