Is there any limit on how narrow aisles can be?
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.