Abstract: A vertical lift fan has a switchable transmission system. The fan includes a lift fan unit having one or more fan rotors. The fan further includes a differential gearbox having an input gear connectable to a transmission shaft for providing power to the fan, and first and second output gears. The first output gear drives the fan rotors. The fan further includes a first brake unit for braking the first output gear, and a second brake unit for braking the second output gear. When the second brake unit is activated and the first brake unit is deactivated, rotational action provided by the transmission shaft is diverted to the first output gear to turn the fan rotors, and when the first brake unit is activated and the second brake unit is deactivated, rotational action provided by the transmission shaft is diverted to the second output gear away from the fan rotors.