Auditors question FAA oversight of ADS-B towers


Federal Aviation Administration reliance on the remote monitoring of a key air traffic control modernization technology carries with it the risk of losing visibility into the national airspace system, says the Transportation Department inspector general.

In a report dated Aug. 4, the DOT OIG says the FAA won't certify Automatic Dependent Surveillance-Broadcast ground-tower systems and will rely instead on performance data remotely transmitted by the 800 planned ADS-B transceivers.

ADS-B is the backbone of the FAA-led NextGen air traffic modernization effort, which seeks to largely replace radars with Global Positioning System-derived data for tracking aircraft positions. The effort, estimated to cost at least $40 billion through 2025, faces a number of managerial and technological challenges. Aircraft flying into most U.S. airports must have on board avionics capable of relaying GPS signals to ground ADS-B towers by 2020.

The FAA decided not to certify ADS-B towers because the agency does not in fact own them, the report says. The agency awarded in 2007 a $1.86 billion contract to the McLean, Va.-based company now known as ITT Excelis to build out and maintain the ADS-B infrastructure under a services contract. The towers send GPS signals relayed by aircraft in flight to air traffic controllers; FAA will certify the data but not the ground infrastructure.

FAA officials told auditors the ADS-B signal contains "electronic metrics intended to assure accuracy and integrity." As for the towers themselves, although the FAA will not periodically send technicians to check and test their equipment--what the FAA means by "certification"--the agency will monitor their performance through a system called the Surveillance and Broadcast Service.

But, SBS is already generating more data than FAA staff have time to analyze, auditors say, and as of late April 2011, they were only dealing with data from 335 of the planed 800 ADS-B towers.

"After the first 83 ground stations were deployed, the monitoring system was already generating 1,100 pages of data per month on the reliability of individual system components," the report says.

In addition, auditors question the reliability of SBS monitoring during an ADS-B outage, stating that unless the FAA receives direct performance data from each of the 800 ADS-B towers, it cannot have independent assurance that they are correctly working. SBS data currently is routed through a primary and backup ITT Excelis-operated network hub, the report says.

In response to the audit, FAA officials say they will develop automated capabilities for analyzing SBA data by June 2012 and assign an additional six full time equivalents to the task of SBS data analysis; auditors say only two FTEs have been examining the data.

For more:
- download the audit, AV-2011-149 (.pdf)

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