Amid all the discussion about terrorism, one obvious question is rarely asked: why does al-Qaida have a predilection for targeting aircraft when there is a wealth of vulnerable western targets from which to choose?
We have no access to the reasoning of the perpetrators, but it seems safe to suppose that they want to cause as much havoc as possible to as many people and "infidel" countries as possible by the cheapest of means. Crashing a plane fits this double aim very well. International flights involve at least two countries, origin and destination, and the passengers' nationalities typically draw in many more. The borderless nature of the target further encourages fearful inferences in more than just the countries directly involved – if they picked Amsterdam–Detroit, next time they could just as well pick Frankfurt–Miami or Dubai–London – which prompts the introduction of costly new security measures.
As for the means, a small amount of explosive can down a plane and just one person, with little or no military training, can carry out the attack. Attacking flights perfectly embodies the rationale of "martyrdom operations", which – as Ayman al-Zawahiri, bin Laden's deputy, once said – are "the most successful way of inflicting damage against the opponent and the least costly to the mujahideen in casualties". It took four men to kill 57 people in the London underground attack of 7/7; if Umar Farouk Abdulmutallab had succeeded on the flight he took, he would have killed 290 by himself. In the grim maximisation game of terror, that amounts to supreme efficiency.
Yet, that he did not succeed and that all other attempts at attacking planes after 9/11 either failed or were foiled – the shoe-bomber Richard Reid and the five men sentenced recently to long prison terms in London for planning suicide attacks on transatlantic flights – makes those answers to our starting puzzle not quite satisfactory. Why should they keep trying operations that have a low probability of success? Couldn't they pick from the myriad targets in which security is lower or non-existent, often impossible to guarantee? If al-Qaida extended the range of targets, one would think, this would really spread terror and push western security services to breaking point.
My hunch is that a reason to target air travel is precisely because it is the area in which the west has concentrated its maximum overt security efforts after 9/11. Piercing the thick barriers of checks all passengers have to go through to board a plane is in itself a success. It amounts to defying the toughest challenge, freshening up memories of 9/11, showing that even a puny David, farcically armed with just a pair of explosive underpants, can hit Goliath right where he feels strongest.
Umar Farouk Abdulmutallab failed to kill, but succeeded in making the west quake in its boots, engendering a hysterical worldwide security response, shaming the US security services, and inducing Obama to resurrect the dismal and counter-productive rhetoric of "we are at war against al-Qaida", which one hoped had departed with Bush. Had Abdulmutallab succeeded in killing, the global havoc caused would not have been that much greater. He could never have achieved that by aiming at softer targets.