Title II of the Americans with Disabilities Act (ADA), Section 12141(2), specifically excludes airline travel. Airline travel is instead, covered by the Air Carrier Access Act (ACAA), 49 U.SC. 1374© and regulations implementing the Act issued by the Department of Transportation as 14 CFR Part 382. The ACAA preceded the ADA, and Congress excluded air carriers and other air transportation services from the scope of ADA.
As regulated under 14 CFR 382.87: Seating accommodations (f) "Carriers are not required to furnish more than one seat per ticket or to provide a seat in a class of service other than the one the passenger has purchased."