UAV - Unpiloted Aerial Vehicle
Human-Machine Interface; Situational Awareness; Training / Qualification
Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Loss Of Aircraft Control
Aircraft Aircraft Damaged; General Maintenance Action
Aircraft; Human Factors
Once the team arrived in place; we made a short scouting in the search for a good spot for take-off and landing. Unfortunately; the property was almost inaccessible due to very dense vegetation and rocky paths around it. Consequently; we determined that the side of the road was good enough to set the ground base station and run the operations from there. We also made sure that there were no obstacles that could cause us losing the aircraft from line of sight. The weather was sunny with clear skies and the winds were calm. The assigned Pilot in Command was me but I was not the operator of the aircraft. Everything was set to run operations under the FAA Part 107 rules. The crew went through all the procedures to get the aircraft ready for flight; from visual inspection of the components to software system check; while I was thoroughly supervising every step. The mission was to fly autonomously over a specified terrain in a grid pattern; the way points were set on the ground station computer and successfully loaded into the aircraft's autopilot. After testing the control surfaces and motor health; and double-checking a good connection of the aircraft with the remote control; I gave the green light for the execution of the flight. The operator manually took off and flew the initial climb of the flight at full throttle. Once the operator saw that the plane was at a safe altitude for the autonomous mission to start; the operator switched to auto mode while failing to notice that the max throttle was still set. In the next 3 seconds; the operator relaxed his attention and failed to notice the aircraft deviating from the expected flight path. I saw that the plane started to bank to the right and began losing altitude rapidly. I notified the operator of the deviation; but he was unsure how to react. I was close enough to the operator for me to try to correct the deviation by reducing the throttle; which I did but it was too late. The plane was already diving head on to the ground and lost almost all its altitude; and we couldn't do anything else to save it other than killing the motor. The plane crashed not very far from the base station site; it was easily found and recovered. The plane suffered heavy damage to the point that it was not flyable. No collateral damage was found at the crash site.The autopilot was recovered from the plane and I got access to the SD card; in which the log of the flight was saved. The autopilot data showed that all internal components; such as the GPS; pitot tube; radio receiver and power module were within normal range during the short flight. A thorough analysis revealed that both GPS and pitot tube were reading extremely high airspeeds right before the plane went out of control; over 30m/s. The plane is cruise speed is rated at 16m/s; meaning that the plane was going more than double its cruise speed. Given that the plane is a flying wing with unstable yaw tendencies; I believe these tendencies were exacerbated at high speeds and a minor drag differential between the two wings was magnified. This caused the plane to bank and dive in. The autopilot's log also shows that it actually tried to correct this; however because the plane is made out of foam; the control surfaces might have flexed at high speeds; reducing their effectiveness to compensate. The probable cause of the incident was that the operator failed to reduce the throttle before switching to auto mode. A contributing factor was the operator's inexperience in reacting to unexpected situations during the mode transition. Some preventative actions are disable the manual throttle set point feature for the auto mode. This would give the autopilot full throttle control; which would have reduced the airspeed right after switching to auto mode from manual mode. If the manual throttle set point is necessary and is kept enabled; then include a verbal confirmation of proper throttle position by the operator before switching to auto mode. After the verbal confirmation; also have the pilot in command verify and approve the switch. Emphasize the operator to constantly pay attention and be prepared for unexpected aircraft behavior; in particular during flight mode transitions.
A drone operator reported their student lost control of the drone and it crashed.