Studies by airlines have shown that the time taken by passengers to stow their bags ranges from 15 seconds to a minute, about 34 seconds on average. Hence the time gap between successive boarding groups should also be about 34 seconds. This results in the first passenger in each group entering the plane just as the last passenger in the previous group has taken their seat.
The flow rate of passengers through boarding pass checking is about one every 2 seconds, so after 34 seconds 17 passengers will have reached their places on the Flying Carpet. Checking is paused while this group moves on, taking about 12 seconds to vacate the Flying Carpet, total time 46 seconds. Checking resumes, another 17 passengers take their places on the Flying Carpet, then move on, etc..
The process is repeated at the rate of one group every 46 seconds, 34 seconds apart (between the first passenger in any group and the last passenger in the previous group). The above figures are averages, based on observations from real-world trials. Group sizes can vary, normally between 15 to 20 (as was the case in the trials), the important factor is to maintain the frequency and time between groups. In round figures that’s one group every 45 seconds, with 35 seconds between each group.
The most objective measurement of boarding is the time between the first passengers entering the plane and the last passenger reaching their seat. Using the above recommended figures, 10 groups @ 45 seconds would take 450 seconds (9 minutes) to pass through the plane door. As there are only 9 gaps, this figure allows 35 seconds for the last passenger to get from the plane door to their seat.
As well as being well-spaced timewise, a group size of 15 to 20 also provides optimum physical space – it’s about the most passengers that can comfortably fit with their bags along a typical aircraft aisle having 25 to 30 rows of seats. Being at random, they won’t all be evenly spaced, but most have plenty of elbow room.
Optimising time and motion in this way achieves efficiency but it also makes it more pleasant for passengers - 35 seconds is the longest time anyone has to wait at any stage, and everybody is aboard in under 10 minutes.