Date: 201404
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: UAV - Unpiloted Aerial Vehicle
Operator: Military
Operating under: Part 91
Flight plan: VFR
Mission: Test Flight / Demonstration
Flight phase: Descent
Airspace: Class E ZZZ; Special Use ZZZ
ATC / advisory: Military Facility ZZZ
Aircraft component: FCC (Flight Control Computer)
Component problem: Design; Malfunctioning
Reporter organization: Military
Reporter function: Pilot Not Flying; Relief Pilot
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Commercial
Human factors: Communication Breakdown; Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Airspace Violation All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Automation Overrode Flight Crew; Flight Crew FLC Overrode Automation; Flight Crew Took Evasive Action; Flight Crew Returned To Clearance
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: The Unmanned Air Vehicle (UAV) was on descent passing through 3;500 MSL from the west; entering a 45 degree for a mid-downwind entry for right hand traffic for multiple pattern approaches. The UAV's autopilot expectantly switched waypoint tracking logic which contributed to the UAV to penetrate outside its assigned SUA momentarily. The UAV operators were expecting the autopilot to continue to fly straight ahead; make a slight right turn; enter the right downwind on a 45; and initiate the pattern approaches as commanded. The basic autopilot logic will command the UAV to turn the shortest direction to the commanded waypoint in relation to UAV position/heading. As the UAV approached overhead to the recovery site; the UAV's autopilot logic un-expectantly switched from tracking to the commanded waypoint (downwind-to-base) skipped the base-to-final waypoint and began tracking the upwind-to-crosswind waypoint. Since the UAV autopilot skipped the downwind-to-base waypoint and the base-to-final waypoint; the UAV autopilot made the unexpected left turn (shortest distance) to the upwind-crosswind waypoint. The operators notice immediately that the initiated a left turn instead of the predicted right turn. Because of this anomaly; the UAV operators took manual control (autopilot OFF) of the UAV in order to force the UAV to turn right in order to remain within the assigned SUA and in the correct traffic pattern. When the UAV operators took manual control; a link delay caused the UAV to momentary level its' wings before executing the appropriate command. This link delay was also a contributing factor that caused the UAV to momentarily penetrate the SUA. It is predicted that the UAV penetrated 500-750 feet outside the SUA while maneuvering to get back inside the SUA and on course.




Synopsis: A military UAV autopilot unexpectedly switched to waypoint tracking which caused a track deviation outside of special use airspace (SUA) as it entered a Test and Evaluation flight landing pattern so the pilot took remote manual control and reentered the SUA.