[gargravarr]

I've thought about exactly this. Take a cue from Japanese honeycomb hotels and stack them three high in the place of the current seats - you could get equivalent passenger numbers on the plane, while giving people a safe way to stretch out on a long flight. Correctly designed, they would be safe, possibly safer than seats, during an emergency landing, although I can see getting out in a hurry being a major setback for implementation.

[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.

[throwanem]

You're describing something not wholly unakin to sleeping racks aboard a naval vessel, although no doubt much more comfortable. They are more space-efficient than beds, but less so than seats.

In order to stack hammocks or racks three-high, transversely to the fuselage axis, as I suspect you intend, you need both a large amount of vertical space - eight or nine feet, minimum - and roughly a second row's worth of space between racks, in order for people to get into and out of them. The former requirement can be reduced at the cost of squeezing people unpleasantly together and potentially dismaying claustrophobes; the latter requirement can be eliminated at the same cost, plus that of exclusively end-on entry to and exit from the rack, two-thirds of the time via a ladder.

At this point the only customers you've got left are those fit enough to be physically able to use your service, and also unconcerned about being cheek by jowl with at least two strangers - or, if the racks have sidewalls, unconcerned about spending however many hours in a box too small to sit up in. A lounge might alleviate that concern, but what about the others? And where will people put their shoes? (Do you wear yours into bed?)

The alternative is to compromise space efficiency for comfort, and a lot of airlines already do substantially that with A380s and individual sleeper pods.