What happened
On 18 October 2016, an unregistered Schiebel Camcopter S-100 was participating in a flight trial off the coast of Benbecula in the Outer Hebrides. The mission was designed to demonstrate the transfer of command and control from a land-based station to a ship-based station aboard the SD Northern River.
During the third takeoff attempt from the ship's helideck, the unmanned aircraft immediately pitched upward and began moving rearward. The aircraft failed to gain sufficient altitude to clear a 19-cm high gunwale located approximately 2 meters behind the takeoff position. The resulting impact with the ship's structure damaged the tail structure of the Schiebel Camcopter S-100, causing the tail rotor transmission to fail. The aircraft subsequently spiraled into the sea and sank to a depth of approximately 30 meters. There were no injuries as the aircraft was unmanned.
The investigation
An investigation involving the manufacturer's analysis of the on-board data logger established that the pilot's climb-rate inputs during the accident takeoff were insufficient. While manufacturer procedures for shipboard operations require a minimum climb-rate input of 55%, the inputs for this flight began at 37% and dropped to 7% within 1.3 seconds.
Additionally, the investigation found that the operator applied a rear cyclic command during this takeoff that had not been present during the previous two successful departures. As the aircraft drifted backward without gaining altitude, the operator increased the climb rate to 100% but simultaneously applied more rear cyclic input, which increased the rearward acceleration. The upward heave of the ship at the time of the incident also played a role in the aircraft's inability to clear the gunwale. Data indicated that the conditions required for the aircraft's trim commands to become active would only have been met roughly 0.1 seconds before the collision occurred.
Safety action
Following the investigation, the manufacturer implemented a software update intended to lower operator workload during the takeoff phase. Under the new software, if the aircraft is on the ground and trim mode is active, climb-rate inputs between -50% and +50% will trigger an automatic +50% climb rate command until the trim becomes active. Furthermore, all cyclic joystick inputs are now ignored by the system until the trim becomes active to prevent unintended maneuvers.