Is there any limit on how narrow aisles can be? Sometimes, when I'm flying on the airlines, I'll board an aircraft where the aisles seem incredibly cramped, where it's almost impossible to move past without bumping every seat. I can't imagine how much of a nuisance it'd be for people larger than me! I once saw an obese person a bit stuck between one of the aisles, blocking the way for others to move into the aircraft.

But then I thought about what would happen in an emergency. What if there were numerous large people on board, and there was a fire?

So, are there any limits to how much the airlines can squeeze their planes' aisles?
For a transport category airplane with 20 or more seats the minimum aisle width is 15 inches from the floor to a height of 25 inches, and 20 inches width above a height of 25 inches.


  §25.815
  Width of aisle.
  
  The passenger aisle width at any point between seats must equal or exceed the values in the following table:
  
  
  
  1A narrower width not less than 9 inches may be approved when substantiated by tests found necessary by the Administrator.