A ground support equipment unit for enabling ground crew to support an aircraft video surveillance system from outside an aircraft via a ground connection panel , the unit comprising: a power output connector for connecting a power cable to a power input connector on an aircraft's ground connection panel , thereby to enable external power supply to the aircraft video surveillance system; a rechargeable battery ; characterised in comprising a converter arranged to output AC power at a specified voltage and frequency; an external power connector for connecting an external power cable carrying AC power; a power source selection switch connected to receive power from the converter and the external power connector and which is switchable to route power either from the rechargeable battery via the converter or from an external power source via the external power connector to the power output connector ; a controller configured to switch the power source selection switch dependent on factors including battery status and presence of power at the external power connector ; and an aircraft power status sensor , wherein the controller is adapted to take account of power status in the aircraft , as sensed by the aircraft power status sensor , as a factor for switching the power source selection switch , such that, if the aircraft power status sensor indicates presence of power in the aircraft for the aircraft video surveillance system, the controller is adapted to set the power source selection switch to an open circuit position, but, if the aircraft power status sensor indicates absence of power in the aircraft , the controller is adapted to switch to the rechargeable battery or to the external power source. a power output connector for connecting a power cable to a power input connector on an aircraft's ground connection panel , thereby to enable external power supply to the aircraft video surveillance system; a rechargeable battery ; characterised in comprising a converter arranged to output AC power at a specified voltage and frequency; an external power connector for connecting an external power cable carrying AC power; a power source selection switch connected to receive power from the converter and the external power connector and which is switchable to route power either from the rechargeable battery via the converter or from an external power source via the external power connector to the power output connector ; a controller configured to switch the power source selection switch dependent on factors including battery status and presence of power at the external power connector ; and an aircraft power status sensor , wherein the controller is adapted to take account of power status in the aircraft , as sensed by the aircraft power status sensor , as a factor for switching the power source selection switch , such that, if the aircraft power status sensor indicates presence of power in the aircraft for the aircraft video surveillance system, the controller is adapted to set the power source selection switch to an open circuit position, but, if the aircraft power status sensor indicates absence of power in the aircraft , the controller is adapted to switch to the rechargeable battery or to the external power source. <EOS>