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FAA weighs in on LightSquared alternate plan

The US FAA says an alternate operational proposal by wholesale broadband provider LightSquared would likely cause timing issues with its terminal, enroute and oceanic air traffic control systems, among other impacts to safety of flight systems.

The internal analysis, dated 12 July, included dire predictions on the impact of LightSquared deploying the baseline dual-frequency operating mode that the US Federal Communications Commission in January had approved, pending a GPS impact analysis. Along with loss of nearly 800 lives as a result of GPS-based safety systems being unusable until a replacement system could be deployed in the 2023 timeframe, the FAA estimates a financial hit of nearly $70 billion in reduced safety and efficiency benefits.

The FCC-dictated GPS impact analysis, prepared by a government and industry technical working group (TWG) over a five month period from February using analysis and actual testing, found that GPS as a navigation and timing source for aviation and other applications would not be possible with a LightSquared network of 40,000 ground stations retransmitting the L band satellite signals adjacent to the GPS band at high power.

In parallel with the final report, LightSquared submitted to the FCC an alternative plan to use less transmitter power and only a lower 10MHz portion of its assigned spectrum, holding off on using the upper 10MHz portion that it planned to operate in tandem until it received "a clean bill of health" from the FCC. Though limiting the frequency band from the baseline system will cut LightSquared's broadband capacity, the company says it had planned to use a single block of frequencies in the first few years of operation anyway. Initial operations, pending go-ahead by the FCC, are planned for 2012.

LightSquared says only 1% of the estimated 300-500 million GPS devices - mostly those used for high accuracy applications -- would be impacted under the alternative proposal. Included in the high accuracy receivers are units that the FAA uses for timing in its air traffic control function.

Critics doubt that number however. "The [technical working group's] aviation sub-group reported that operation in this lower 10MHz channel 'could not be determined definitively to be compatible' with aviation GPS uses," says the Coalition to Save Our GPS. The GPS advocacy group says the TWG's results show that "well over 50% of all GPS receivers tested would still suffer harmful interference from the lower 10MHz channel."

The FAA and others says more analysis and testing is needed to understand the impact on aviation receivers under the alternative plan.

Sentiments from both advocates and critcs are being submitted to the FCC as part of an ongoing public comment period on the technical report. As of 28 July, more than 2,000 comments had been posted.

The FCC plans to end the comment period on 30 July and make a further determination on the LightSquared proposal after evaluating the input.

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