Authorising payment cards on a vehicle

A system and method for improving the security and efficiency associated with payment transactions is described. The invention more particularly relates to in-flight authorisation of payment cards used in transactions on that flight. By reducing the amount of data that needs to be relayed to the ground as part of the authorisation process, the system enables a real-time authorisation of the payment card. This is achieved by generating a first message 1 from card details used in a transaction at a POS in a vehicle. This message is typically compressed for efficient transmission. The message is received at a remote processing server 220 where it is typically decompressed, and has additional information added to the message from information stored at the server 220 in order to generate an authorization request. The authorization request 3 is then sent to a clearing house 230 and an authorization code 4 is received back at the server 220. A second message 6, including the authorization code is then sent back to the vehicle. The second message can also be processed to reduce its size for transmission. The vehicle may be an aircraft.