A mobile device for communicating with aircraft related systems, a device system comprising a plurality of such mobile devices, a system comprising such a mobile device and one or more aircraft related systems, and an aircraft comprising such a device system. According to a device embodiment, a mobile device comprises: a system interface via which the device is connectable to aircraft-related systems including one or more onboard systems provided onboard an aircraft and one or more off-board systems; and a control unit operable in a first mode to communicate, via the system interface, with the one or more onboard systems and operable in a second mode to communicate, via the system interface, with the one or more off-board systems.