What if the Christmas bomb had exploded?

Answers to your questions about the news.
Dec. 29 2009 6:21 PM

What if the Christmas Bomb Had Exploded?

Would the plane have crashed?

Underpants bomb.
The underwear in which Umar Farouk Abdulmutallab allegedly concealed explosive material

Rep. Peter King claimed on Sunday that if Umar Farouk Abdulmutallab had successfully detonated the explosive device taped to his leg, Northwest Airlines Flight 253 "would have come down and we would have had a Christmas Day massacre with almost 300 people murdered." Is King right? If the detonation had gone according to plan, would the airliner have crashed?

Maybe not. Abdulmutallab boarded Flight 253 with about 80 grams of the chemical PETN hidden in his underwear. This amount could very well have punctured the aircraft's side wall. According to ABC News, after Richard Reid's failed "shoe bombing" on Dec. 22, 2001, government-commissioned tests concluded that 50 grams of the chemical could have this effect. And in a controlled explosion conducted for CNN, U.K. explosives expert Sidney Alford demonstrated that just 6 grams of PETN can create a large dent in a metal plate twice the thickness of fuselage. (On an Airbus A330, the fuselage is a 0.042-inch aluminum sheet. The aircraft skin itself, including the plastic window, wiring, and paint, is 6 or 7 inches.) But even if Abdulmutallab had succeeded in puncturing the skin, fatalities would not have been inevitable.

In a worst-case scenario, a hole in the side of a plane could lead to a sudden loss of pressure—the cabin may tear open, and passengers may get blown out. The risk of rapid decompression is greater the higher the plane is off the ground and the bigger the gash in its side. But the Airbus A330 had already begun its descent when Abdulmutallab tried to ignite his explosive. And there are instances of aircraft sustaining a large tear without lethal consequences. In July 2008, a piece of fuselage the size of a car fell off the side of Qantas Flight 30, carrying 349 passengers and 19 crew members. After a steep descent from 29,000 to 10,000 feet, the plane landed safely.

There's also no guarantee that the 80 grams of PETN would have popped a hole in the fuselage in the first place. The CNN-sponsored test described above evaluated an unobstructed blast, with the chemical coming in direct contact with metal. In the case of the Christmas bombing attempt, there may have been some interference. Abdulmutallab had a window seat, but he does not seem to have held the explosive directly up against the side of the plane. Instead, it seems he strapped the PETN to his crotch-leg area, then covered himself with a blanket. His body would have absorbed part of the blast.

Had the PETN explosion occurred according to plan and had it penetrated downward, there may indeed have been a "Christmas Day massacre"— seat 19A, where Abdulmutallab spent the flight, is conveniently located about 7 or 8 feet above the fuel tanks.  From Abdulmutallab's lap, the blast would have had to go through his body, the seat cushion, the aluminum and titanium floorboards, and a lot of plastic. If he'd placed the PETN on the floor next to the wall, he would have been more likely to succeed. *

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Explainer thanks Ross Aimer of Aviation Experts and Jimmie C. Oxley of the University of Rhode Island.

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Correction, Dec. 30, 2009: This article originally stated that even if the explosion had reached the fuel tanks, the passengers would have had a small chance at survival, since at the end of a flight, fuel tanks are nearly empty. But fuel fumes in a nearly empty tank can lead to a dangerous explosion as well. There are several variables at work, including how much air is let in through the cracked tank and the resulting fuel-vapor-and-air mixture. So it's not necessarily the case that less fuel is less dangerous. (Return to the revised paragraph.)

Juliet Lapidos is a former Slate associate editor.