Accident Overview
On November 25, 2019, at 1052 Pacific standard time, a General Atomics Aeronautical Systems (GA-ASI) MQ-9 unmanned aircraft system (UAS), registration N341HK, sustained substantial damage after departing runway 26 during landing at Gray Butte Airport in Palmdale, California. The flight was operated by GA-ASI as a routine training flight for a pilot and sensor operator, conducted under 14 CFR Part 91 and an FAA Certificate of Authorization. There were no injuries or damage to other property.
Weather Conditions
At 1058 PST, the automated surface observation system at Gray Butte reported clear skies with wind from 260 degrees at 18 knots, variable between 220 and 290 degrees, and a peak wind of 270 degrees at 28 knots.
Events During Landing
According to the operator/manufacturer, the student pilot was flying the approach. The aircraft touched down at 79 knots indicated airspeed (KIAS) with a left crab of approximately 5 degrees, consistent with a 7-knot crosswind component from the left. Upon touchdown, the aircraft began drifting left with the nose wheel off the ground. Over the next 15 seconds, increasing right rudder was applied, but the drift continued. The pitch stick position was +9 degrees, with pitch trim set to -5 degrees, resulting in a pitch command of +4 degrees—2 degrees above the recommended pitch in the Flight Manual. The throttle was not moved to ground idle or reverse. A go-around was initiated, but the aircraft departed the runway before the engine could respond.
System Examination
Examination of data logs by the operator/manufacturer revealed that the autopilot prioritizes pitch control over yaw control for movement of the ruddervators. The atypically high pitch command limited the ruddervator authority available for yaw control. With ruddervators saturated in pitch, yaw authority from the ventral rudder alone was insufficient to effect a right yaw. The flight manual did not contain information about the possibility of pitch control prioritization resulting in limited yaw authority.