Reason Foundation’s Poole asks telling questions about the Redundancy that may be needed for NextGen!

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ARTICLE: Retaining Ground-Based Navigation Aids


The words of wisdom of Bob Poole, one of the expert residents at the Reason Foundation, are frequently cited here. Sometimes his thoughts draw some comments in this blog. His recent thoughts about the vulnerability of the NextGen signals to jamming merit republication here. His point that to back up the satellite system by retaining the old, antiquated ground system is devastating to some of the rational for the economics of NextGen.

Here are Mr. Poole’s words of wisdom:

In August, the FCC levied a $38,000 fine on the man whose truck-mounted GPS jammer interfered with the ground-based [GPS] augmentation system at Newark Airport. Jamming like this, mostly from trucks on the adjacent I-95, had prevented use of the GBAS for precision landings at Newark, until the equipment was relocated to avoid the interference.

That incident highlighted the vulnerability of a great deal of the NextGen program to interference with the GPS signals on which key systems such as ADS-B depend. The problem is so large that the FAA has dramatically revised its original plans for NextGen, part of whose business case was to have been the retirement of much of the aging and costly-to-maintain ground-based navigation aids: VORs, NDBs, DMEs, ILSs, and potentially most of the radars (except for enough primary radars for the military to be able to spot and track “non-cooperative” targets).

FAA is now well along on its plan for an Alternative Position, Navigation, and Timing (APNT) system to provide basic navigation in the event that GPS signals are not available. While some decisions are still to be made, it appears that about half of the 1,047 VORs will be retained (and probably be replaced with newer models). All existing ILSs will be kept in operation, rather than being replaced with GBASs. And while NDBs are in the process of being phased out, DMEs are considered essential for both airlines and general aviation in a non-GPS environment. In addition, all secondary surveillance radars (which interrogate aircraft transponders) will be retained, rather than being replaced by the ADS-B system, which means planes will need both ADS-B/Out and their existing transponder. Put it all together, and one whole piece of the cost-savings part of the business case for NextGen has been wiped out.

Because GPS is needed for a vast array of functions in the rest of the economy (including its vital timing signals), an aviation-only solution to GPS vulnerability is quite possibly sub-optimal, as economists would say. Because of this larger concern, the Administration has asked the National Space-Based Position, Navigation, and Timing Advisory Board to assist with a project led by the Department of Homeland Security to update the National Infrastructure Protection Plan. As part of a multi-agency effort, the National Coordination Office (NCO) for Space-Based Positioning, Navigation, and Timing has asked the PNT Advisory Board to monitor the progress of these efforts and advise them on alternative approaches. Brad Parkinson of Stanford University, considered the father of GPS, co-chairs the Advisory Board. He told Inside GNSS that he was alarmed to find that “there are some people, apparently within the federal government, who are talking about GPS in ways that I don’t think are enlightened or constructive.” He told the board about one official who’d encountered the view that “GPS is so vulnerable that it had to be abandoned and replaced—which is a pretty extreme view.”

Under Parkinson’s leadership, an interagency task force in 2007 produced a report examining a wide range of alternatives for backing up the position, navigation, and timing functions of GPS for all users. Its conclusion at that time was that a modernized version of LORAN (called eLORAN) was the best overall solution. But for reasons that have never been explained, that approach was abandoned by the Obama Administration early in the President’s first term. In the past year, however, both South Korea and the UK have begun deploying eLORAN as their GPS backup.

Several aviation experts I’ve been in touch with disagree that eLORAN is best for aviation, and the FAA has a study under way for an alternative to its current plan to retain large portions of its legacy navaids for GPS backup. One alternative is wide angle multilateration (WAM), as recently implemented to provide radar-like aircraft separation in mountainous regions of Colorado. Another might be developed based on a large network of “pseudolites”—such as the system developed by Australian company Locata; its system includes a precise timing signal.

Retaining legacy navaids strikes me as a very poor solution to GPS vulnerability. It’s costly to maintain, provides only basic navigation, and leaves all the myriad other GPS users to find some other solution. Surely we can do better than that.

It is incumbent on Deputy Administrator Whitaker and Assistant Administrator Bolton to explain how the GPS system can be inviolable without the massive expenses of maintaining the ground based system.

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