"The air travel environment can be overwhelming for most people ... even more stressful for travelers with disabilities. Knowing ahead of time about procedures for boarding the aircraft, stowage of assistive devices including a wheelchair, assistance from the cabin crew, etc., is the key to having a smooth trip", states Terry Moakley of the United Spinal Association.
The United Spinal Association has authored a really straightforward, practical guide to air travel for passengers with disabilities. It is in a question and answer format, and really covers all angles from how far ahead you must be at the airport, to whether you must notify the airline in advance of specific requirements.
Most airlines have medical departments, often referred to as meda desks by those within the industry. They are not only used to determine whether someone is fit to travel let's say after a surgery, but also for items such as oxygen requests.
The pamphlet, Accessible Air Travel: A Guide for People with Disabilities is available in PDF format.
Moakley continues, "Accessible Air Travel is organized in a question and answer format that covers the major provisions of the federal Air Carrier Access Act, as amended, and its implementing regulations. Subjects covered are making reservations, advance notice requirements, seating assignments, security screening, airline liability for adaptive equipment, airport accessibility, boarding assistance, aircraft accessibility, equipment storage, and service accommodations...it also contains important information about complaint procedures for resolving a violation at the airport by a designated airline representative, or more formally in writing to the U.S. Department of Transportation."
What is really helpful too, is that it explains why, for example, some passengers cannot sit in an exit row seat, such as being under 15 or not being able to open the door in case of emergency. Although it deals with regulations in the US, it is pretty universal in terms of the information for most countries. There may be slight differences in other countries, but really it is an invaluable guide for passengers with varying degrees of mobility restrictions or other disabilities.