Note: This case was reclassified from an accident to an incident as a result of applicable revisions to 49 Code of Federal Regulations Part 830.2, as amended at 75 FR 51955, Aug. 24, 2010. The case was previously identified under accident number SEA07LA237. Use your browsers 'back' function to return to synopsisReturn to Query Page
On August 24, 2007, at 1228 mountain standard time, a Raytheon Cobra unmanned aircraft system (UAS), N605RN, sustained substantial damage when it collided with terrain in an uncontrolled descent, near Whetstone, Arizona. The aircraft was registered to and operated by Raytheon Company of Tucson, Arizona. The ground-based flight crew was not injured. Visual meteorological conditions prevailed for the 14 CFR Part 91 instructional flight, and no flight plan was filed. The aircraft had departed from a private airstrip used for UAS testing and was entering the traffic pattern for landing at the airstrip when the accident occurred.
According to information provided by the operator, the purposes of the day's flights were to evaluate a software upgrade to the autopilot system, continue evaluation of the automatic takeoff and landing system, and conduct pilot training. Three pilots were involved in the operation: a flight instructor, a student pilot, and a supplemental pilot. Additionally, an observer was present.
The unmanned aircraft can be controlled through a Pilot Console, which is a computer-based interface, or through a Manual Pilot Console, which is a Futaba-based interface. In order to control the aircraft using the Manual Pilot Console, the address of the specific aircraft to be controlled, the "pilot address," is entered using the Pilot Console. Changing the address on the Pilot Console directs the output of the Manual Pilot Console to the specific aircraft. A mode switch on the Manual Pilot Console is used to switch between automatic and manual control of the aircraft.
The accident occurred on the eighth flight of the day. The student pilot, who was being supervised by the flight instructor, was controlling the aircraft using the Pilot Console. The aircraft was placed in an automatic orbit at 6,000 feet msl. During this time, engine runs and ground roll testing were performed on another aircraft. The Manual Pilot Console was used to manually control the other aircraft. All evaluations were completed, and the accident aircraft was readied for landing due to low fuel and approaching rain.
The aircraft was on the upwind leg at midfield heading north at 5,000 feet msl (800 feel agl) when the student pilot commanded the aircraft to "Land Now," to initiate the automatic landing sequence. The flight instructor's attention was distracted from the primary flight display by a request from the observer. At this time, the student pilot noticed that the pilot address for the Manual Pilot Console was still on the address of the other aircraft. He changed the address to the address of the accident aircraft so the supplemental pilot would be able to manually control the aircraft if the autopilot malfunctioned. When he changed addresses, he assumed that the mode switch on the Manual Pilot Console was in the automatic position, which would have resulted in the aircraft continuing the automatic landing. However, the Manual Pilot Console was laying on a table with the switch in the manual position. Changing the address with the switch in manual resulted in an autopilot disconnect. Before the supplemental pilot could take the Manual Pilot Console in his hands and assume control, the aircraft, now in manual mode with the autopilot disconnected, rolled to the left, entered a vertical dive, and impacted the ground. The aircraft impacted about 1/4 mile from the airstrip. There was no fire, and there were no injuries to persons or damage to property.
As a result of the accident, the operator incorporated a software/hardware fail-safe making it impossible to change the pilot address if the mode switch is in the manual position. The switch must now be moved to the automatic position prior to making the pilot address change.