A ground-based sense-and-avoid system being prototyped by the U.S. Army would have prevented the mid-air collision of a C-130 Hercules airlifter with RQ-7 Shadow unmanned aircraft at a forward operation base in eastern Afghanistan on Aug. 15, a service official says.
“Had we been operational with GBSAA [ground-based sense and avoid] we would have completely averted the incident,” says Tim Owings, deputy project manager for Army unmanned aircraft systems.
But a software glitch and the recent FAA furlough have delayed Army plans to test the radar-based GBSAA prototype installed at General Atomics Aeronautical Systems’ El Mirage, Calif., training center for the service’s MQ-1C Gray Eagle UAV.
The system uses ground radars at three airports to detect and track aircraft entering a surveillance volume centered on El Mirage when Gray Eagles are transiting through civil airspace to and from nearby restricted airspace used for training.
The first three night-training flights using GBSAA were conducted in April, but a software anomaly on the third flight forced a halt to testing. The glitch has been fixed, but a post-furlough backlog at FAA has prevented tests from resuming, says Mary Ottman, deputy product director for UAV airspace integration.
With 11 hr. of testing complete, another 28 hr. of FAA-monitored testing must be performed before the system can be approved for operational use. This requires the presence of three FAA personnel at El Mirage and is a “big commitment” for the agency, Ottman says, as it works to recover from the furlough.
Investigation showed the radar system was tracking all aircraft as planned, but a program that generates a simulated track to test the system produced an incompatible message. The Army has approved revised software following regression testing using a manned aircraft.
“We began meeting with the FAA in July, and planned to return to flight in August, but then the FAA furlough hit,” Ottman says. Dialogue has resumed since the FAA returned to work, but she does not have a date for a return to flight for the GBSAA at El Mirage.
FAA is working through a backlog of applications for certificates of authorization to operate unmanned aircraft in national airspace that were delayed by the furlough “and we are not the highest priority,” she says.
The C-130 landed safety after the collision with the RQ-7 in Afghanistan, and is repairable in the field, but the incident underlines that “even with procedural controls there is a need for active deconfliction,” Owings says.
Investigation is under way, but “the [Shadow] was where it was supposed to be, doing what it was supposed to,” says Col. Robert Sova, UAV capabilities manager at Army Training and Doctrine Command.
The Shadow was in a holding pattern 4,500 ft. off the end of the runway, where it had been directed by air traffic control, when the C-130 “flew right through,” Owings says. “The manned aircraft did not do what it was procedurally supposed to, nor were they where they thought they were,” Sova says.
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