Boarding an airplane should be a simple process. The window seats go on first, starting at the back of the plane, followed similarly by the centers and then the aisles. In practice, this doesn’t work. First, people are unpredictable and some take much longer than others. Second, and more importantly, the airlines have done their very best to mess up the process. Since most carriers started charging for bags, people not only lug on all sorts of stuff which must be stowed, they also do everything they can to rush on first before the available space is gone. Most airlines reward their frequent fliers with boarding priority, which scatters passengers all over the plane, many of them in aisle seats. The mysterious process of boarding by “zones” probably has some logic behind it, but it is largely ignored by passengers seeking to claim a piece of that precious overhead real estate. Chinese mathematicians have studied this problem, analyzing everything from random boarding to assigned seating. They have proposed an optimal algorithm, but in practice it will never work. First, people are unpredictable.

http://phys.org/news/2012-11-mathematicians-airplane-boarding.html