[chippy]

The major thing about beds on planes is international safety regulations. Two that I can remember when working for an airline which were introducing beds:

1) The aisle has to be a set width, so you cant stack cabins across the plane.

2) Passengers need to seated and have a seat belt on upon take off and landing.

I think theres another about being able to be belted in if turbulence happens, and be inspectable by attendants. In short, its not as easy as one may think, and its these regulations which complicate things.

[gargravarr]

In a sleeping capsule, passenger's ranges of movement up/down and forward/backward would inherently be more restricted than in a seat. If necessary, a belt could be provided, although it might not be as comfortable because there's no guarantee on where the person's waist will be when lying down.

The way I picture it is replacing seats as they are currently laid out in e.g. a 747 - 3 seats become stacked capsules -> aisle -> 3/4 seats become stacked capsules -> aisle -> 3 seats become stacked capsule. I don't deny that getting into these capsules would be awkward for people with limited mobility, but I do imagine it is within the realms of possibility while meeting safety regulations.