FAA Federal Aviation Regulations (FARS, 14 CFR)

The main passenger aisle width between seats must equal or exceed the values in the following table:

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Minimum main passenger
aisle width
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Passenger seating capacity          Less than    25 Inches
25 inches     and more
from floor   from floor
(inches)     (inches)
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10 or less.................................       12           15
11 through 19..............................       12           20
20 or more.................................       15           20
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\1\ A narrower width not less than 9 inches may be approved when
substantiated by tests found necessary by the Administrator.

[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as amended by Amdt. 29-12, 41 FR 55472, Dec. 20, 1976]