I’ve been able to observe a lot of passengers boarding planes. Based on what I’ve seen, how we board airplanes doesn’t work very well. And based on what I’ve read, it doesn’t make sense either.
All U.S. airlines allow first class, business class, and their most frequent flyers to board before everyone else. In addition, some airlines sell priority boarding for an additional fee. Most airlines board everyone else in the same way: passengers sitting in the very back board first, with more passengers allowed on the plane gradually from back to front.
Monte Carlo simulations have shown this is an inefficient method. Mathematically, whenever a passenger tries to sit down, there’s a 1 in 3 chance that someone will already be seated in that row and have to get up to let the new passenger in – this slows things down. In addition, most of the people boarding are around the same rows and trying to use the same overhead bins so there is lots of congestion in the aisle. This video simulation shows the congestion well:
United Airlines uses an outside-in boarding process which allows everyone with window seats to board first, regardless of row. After that, all people with middle seats board and then all people with aisle seats. United refers to this as “WilMA” (Window, Middle, Aisle).
An episode of Mythbusters showed this process is nearly 50% better than the more common back-to-front because it reduced congestion in the aisles. The downside of outside-in is that passengers sitting together can’t board at the same time. This could be a problem for families with young children which is likely why United allows them to board earlier.
Outside-in is faster than back-to-front but the unassigned seat method used by Southwest Airlines is even faster (but not by much). Passengers board in order of check-in but, since they have no assigned seat, can sit wherever they like. People naturally avoid congestion and navigate to open rows. While the unassigned seat method is slightly faster than outside-in, it leads to lower customer satisfaction scores. Many people, including me, like to know where they are going to sit before they board – especially if they are traveling with others.
The best boarding method might be a debate between outside-in and unassigned seat assignments if not for a physicist named Jason Steffen. Steffen’s method essentially combines outside-in and back-to-front; instead of window seat passengers boarding in any order they want, they board back to front. After window seats, middle and then inside seat passengers board back to front. An episode of the PBS series Making Stuff Faster tested the Steffen method as 25% faster than Southwest’s unassigned seat technique – making it the fastest known method.
There are three boarding techniques which are all significantly faster than the commonly used back-to-front method. So why don’t the airlines switch? It could be nothing more than an unwillingness to change. Or maybe it’s because more and more passengers are paying an additional fee to board early.
What do you think?