Technology that will allow pilots to have a real-time cockpit picture of their location relative to near-by aircraft could cost too much to roll out nationwide, says a Transportation Department inspector general report.

The Federal Aviation Administration mandated earlier this year that airplanes carry transponders by 2020 to receive and relay Global Positioning System signals, but the agency hasn't required that airplanes have installed in the cockpit a display showing airplane location relative to other aircraft. Because such a display would require the airplane to not only relay GPS data, but to receive radio transmissions back from ground, it's known as Automatic Dependent Surveillance-Broadcast In. The FAA mandate is only for ADS-B Out, which essentially requires nothing more than aircraft to act as an airborne relay tower for GPS signals for use by air traffic control.

As part of a $40 billion effort to modernize air traffic control called NextGen, the FAA awarded in 2007 a $1.8 billion contract to ITT Corp. for the company to build out a nationwide infrastructure of ADS-B ground towers and infrastructure.

The FAA's theory is that industry will voluntarily equip with ADS-B In displays. But, the FAA's decision to utilize two different ADS-B radio frequencies -- one for for commercial and one for general aviation -- could prevent the nationwide rollout of ADS-B In, the Transportation inspector general says in a report dated Oct. 12.  

ADS-B signals for commercial aviation transmit on a frequency of 1090 megahertz, while signals to general aviation transmit on a frequency of 978 MHz, on a waveform known as Universal Access Transceiver. But for ADS-B In to work in the sense that the cockpit display would show an picture of all near-by aircraft, the FAA would have to rebroadcast ADS-B information. But, doing so would be expensive.

"One FAA official stated that it maybe cost prohibitive to implement [the rebroadcast] nationwide," the report states.

A possibility unmentioned by the report would be for avionics that could receive both the 1090 and UAT signals, but a knowledgeable industry source says that no-one appears to be designing such equipment, so far.

The FAA decided to rely on two separate frequencies in part over fears that ADS-B could overwhelm the bandwidth of the 1090 MHz band, and there's reason to fear that'll occur anyway, the report adds.

"Frequency congestion could particularly impact ADS-B usage in high-density airspace, such as the Northeast Corridor," it says.

The report also criticizes the contracting approach the FAA took with ITT. Under the $1.8 billion contract, ITT owns all the ADS-B infrastructure; the FAA is merely buying it as a service through 2025.

The FAA has said that a service-based contract will save money, but the report is skeptical, noting that FAA cost avoidance estimates have varied by $193 million. The inspector general also asserts that a traditional outright ownership model would have saved $600 million for the first ADS-B segment (there are two segments). The FAA retorts that across the life of the contract, cost savings will accumulate, but the inspector general says that the FAA needs to update its cost estimate before it's due to spend another $2.7 billion on ADS-B by 2012.

In the agency's official response to the audit, Clay Foushee, FAA director of audit and evaluation, said the FAA will update its cost estimate, just not on the inspector general's timetable.

For more:
- download the audit, AV-2011-002 (.pdf)

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