Federal officials said Wednesday that LightSquared’s proposed mobile satellite network would interfere with “the majority” of global positioning system receivers and pose dangerous disruption to airline safety systems.

The findings, announced after testing by aviation and defense agencies and other federal officials, added to troubles faced by Reston-based LightSquared, a satellite-based high-speed mobile Internet company backed by Harbinger Capital Partners.

LightSquared has fought over the past year to overcome concerns by military and other government officials that its network would knock out global positioning systems. The Securities and Exchange Commission has informed Harbinger and its founder, hedge fund mogul Philip Falcone, that they could be charged with securities fraud, according to a Friday regulatory filing.

Battling to save its satellite business, LightSquared agreed to use a different portion of satellite spectrum, further away from GPS units. Government officials conducted tests under the new plan and found the network would not significantly interfere with cellular phones.

However, signals would cause “harmful interference to the majority of other tested general purpose GPS receivers,” and separate tests showed “interference with a flight safety system designed to warn pilots of approaching terrain,” according to a statement Wednesday by Anthony Russo, director of the National Coordination Office for Space-Based Positioning, Navigation and Timing.

LightSquared disagreed with some of the findings.

LightSquared CEO Sanjiv Ahuja said the satellite firm will work with the Federal Aviation Authority to resolve interference issues.

But “we profoundly disagree with the conclusions drawn with respect to general navigation devices,” he said in a statement. He blamed GPS interference on GPS devices and not on the company’s proposed network.

“We have taken extraordinary measures — and at extraordinary expense — to solve a problem that is not of our making,” Ahuja said.

The company’s proposed plan to bring 4G mobile Internet connections to the nation has been hailed by the Federal Communications Commission as a way to bring more competition to the wireless market.

But the company’s plan soon ran into trouble when tests by the company and GPS makers concluded that the network would interfere with technology used by everyone from fighter pilots to minivan drivers.

GPS firms and Republican lawmakers have criticized the FCC for granting LightSquared a key permission that would let it transform its network from satellite-only phones to mainstream smartphones.


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