updated 1/13/2010 2:28:02 PM ET 2010-01-13T19:28:02

If the so-called Jockstrap Bomber had detonated his device, would it have brought down the airplane? Among the many unanswered questions about the plan followed by Umar Farouk Abdulmutallab are several involving his position in seat 19A, a window seat in the left side of the cabin. Two questions, particularly: Did he get to choose that seat and, if so, why?

If you wanted to bring down the Airbus A330 with a compact explosive device, like the one embedded in Abdulmutallab’s underpants, you would try to hit the most vulnerable part of the airplane. Al Qaeda’s technical planners have proved themselves experts in the detail of aviation operations. Their training of the 9/11 hijackers was just enough to equip them with the skills to fly an airliner precisely into targeted buildings. They would surely have studied the architecture of the Airbus to decide where a bomb would be most effective. And as an engineering student, Abdulmutallab would have been a quick study.

So, in theory at least, seat 19A would seem ideal. It is positioned exactly over the center of the wings, and under it is a tank capable of holding 41,559 liters of fuel. Video demonstrations of a similar amount of the same explosive being detonated in the open show a powerful blast, and that power would be magnified in a restricted space like an airplane cabin.

Detonating the device from that seat would appear to be a three-way bet. It was next to a window and would blow a hole in the airplane’s skin; it would, at the same time, ignite a fire and, if the blast did penetrate the fuel tank then the airplane would explode into a ball of fire.

But it’s not so simple. That center fuel tank is part of what is called the wing box, a structure that anchors the wings to the fuselage and absorbs the greatest stresses of flight. For this reason, it is one of the strongest parts of the airplane. Also, Northwest Flight 253 was in the last phase of a long trans-oceanic flight and the main fuel tank would have been by then very light in fuel. It’s true that even a small amount of fuel would still have been enough to ensure the success of the bomber’s mission, but only if that tough wing box had been penetrated.

The first wave of the blast, blowing a hole in the skin of the fuselage, would trigger what is called an explosive decompression. The cabin air is kept at a pressure equivalent to a height of around 8,000 feet. The higher the flight is, the greater the difference between the pressure outside as the density of the air thins out and the stable pressure inside. It’s this differential that, literally, sucks air out of the cabin in an explosive decompression. But — once again —since the Northwest Airbus was already well into its descent, about half an hour to touchdown, when the attempt to detonate the bomb was made, the pressure differential would have been far less than if it happened at cruise altitude, 36,000 feet.

There are two past events that give some indication that Flight 253 could have survived the bomb. In 1988, a Boeing 737 of Aloha Airlines was cruising at 24,000 feet and approaching Honolulu. Suddenly a huge part of the cabin’s roof ripped away, exposing passengers to sudden decompression. Amazingly, the pilot was able to land. Sixty-one of the 90 passengers aboard were injured, most of them superficially, but one flight attendant was sucked out and fell to her death. (The 737 was old and undetected corrosion had fatally weakened the fuselage.)

Perhaps more analogous, there is the case of TWA Flight 840 that was flying from Rome to Cairo in 1986 when a bomb went off in the cabin-planted under seat 10F, probably inside a life jacket. The blast blew a hole six feet by three feet in the skin of the cabin just ahead of the wings on the right side. The airplane was passing over Greece at the time. Four passengers seated closest to the gaping hole were sucked out, but the rest of the 118 passengers and crew survived. (Nobody has ever been convicted of the bombing but the prime suspect was the Abu Nidal terrorist organization.)

The TWA airplane was a Boeing 727 and, although larger than the Aloha 737, shared exactly the same fuselage. This was an old design, dating from the first generation of Boeing jets introduced in the late 1950s. If those airplanes proved as rugged as they did, then the Northwest Airbus, far more modern and sophisticated in its structure, should have had an even better chance of holding together.

If Abdulmutallab had been instructed to find a window seat in a row over the wings, when and how did he achieve this?  He paid in cash, which means that it was not the kind of online booking where you can pre-select a seat. Also, he had to make sure of getting this seat on the second leg of the flight from Nigeria, the Amsterdam to Detroit leg. Getting to the bottom of his ticketing and seat selection is vital to understanding just how deliberately and skillfully planned this trip was.

There has been speculation about why, having gone into a toilet to rig his weapon, Abdulmutallab did not remain there, where he could not have been as easily detected and subdued by passengers and cabin crew. Toilets are fitted with smoke alarms, but by the time they were triggered it would have been too late.  The fact that he didn’t take this course of action, when it was so easy to do, suggests that his planners knew that the toilets were in a far less attractive (to them) part of the airplane. Instead of a fuel tank underneath, there was a cargo hold. A blast in that location would have, at the very least, caused some kind of explosive decompression, but this would not necessarily have been disastrous.

© 2013 Condé Nast Traveler


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