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.
