The flight was intended to provide a dual check for a pilot to satisfy company and insurance requirements, and to enable a test flight to be carried out, following extensive maintenance on the aircraft. After a normal takeoff, the aircraft made a brief flight to the training area before returning for landing. The landing gear was selected down and normal safe gear down indications were obtained (three green lights and no warning horn). The safe indications were again confirmed during the final approach phase. The aircraft touched down normally on the maingear, but as the nose was lowered, the nosegear collapsed. The subsequent investigation revealed that the nosegear actuator had been incorrectly assembled. The nosegear downlock switch had been adjusted to compensate for the error in the actuator. This resulted in the failure of the nosegear to fully extend to the locked position, while providing a false gear down indication in the cockpit.