Air Carrier Access Act Technical Assistance Manual (2005)

You must not charge for services that are required by part 382. This means, for example, you must not ask for a tip when providing wheelchair service to a passenger. You may, however, impose a reasonable charge for services not required by part 382, i.e., optional services. Examples of such optional services include medical oxygen for use on board an aircraft or stretcher service. [Sec. 382.57]