It is a good idea to let the airline know in advance of the exact date and time that you intend to fly. Even if this is not necessary, simply making sure that the airline is ready to accommodate your needs can make a huge difference on the day of your flight.
Generally, 48 hours notice is the minimum time the airlines need.
You should let the airline know well ahead of time, if you need an on-board wheelchair, or if the battery for your chair is classified as hazardous material.
In order to avoid problems on the day of your flight, it is essential that you provide the airline with at least 48 hours notice, if you require the use of medical oxygen, a supply of electricity for a respirator or any accommodations for travel on a stretcher.
Often airlines charge an additional fee for these services. Any additional charges should be reasonable and be non-discriminatory.
If the airline does not receive advance notice, it is not obliged to provide services such these to disabled travellers. Never assume that all your needs can be met on the day of flying, if you haven't notified the airline ahead of time. Always plan as much as possible ahead of time.
There may, of course, be unforeseen circumstances where an airline will not be able to accommodate all the requirements it agreed to provide. Generally, this will be due to circumstances, such as safety reasons, when the original aircraft would need to be substituted with another at the last minute.
All aircrafts built today must provide accessible toilets in wide-body aircrafts. Toilets with disabled access will also be incorporated into the refurbishment of all existing wide-body aircrafts.