By now you'll know all about the Christmas Flight 253 bomb attempt, and the draconian restrictions in place for in-bound U.S. flights. But do the TSA's emergency regulations make sense, or are they dumbly throwing us back into a pre-transistor era?
The Bomb Technology
Umar Farouk Abdulmutallab, now under detention after being charged with attempting to destroy a passenger aircraft, seems to have attempted to detonate a bomb concealed in the crotch of his clothing. From the (quite sensibly) limited details released by officials, the bomb seems to have been a two-stage, or binary, device with a liquid primary phase based on nitroglycerin, and a secondary explosive phase based on pentaerythritol trinitrate (PETN)--the same explosive used by the shoebomber. Just as in that former case, it appears that the bomb failed due to incomplete detonation.
But how dangerous is this stuff? Very. As noted in a discussion of the tech at the Guardian , just 100g of PETN could blow up a car. Abdulmutallab couldn't have easily concealed enough on his person to blow up the entire aircraft, but just a small amount could have caused a catastrophic decompression--enough damage to maybe tear the plane apart. Secondary damage would then be from the wreckage hitting structures on the ground below.
Could security measures have caught this guy? No, not as currently implemented. The bomb had no metal parts, meaning the bomber didn't set off metal detectors in Amsterdam. The small amount of fluids he needed appear to have passed undetected through the x-ray screening of his hand baggage, or could even have been concealed on (or in) his person. Even the newly imposed and invasive crotch pat-downs wouldn't necessarily have spotted the bomb. The experimental through-clothes radar-based  imaging systems on trial in some airports would probably have been the best solution--but even these may have had difficulties if the bomb materials were small enough. A chemical swab might have detected residues from the bomb chemistry left on the bomber or his effects--but presupposes that he assembled it himself, and that it hadn't been hermetically sealed.
Your Technology on Flights
The TSA's response has been to forbid you to use get up or access your hand-luggage in the final hour of all inbound U.S. flights from elsewhere--an amazingly restrictive and inconveniencing maneuver. At no point in the flight is the in-flight entertainment system to transmit GPS data, allow you to use plane phones, Wi-fi Internet access, or show live TV. The crew isn't permitted to point out any U.S. land references when flying over U.S. soil either, so forget "If you look out of the left side you'll see the Statue of Liberty"-type announcements.
This is all designed to deny potential bombers any access to communications with ground-based co-conspirators (presumably for info on timing, instructions or verbal encouragement); to prevent bombers from knowing where they are, and hence where secondary debris could cause most damage; and from accessing components for a binary chemical bomb that ware concealed in different places.
While all of that makes some sense, the last restriction is just dumb: "Passengers may not have any blankets, pillows, or personal belongings on the lap beginning 1 hour prior to arrival at destination." In other words you'll have to be chilled by air-con, ditch you handbag off your knees and put your laptop away. It's also not clear if you'll be allowed to use a laptop on the seat table, and there are conflicting rumors  about being forbidden to use any kind of personal gadgets during the last hour "sterile time" or during the flight at all.
In other words: Welcome to the mid 20th-Century, where your entertainment is limited to books and magazines. Or do these count as "personal belongings" too? A chunky hardback book would certainly be a good place to conceal stuff, no?
These restrictions are good through the end of this month, but there's been no statement on whether they'll continue on--the fear is they will linger, just like those fluid restrictions imposed after the shoebomber (which recently massively inconvenienced me when flying with a baby.) And they are a classic knee-jerk reaction by the TSA, an unthinking, black-and-white case of shutting the stable door after the horse has bolted. And they won't necessarily work.
Just as this bombing attempt leveraged off gaps in previous security rules, so the next one (assuming there is one) will do so off these new rules--no rule-based system, particularly where humans are concerned, is fool-proof. The next bombing attempt will utilize a system the TSA hasn't anticipated yet.
And in the meantime, tens of thousands of passengers are going to be inconvenienced, subjected to scrutiny and questioning, intrusively and intimately patted down (in ways that would almost count as sexual assault should a stranger do it to you outside an airport) and be forced to remain immobile and bored for long periods of a flight. As one innocent Nigerian has already discovered , this elevated stress, fear and loathing aren't a good combination when you're legitimately ill already. Does all of this sound like passengers are being terrorized? Yup, kinda. But by whom?