[rwmj]

In 2011 I took a flight to Boston which happened to be on the same day that William and Kate got married. I don't know if that was the reason, but the flight was almost empty (apparently under 30 passengers on a 737). It was annoying for a couple of reasons: Firstly they didn't upgrade anyone, even though first and business was basically empty. Secondly, the flight attendants were constantly badgering me in case I wanted something, when really what I wanted was a bigger seat and to be left alone. Anyway, good luck on your 1 passenger flight.

[bluGill]

They can't upgrade people on an empty flight without upsetting the balance of the plane. I've been on flights where we didn't leave the gate until people downgraded so the front wasn't overfull. (I was the only person flying economy, first and economy plus was full so everybody was in front of the wings)

[lordlimecat]

I'm having trouble believing that the margins are so close that the position of a 200lb mass on a 68000 lb plane is a significant factor in anything. If true it would suggest that using the lavatories would be a significant event requiring coordination with the stewards and pilot.

[quacked]

30*150 = 4500 lb. There are cases of planes crashing because everyone rushed to the front or the back to avoid smoke.

I know it's not the same as a commercial airliner, but I used to teach hang gliding on the beach and we'd sometimes get a little packed sand in the back of the keel (which is the name for the central bar that the wings were mirrored across). The total weight of the student plus the glider could get up to ~280 lb, and the amount of packed sand would be less than a pound or two, but the flight characteristics of the gliders would change drastically, to the point where we could barely get them in the air.

As another commenter notes below, the few people moving around the cabin is less about control ability and safety than it is about fuel efficiency.

[pintxo]

Actually, for center-of-gravity reasons they (often) cannot reassign seats freely, as the aircraft gets balanced based on the assigned seats. If everyone moves up front, the pilots might get a surprise in how the plane reacts.

[bdamm]

I think this is actually not the case. A Boeing 737 totally empty and in the smallest possible configuration is 61,864lbs. If 20 people move up to 1st class that is less than 7% of the overall weight. With the engines and fuel in the centerline, that represents even less in terms of overall torque change on the center of gravity. The aircraft would adjust for this with the tiniest of movements on the elevator, so small it very well might be in the hundreds of an inch.

It is not about balance.

[pintxo]

Here is an example for an A320neo where LH seems to have resolved the issue by not booking the last row due to GoC issues [1]. So 6 people can make a difference.

[1] https://simpleflying.com/lufthansa-a320-cog-economy/

[technicaldonut]

I think this depends on how full the plane is.

Moving a few people probably doesn't cause an issue if the rest of the plane is completely empty.

If you move 20 people from the right side to the left side of the plane this will probably have some kind of effect.

On smaller regional aircraft they sometimes ask people to move seats to the other side or back to front.

[bdamm]

Moving people left and right has absolutely zero effect on the controlability of the plane, because the ailerons can compensate for much larger movements than that. What it might have an effect on, though, is the overall efficiency with which the plane flies. It is more efficient to have the center of lift and the center of gravity matched, than not.

[rhino369]

>Firstly they didn't upgrade anyone, even though first and business was basically empty.

They rarely upgrade to international first/business because the meals and other perks cost real money. And it'll piss off the people who payed over a thousand dollars for those seats.