Not cleared to fly: worries about mid-air collisions keep civilian drones grounded.

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SAN DIEGO -- Local governments and unmanned aircraft suppliers look forward to the day when legions of drones can fly over the national airspace to survey fires, spot displaced citizens in a natural disaster or pinpoint criminals in a police investigation.

But for now, unmanned aircraft are still grounded.

The agency that controls the domestic airspace, the Federal Aviation Administration, said drones are not yet ready to conduct such missions.

One of the FAA's primary concerns is that drones lack the ability to see other aircraft and avoid deadly collisions. Agency officials have said drones must have the same ability as manned aircraft to prevent collisions, meaning they must be able to sense potential obstacles, detect the risk of a crash and maneuver well clear.

Equipping unmanned aircraft, or UAVs, with this capability will require new technology and revised policies, said John Walker, chairman of the RTCA special committee 203, a group that advises the Federal Aviation Administration.

RTCA Inc. is a private, not-for-profit corporation that develops recommendations regarding communications, navigation, surveillance and air traffic management system issues.

"There has never been anything as complex" in the aviation world, Walker asserted during an interview.

The unmanned aircraft industry may wait for another decade before civilian drones proliferate in U.S. skies, Walker said. Standards that would allow the FAA to certify drones will likely not be written until 2019, although he views that date as the "worst case scenario."

Concerns about mid-air collisions is just one of the many barriers that still prevent drones from flying in the national airspace.

On the technical side, another challenge is access to radio spectrum, said Basil Papadales, principal with Moire Inc, a UAV consulting firm in Issaquah, Wash.

"Radio frequency is a problem because safe UAV operations depends on having reliable communications when and where it's needed," he told National Defense. "As cell phones and Wi-Fi computers proliferate, the RF spectrum is getting crowded."

Additionally, the UAV industry doesn't have the money to purchase expensive spectrum, Papadales asserted. The industry depends on using military radio channels, but once companies begin operating in domestic airspace, they will have to get their own.

Another impediment to getting drones off the ground is a lack of coordination among agencies and industry groups, said Dale Tietz, president of New Vistas International, an aerospace consulting firm in Austin, Texas.

The FAA is "oversubscribed" and needs help from industry and other government agencies, he said. The Defense Department is working on organizing its own UAV efforts, but has not merged with other agencies to solve these problems.

"Industry and government regulators are not efficiently organized and funded to accelerate access to the national airspace," Tietz asserted.

Papadales believes the impetus is still on the FAA to move faster, and asserted that the agency "has shown no motivation." The problem has been known for more than a decade, but the Defense Department and the FAA"chose to ignore it," he said. "If current policies stay in place, I don't know if there will be a solution."

In the near term, only small, unmanned aircraft are likely to fly in the national airspace, said Walker.

He said the FAA is "in the process of establishing an unmanned aircraft systems advisory rulemaking committee and will ask industry to make recommendations concerning small UAVs." He noted that small drones have been successful in Japan, where they are used for crop dusting.

"You will see small unmanned aircraft systems as the first category that will be used for business," Walker said.

Papadales's company, Moire Inc., predicted in a 2006 study that 96 percent of unmanned aircraft produced from 2007 to 2016 would be small, low altitude drones that fly between 1,000 and 18,000 feet. The demand for small, unmanned aircraft in the military continues to increase as well.

Meanwhile, makers of collision avoidance, or "sense-and-avoid" systems, say that new technology is available now to help move drones into the national airspace and they are prodding the FAA to adopt it.

One company, SAVDS (Sense-and-Avoid Display System) Inc., based in Mountain View, Calif., said it can eliminate the problem of developing complex software for drones by bringing air traffic information directly to their operators. The system, also called SAVDS, combines UAV positional data from the ground control station with data about other airborne objects that is obtained from a ground-based radar, said company chief executive Stanley Herwitz.

SAVDS computations involving the aircraft's position are fed directly to the ground control station that is used to fly the UAV. This method enhances flight safety because SAVDS is displaying the same flight path as seen by the drone pilot, explained Herwitz. When SAVDS identifies potential airborne conflicts between the UAV and radar-detected aircraft, it provides the pilot with a better visual understanding of how to maintain safe separation distances from these other aircraft, he said. "This approach also enables the safe flight of very small UAVs that may not be detectable using ground-based radar. In those cases where the ground-based radar does indeed detect the UAV, the SAVDS software package features algorithms which ensure that the UAV is not computed to be in conflict with itself."

The system uses the Thales/Raytheon Sentinel tactical military radar, which is used by the Army and the Marine Corps. Sentinel is a 3-D radar that was originally developed to alert and queue short-range air defense weapons to the locations of hostile targets approaching their front line forces.

The radar uses an X-band range-gated, pulse-doppler system, Herwitz said. The advanced phase-frequency electronic scanning technology forms sharp 3-D pencil beams covering large surveillance and track volume. Sentinel automatically detects, tracks, classifies, identifies and reports targets, including unmanned aerial vehicles, rotary- and fixed-wing aircraft, and cruise missiles. Sentinel operates at a range of 40 nautical miles.

SAVDS technology is "not a final end-all solution, but an interim fix to fly safely," he said at a Technology Training Corp. unmanned systems conference.

The system is specifically designed for use with small drones that fly under 18,000 feet, Herwitz said. He believes these drones are too small to be affixed with transponders to relay their position.

Small, unmanned aircraft have great potential in civilian airspace, Herwitz said, because they are cheaper than the military's Global Hawks or Predators and they can more closely survey fires, disaster areas or perform agricultural missions.

The company has presented its data to the FAA but was told that radars cannot detect low-metal, slow-moving objects such as hot air balloons or gliders, which makes them unsuitable for the sense-and-avoid requirement. Herwitz disagreed. He tested out his radar system last summer on a hot air balloon and showed that it could in fact detect them. He planned to conduct a glider test this month.

Papadales said radars are a good option for sense-and-avoid because they can see through all weather conditions. But the downside is they take more power and would require drones to have radar antennas. Unmanned aircraft makers would have to figure out where to put them and take into account the issue of added weight, Papadales said.

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Herwitz countered that he developed a system to avoid exactly that problem. His system does not require drones to have radar antennas, he said.

Critics of radar systems also question their high costs. Herwitz argued that once the system is approved, mass production of the technology would drive down the price.

He suggested that one government agency or group purchase a single system and act as a service provider.

Another company, Prioria, based in Gainesville, Fla., has developed a passive, optically-based sense-and-avoid system that can detect both static and moving objects, according to chief executive Bryan da Frota. Prioria's technology was developed for very low altitude UAVs that fly below 1,000 feet.

Included in the system are three handheld drones and one ground station. The aircraft, called Maveric, is affixed with an onboard computer and sensors that have been pre-processed to interpret data and tell the vehicle how to fly, said da Frota. The computer sends information down to the ground station, allowing the operator to send commands back to the UAV.

Maveric has a small, 30-inch wingspan and is made of carbon fiber. Its wings can wrap around the fuselage, which allows the aircraft to be put into a six-inch tube and carried inside a backpack, da Frota said. The company is focusing on micro air vehicles as a starting point and plans to develop technology for larger drones as well. "We want to slowly evolve collision avoidance," he said.

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Prioria first tested its aircraft last July, when it successfully avoided a hedge of trees. The Army purchased one flight system in February for research, da Frota said. Each unit costs $150,000. Other government agencies have signaled interest, but da Frota declined to name them. Some agencies are specifically interested in purchasing the software and integrating it into their drones, he said.