AAIB investigation to UAVE Prion Mk 3, (UAS registration n/a) 181119
Landed short of the runway during autonomous landing, West Wales Airfield, Aberporth, 18 November 2019.
Summary:
During an autonomous landing at a secure airfield without public access, the UAS was in a left turn to line up on the final approach path. The autopilot was programmed to control airspeed with power and glideslope with pitch, so when the UAS started to accelerate and descend below the predetermined descent profile, the power reduced to slow it and elevator was used to pitch the UAS up. However, there was a limit to the amount of elevator the autopilot could command, which was insufficient to return the UAS back to the desired altitude, resulting in it flying into the ground just short of the runway.
Following an investigation by the manufacturer (and operator) of the UAS, the autopilot’s elevator authority has been increased, and the pre-programmed turn onto finals widened and raised to reduce the amount of elevator required during the approach to land.
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