A method of operating a computerised airline departure control system, the system comprising a central departure control system and a plurality of local departure control systems, the central departure control system being configured to interact with a reservation system, the method comprising: receiving at the central departure control system reservation data for a flight from an airport for at least one passenger from the reservation system, the central departure control system being responsible for controlling departure of the flight; receiving at the reservation system check-in information for the flight, the check-in information being received online; generating at the reservation system a check-in message comprising the check-in information; receiving via a communications interface the check-in message at the central departure control system; updating a status of the at least one passenger to checked-in based on the check-in message; forming from the check-in information a passenger data message for the at least one passenger, the passenger data message comprising information necessary to validate the passenger to which it relates for boarding the flight for which they are checked-in; sending the passenger data message from the central departure control system to the respective local departure control system for the flight; storing the passenger data message at the local departure control system; in response to a data signal or a health signal not being received from the central departure control system for a predetermined period of time, recognising a non-availability of communications with the central departure control system; and on recognition of the non-availability of communications with the central departure control system, assuming, via the local departure control system, responsibility for the flight by providing access to the passenger data message stored at the local departure control system to systems connected to the local departure control system for validation of a passenger boarding pass to which the passenger data message relates, and checking in unchecked-in passengers to the local departure control system after the local departure control system assumes responsibility for a flight. receiving at the central departure control system reservation data for a flight from an airport for at least one passenger from the reservation system, the central departure control system being responsible for controlling departure of the flight; receiving at the reservation system check-in information for the flight, the check-in information being received online; generating at the reservation system a check-in message comprising the check-in information; receiving via a communications interface the check-in message at the central departure control system; updating a status of the at least one passenger to checked-in based on the check-in message; forming from the check-in information a passenger data message for the at least one passenger, the passenger data message comprising information necessary to validate the passenger to which it relates for boarding the flight for which they are checked-in; sending the passenger data message from the central departure control system to the respective local departure control system for the flight; storing the passenger data message at the local departure control system; in response to a data signal or a health signal not being received from the central departure control system for a predetermined period of time, recognising a non-availability of communications with the central departure control system; and on recognition of the non-availability of communications with the central departure control system, assuming, via the local departure control system, responsibility for the flight by providing access to the passenger data message stored at the local departure control system to systems connected to the local departure control system for validation of a passenger boarding pass to which the passenger data message relates, and checking in unchecked-in passengers to the local departure control system after the local departure control system assumes responsibility for a flight.