Commission regulation (EC) 1107/2006 defines the rights of disabled persons and persons with reduced mobility when travelling by air.
Disabled passengers and passengers with reduced mobility are persons which physical and/or psychological state demands individual care and assistance. Depending of the mobility degree and/or sickness, there is a difference between passengers who requires medical documentation upon check-in and passengers who requires assistance through the airport but no medical documentation is required.
In the following there is a document with detail instruction: LINK