Why are there no 2,3,4,5 tier bunk beds on airplanes?

Technically it's entirely possible, and airplane manufacturers release sketches like this regularly. There are three intertwingled main reasons why this hasn't (cough) taken off yet in practice:

1. Airplanes have really tight regulatory safety requirements, including everybody on board being able to evacuate within a certain number of seconds, and this is tested with live drills using real planes and real people. Evacuating fast would be difficult to do with bunk beds, and merely seeing if it's possible would be a very expensive exercise.

2. Major airlines currently make a lot of money by charging $10,000 for long-haul lie-flat business class seats. Introducing flat beds in economy would be unlikely make up for the lost revenue.

3. Bunk beds are only sensible on long-haul flights, which require big, expensive planes, and good local feeder networks to channel people in. This makes it a tough market to break into for a new upstart (who doesn't have that business class revenue to lose) to finance the attempt.

So you need a large airline with no premium seating and a lot of money that they're willing to burn on an exercise that may flop before the first flight. The only ones that really fit the bill are the biggest low-cost carriers like Ryanair, but they're known for penny-pinching, not leaps of faith, so I'm not holding my breath. Air Asia, are you listening?

Some of the problems that airlines and manufacturers will face (just a guess):

• Where do passengers stow their luggage? making compartments for that will lead to less passenger capacity.
• Bunks, such as crew bunks are not certified for take offs and landings. Except for stretcher cases where patients have to be strapped by three belts. I do not think this is doable for all passengers.
• I do not think trains face the same amount/severity of turbulence as airplanes.
• The tube shaped fuselage makes it even harder to design more than 2 tier bunks unlike some trains. It could be doable in larger planes.
• How will the crew distribute the meals? a 3-4 tier service carts? not doable.

Regarding 11 seats across, this is not a problem at all. These 11 seats in a row will be divided by two aisles. The only layout in I can think of is 3-5-3 (Thanks to Nate's comment), making it possible for everyone to jump into the aisle easily.

On the specific issue of meal service, the airlines could copy ancient Roman elite dining practices. See Why did Romans lie down on couches while dining? for a good illustration.

Provide a pillow or headrest that can be raised at the head end of the bed. Add a fold-down tray table. The space for the fold-down tray table could turn into extra bed length for sleeping.

The flight attendants could slide a tray of food onto the table even if it is at shoulder height. Passengers would eat reclining on one elbow, supported by the pillow. The food would have to be finger food or only require a spoon or fork.

I don't think the dancing girl and piper would be provided in economy class.

Some more practical considerations:

1. It will take considerably longer to do a turn around (cleaning) of the airplane between flights.

2. Seats on airplanes have to be certified against turbulence, safety, fire suppression and even floatation.

3. Others mentioned that there is minimum requirements for evacuation of aircraft; but there are other considerations as well. I can only imagine that boarding time will be affected as people try to climb into their beds.

4. What would happen to the inflight entertainment system that many airlines spend millions on?

5. Safety harnesses aren't available or practical for a bed. It is difficult enough for the aircrew to ensure that people are buckled in now, imagine the joy of having to confirm that all three belts are correctly fastened.

6. How would you secure children?

7. In cases of severe turbulence, you can imagine the chaos if you went flying into the bottom of your fellow bunkmate's bed.

8. During the critical phases of flight (take off / descent / landing / taxi) you need all passengers to be as alert as possible and as secure as possible. Can you imagine the chaos trying to get the attention of people as they are laying down?

Good idea, but not practical when scaled.

For the bunks to be safe, they would have to be an enclosed, padded spaces. But then it would feel like being in a coffin. Seats are probably still the "lowest common denominator" when it comes to passenger preferences, on average.