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INTHESPOTLIGHT


Ryan Terry, Director of Regulatory Licensing and Policy, Lockheed


Martin Corp. Unstable GPS and scrambled air-to-ground communications due to Ligado interference pose risks to aviation operations.


L


IGADO NETWORKS, THE REBRANDED LIGHTSQUARED, ASKED THE FEDERAL GOVERNMENT FOR permission to repurpose its satellite spectrum licenses so they could be used for land-based mobile wire- less broadband service. But users of the National Airspace System say Ligado’s plan threatens to interfere


with critical services, including GPS and satellite communications, that depend upon interference-free operations in the spectrum adjacent to the Ligado network. As Ryan Terry, director of regulatory licensing and policy for Lockheed Martin Corp., explains, this issue is a threat to aviation safety, particularly to low-altitude operations.


GPS interference in low- altitude environments


affects pilot workload, ADS-B, and other aviation functions used by aircrews for safety.


Why does Lockheed Martin care about radio- frequency spectrum? Terry: First and foremost, Lockheed Martin is committed to the safe, continued use of GPS and related infrastruc- ture. We manufactured the most recent generation of advanced GPS satellites, GPS Block III. So we care about issues that impact users’ access to GPS signals. That’s why the Ligado issue is specifically relevant— testing has shown it’s likely to interfere with that access. Lockheed Martin is also a leading manufacturer of fixed-wing aircraft and, of interest to your readers, a


premier manufacturer of a variety of medium- and heavy- duty performance rotorcraft. We also manufacture and sell a host of unmanned aircraft systems (UASs). These aircraft all rely in some capacity on uninter-


rupted, predictable GPS signals for the safety of their operations, which routinely are conducted across some of the most challenging terrain and in fulfillment of criti- cal missions. Predictable and uninterrupted GPS naviga- tion is essential throughout all of these sectors. We’re also seeing the potential for the Ligado net- work to interfere with satellite communications between


18 ROTOR JUNE 2021


air-to-ground communications for these aircraft. Unstable GPS and scrambled air-to-ground communications: the combination isn’t a good scenario.


What could be the impact if Ligado is allowed to proceed with its plans?


Ligado has said it will erect up to 20,000 cellular towers to build its network. Testing shows that cellular signals from those towers would interfere with aircraft operating FAA-certified GPS receivers. To mitigate this, the FCC is proposing a 250-ft. separation between Ligado towers and aircraft. But this isn’t a workable solution, especially for low-altitude operators using helicopters and UASs. [Editor’s note: see the graphic above right for an exam- ple of how maintaining a 250-ft. distance from a Ligado tower isn’t realistic for aircraft conducting low-altitude operations.]


One major concern we have is the potential impact of


this interference on helicopter terrain awareness and warning systems (HTAWSs), which are critical to deter- mining location, particularly in harsh weather or low- visibility conditions. GPS interference in these low-altitude environments also affects pilot workload, ADS-B, and other aviation functions used by aircrews for safety while operating within 250 ft. of cell towers, which is often necessary in, for example, helicopter air ambulance operations.


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