Letters

Why only really stupid terrorists would use lasers to take down planes. A response to Patrick Smith's "Ask the Pilot."

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[Read the story.]

I’m a few months away from receiving my Ph.D. in physics from a highly respected physics department. A good portion of my work has involved using various types of lasers.

To understand the improbability of a laser attack, consider the technical requirements involved. A weak laser beam can indeed blind a person. However, hitting a small target like an eye is very difficult over long distances. In order to have a high probability of success the terrorists would need to spread out the laser beam to fill the cockpit window. That isn’t so difficult, but when you spread out a beam of light it becomes weaker, so you need a more powerful laser to compensate. Terrorists would need a large laser with a portable power supply and cooling system. Such systems are available, but they are bulky and expensive.

Next, temporary blindness is certainly dangerous. However, as Patrick Smith pointed out, blinding a pilot for a few seconds is not necessarily enough to bring down a plane. To bring down a plane the terrorists would have to inflict an injury that pilots can’t recover from quickly. That requires either more power or a sustained exposure.

Sustained exposure requires the ability to track a plane. Tracking a moving target is certainly possible, but it would require skilled engineers to develop a system as well as money for parts. To reduce the necessary skill and expense, they would want to illuminate the plane from a point along the flight path. They would also want to do it from a high point that has a line of sight to the cockpit during takeoff or landing. However, takeoff and landing paths are generally chosen for a lack of tall buildings and large hills.

The location requirement is by no means an impossible resource constraint, but it does add to the difficulty of the task. It is interesting that the alleged attacks are happening around the country. Each site would need to be carefully selected, to ensure a good line of sight as well as easy access for bulky equipment and little scrutiny from law enforcement or other nosy observers.

Realistically, the complete weapon system would cost a hundred thousand dollars, require at least two people to operate, and would require considerable time to setup. Not to mention considerable time to dismantle before fleeing. (Unless they want to leave behind expensive equipment that authorities can trace.) And all of this would have to be done from one of the few hills or tall buildings in the flight path.



These are not impossible hurdles for a terrorist group, but most terrorist attacks against America in the past 10 years have involved fertilizer bombs, other improvised explosives, and boxcutter knives. If terrorist groups have money, technological savvy, and a network of operatives to scope out prime sites near airports around the United States, why not do something simple like make conventional explosives and plant them in public places?

Finally, the fact that the alleged incidents have involved visible light makes me even more convinced that these are not terrorist attacks. Lasers that emit visible light would be a poor choice for a weapon system. First of all, pilots would notice that the cockpit was being illuminated and they could cover or avert their eyes while waiting for the illumination to pass. Second, a powerful laser beam passing through the sky will scatter from dust and water droplets in the air, letting law enforcement know where the terrorists are located. Infrared lasers wouldn’t give away the terrorists’ location, and the pilots wouldn’t realize what was happening until it was too late. And infrared lasers are no more difficult to acquire than lasers emitting visible light.

Anything is possible, but this one seems highly unlikely.

– Alex Small

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