A military uav autopilot unexpectedly switched to waypoint tracking which caused a track deviation o...

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.

Original NASA ASRS Text

Title: 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.

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.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1167570
Time
Date	201404
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	UAV - Unpiloted Aerial Vehicle
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	None
Flight Plan	VFR
Component
Aircraft Component	FCC (Flight Control Computer)
Person 1
Function	Pilot Not Flying Relief Pilot
Qualification	Flight Crew Flight Instructor Flight Crew Commercial Flight Crew Multiengine Flight Crew Instrument
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 3300 Flight Crew Type 200
Events
Anomaly	Aircraft Equipment Problem Less Severe Airspace Violation All Types Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance Deviation - Track / Heading All Types

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.