I like the idea of bunk beds. Instead of 3 people sitting next to each other let them lie above each other. Being able to sleep during long flights would make my life much better.
People typically need to be facing/laying along the axis of flight for the seatbelt to work. If you're laying at 90 degrees and there's a big (de/a)cceleration and you have a belt across your waist, you get folded in half hanging off the bed.
If you stack three people on top of each other then the you need egress (space one one or both sides of the beds) which takes up a bunch of space to get back/forward. Most seats have the aisle as egress but you need more mini-aisles for bunkbeds. You might want to divide it and say some people have egress forward and some backward to save the space... but if there's some kind of emergency you want people to be able to go whatever way they want.
If you think about roughly the volume of 3x3 seats (9 pax) then roughly speaking you could have three sets of three bunkbeds. But the curvature of the airframe means you don't have the same height near the window you do in the middle of the plane, and you may take away cabin baggage space. One way to get around this is to make the lowest bunk very low, like an inch off the deck, but that would mean a smaller market as you have to have pax who can get down low or climb up to the top.
All of this is assuming you're trying to go for the same kind of density of pax as a plane has today. If you just want two bunks and charge more, or you want to have a seat and a bunk (so you sleep only half the flight or something then someone else gets the bunk...) then the space requirements all change. You can also just have some bunks or just in the middle rows on a widebody and on the outside have seats.
Lastly, my memory is the flight computers will try to direct smaller aircraft movements in the vertical axis / pitch angle. Again from memory, but people get really sick if they have a bunch of movement side to side or at some other funny angle their vestibular system isn't used to. And with bunkbeds you might not have a window to look out of for a frame of reference to help. This is another constraint on how you lay people out on the plane.
It's all fixable kind-of but not just "put in a bunch of bunkbeds and make the same amount of money / same price per seat-mile". Someone with more knowledge can probably list all the reasons the FAA wouldn't allow it.
I still want bunkbeds though.
I thought airplane seatbelts during cruise were more about controlling vertical movement than horizontal movement. At least, the strongest sudden accelerations that I've experienced under those conditions, and the strongest ones that I've heard about, were vertical.
Perhaps elderly and disabled people might have an issue during braking but most people wouldn't have any issues I don't think.
They put an extra 40 seats on a plane, increasing from say 180 to 220 in economy, because they expect to sell them
If you want a seat and a bed, that's possible. Buy first class.
If you want a seat that changes into a bed, that's also possible - but business.
If you want a seat that has more legroom, more width, and better food, buy premium economy.
If you want the cheapest way to safely travel, buy economy.
Just don't expect a tesla roadster for the cost of a Citroen c1
Only during takeoff and landing. During level flight you want the seatbelt to prevent upwards motion.
So sign me on for bunk beds.
[0] https://c8.alamy.com/comp/E87ARA/upper-class-on-a-virgin-atl...
Check the table on this page for a list.
They looked not promising but they were surprisingly comfortable for even two or three day rides. You could either sit or lie down on them.
A modern airliner probably wouldn't go for plywood but if the safety aspects could be worked out the general design would be a big improvement for long haul flights.
Evacuation would be a problem though, especially for people crawling out of the bottom bunk. I've always assumed the evacuation problems were the reason this has never happened.
It's really neat, because if you're travelling in a group and don't want to go to bed right away you can fold the top beds up and use the bottom beds as comfy benches.
The problem with putting the same thing on an airplane is that it needs a lot of space. Seats offer way more density than bunk beds.