General Atomics MQ-9

Full Narrative

On November 25, 2019, at 1052 Pacific standard time (PST), N341HK a General Atomics Aeronautical Systems (GA-ASI) MQ-9 unmanned aircraft system (UAS), sustained substantial damage after departing runway 26 when landing during a training flight at the Gray Butte airport, Palmdale, California. The flight was operated by GA-ASI as a routine pilot and sensor operator training flight. The flight departed Gray Butte, and was conducted under the provisions of 14 CFR Part 91 and an FAA Certificate of Authorization (COA). There were no injuries or other damage.

At 1058 PST, the automated surface observation system at Gray Butte reported clear skies with wind from 260 at 18 knots, variable from 220 degrees to 290 degrees, with a peak wind of 270 degrees at 28 knots.

According to the operator/manufacturer, the student pilot was pilot-flying and the aircraft touched down at 79 knots indicated airspeed (KIAS) crabbed to the left approximately 5 degrees, consistent with a 7 knot crosswind component from the left. Upon touchdown, the aircraft began drifting to the left with the nose wheel off the ground. Over approximately the next 15 seconds, increasing right rudder was applied as the aircraft continued to drift left. Pitch stick position was +9 degrees (with pitch trim set to -5 degrees, pitch command was +4 degrees, 2 degrees above 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.

Operator/manufacturer examination of data logs systems information revealed that since 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 the ruddervators saturated in pitch, yaw authority from the ventral rudder alone was insufficient to effect a right yaw.

The flight manual did not have any information about the possibility of pitch control prioritization resulting in limited yaw authority.