14 CFR Part 382 Nondiscrimination on the Basis of Disability in Air Travel (Air Carrier Access Act) (with amendments issued through May 2016)
(1) You may “block” an adequate number of the seats used to provide the seating accommodations required by §382.81.
(i) You must not assign these seats to passengers who do not meet the criteria of §382.81 until 24 hours before the scheduled departure of the flight.
(ii) At any time up until 24 hours before the scheduled departure of the flight, you must assign a seat meeting the requirements of this section to a passenger with a disability meeting one or more of the requirements of §382.81 who requests it, at the time the passenger initially makes the request.
(iii) If a passenger with a disability specified in §382.81 does not make a request at least 24 hours before the scheduled departure of the flight, you must meet the passenger's request to the extent practicable, but you are not required to reassign a seat assigned to another passenger in order to do so.