Everyone who flies knows the scene. Your group is called, you shuffle down the jet bridge, and then you stop. Somewhere ahead, someone is wrestling a roll-aboard into an overhead bin, and forty people wait behind them in a single-file aisle. Boarding feels slow because it is slow, and physicists have spent years working out why.

The surprising answer is that the method most airlines used for decades, boarding from the back of the plane to the front, is one of the worst ways to do it. The fastest method ever measured in a real test looks bizarre at the gate. And the biggest culprit is not the airline at all. It is your carry-on bag.

The aisle is the problem

An airliner has one aisle, or two on a widebody, and every passenger has to use it. When people board in a block, for example rows 20 to 30, they arrive at roughly the same place at roughly the same time and block each other while they stow bags and squeeze into window seats. Everyone behind them waits.

In 2008 the physicist Jason Steffen, then at Fermilab, attacked the problem with a computer simulation. His paper in the Journal of Air Transport Management found that boarding front to back was the worst method and conventional back to front only slightly better. The key, he concluded, is to spread people out along the aisle so that many of them can put their luggage away at the same time.

The Steffen method

Steffen's solution boards window seats first, in alternate rows, starting from the back: 30A, 28A, 26A and so on, then the same seats on the other side, then the skipped rows, then middle seats and finally aisle seats in the same pattern. Passengers are spaced two rows apart, so several can load bins at once without getting in each other's way.

In 2011 he tested it for real. Working with TV producer Jon Hotchkiss, he put 72 volunteers into a mock-up of a Boeing 757 cabin, 12 rows of six seats with a single aisle, at the Air Hollywood studio in California, and timed five methods. The results, published by Steffen and Hotchkiss, were striking: the Steffen method took 3 minutes 36 seconds, window-middle-aisle 4:13, random boarding 4:44, back-to-front 6:11 and boarding in four-row blocks 6:54. Each method was run once, and the authors estimate an uncertainty of about 10 percent.

Footage of the 2011 test of the Steffen method, filmed by Jon Hotchkiss.

The catch is that the method needs a perfectly ordered line. It splits up families and groups who want to sit together, and it copes badly with latecomers. As Steffen told Wired in 2014, no airline had adopted it. He points out, though, that a disrupted Steffen line simply turns into random boarding, which is still better than back to front.

What airlines actually do

Airlines have moved in Steffen's direction rather than all the way. United reintroduced window-middle-aisle boarding, known as WILMA, for economy passengers from 26 October 2023, after tests at about six airports, saying it saves up to two minutes per flight. Premium cabins and pre-boarders are unchanged, and people on the same reservation still board together. Delta switched to eight numbered boarding zones on 1 May 2024, and American now sounds an alert if someone tries to board before their group is called.

Southwest, famous for more than 50 years of open seating, gave it up. It announced in July 2024 that 80 percent of its customers preferred an assigned seat, and assigned seating began with flights on 27 January 2026.

The bags

Every study comes back to the same thing: every roll-aboard lifted over a head is time the aisle is blocked. Analyst Henry Harteveldt of Atmosphere Research Group has argued that airlines should stop charging for checked bags and charge for full-size carry-ons instead. Steffen's verdict is simpler.

CGP Grey on why the fastest way to board a plane feels like the slowest.

CNBC on why airlines have not fixed inefficient boarding.

Sources: Jason Steffen, Journal of Air Transport Management (2008); Steffen and Hotchkiss, experimental test of airplane boarding methods (2011); CBC News; Associated Press; American Airlines; 6abc (Southwest); Wikipedia