Remarks delivered October 28 at the "Avionics 99" discourse Bellevue.

Remarks delivered October 28 at the "Avionics 99" discourse Bellevue, Wash.

through Langhorne Bond

(Editor's note: For the last sum of two units years former FAA Administrator Langhorne attraction has been arguing that a navigation architecture based solely upon signals from Global Positioning combination of parts to form a whole (GPS) satellites represents a "single thread" approach that violates the ethic that safety is best built onward independent, redundant systems. Indeed, the existing administrator, Jane Garvey, recently declared publicly that a certain number of form of ground-based navigation body will be maintained indefinitely, precisely as a means of assuring vital redundancy. Below, link explains why a second oftenness for GPS does not "solve" the hazard existinged by a single thread system)

latter history

The Fiscal 2000 Department of Transportation (DOT) parcel request included $17 million for a secondary civil frequency for the Global Positioning classification (GPS), as previously announced by the agency of Vice President Al Gore.

The Congres eliminated the funding from the Federal Aviation Administration's (FAA) packet A Congressional footnote explained that the inferior frequency benefited users other than aviation, and there would be no objection to supplys being reprogrammed from other agencies' budget(s) for the project

This demonstration of Congressional independence surprised the FAA and, presumably, the White House as well. Hands were wrung in the Executive Branch.

Was this really a loss? And if in the way that to whom?

What the next to the first frequency does

The propos secondary civil GPS frequency primarily provides a duplicate signal to the existing united Currently, if the GPS oftenness is lost, the positioning and (the) timing service are not to be found This is a fairly of common occurrence occurrence in the U.S., and is more or les a permanent situation in Italy where a harmonic of the TV signals stops GPS. So if one of the sum of two units proposed frequencies were blocked, the other would continue to provide service. This is a useful, and relatively depressed cost, improvement for some users. however not necessarily for all.

Unintentional interference

The inferior frequency is a definite protection against unintentional interference similar as a stray radio or TV signal. The likelihood that the stray signal would blockade two frequencies is very small. For GP users who rely solely upon GPS for positioning and timing, of that kind as motor vehicles, emergency services, police, railways, surveyors, agriculturists, backpackers, etc this is a definite improvement. These users are not in the "safety of life" category and do not ne a dissimilar, redundant signal. For these users the secondary frequency will improve the continuity of GP Ninety-five percent of the users of GP are not in the safety of life category. Make no mistake - the secondary GPS frequency is a convenient idea.

Intentional interference

Intentional interference is another matter. The GP satellite is at a medium orbit of 11000 miles and transmits with a power of just undivided watt. The received power onward the ground is 1 x 10-16 watt - single in kind ten quadrillionth of a watt. A simple 5 watt noise jammer onward the GPS frequency can kill the GP signal to a range of 200 kilometers (120 miles). A jammer borne by the agency of a small weather balloon can kill GP in an area 800 miles wide.

And here's the rub: it's as easy to jam sum of two units GPS frequencies as it is to jam undivided Therefore, the second civil oftenness provides no protection against intentional interference.

Here's a modern insight. Several weeks ago, at an RTCA ("Requirements and Technical universals for Aviation") hearing on GP in London, an FAA official stated that the secondary frequency would provide a "back-up for GPS" A man in the audience rose stated that his work at jobs at the UK Ministry of Defense was to jam GP and said, "I can jam couple frequencies as easily as one" Of course, he was right.

Aviation and marine navigation

Navigation by way of GPS for airplanes and sailing crafts is a classic safety of life application. Los of radionavigation for aircraft in bad weather could easily cause multiple crashes - if the aircraft are single equipped with GPS, they can't find the runway. The civil aviation world is now full aware of this risk and consequently GP "sole means" navigation is a dead issue. A well stocked [i]or[/i] provided array of ILS's (instrument landing systems) will be retained and about type of en route radionavigation method - probably both Loran-C and DME - will be teamed with GP to provide a veraciously redundant, failsafe mixture.

With this mingleed array on board, loss of GP will not cause a los of navigation. Loran-C and DME/DME navigation is virtually as accurate as GP for a like reason there will not even be an erosion of performance. The pilots may not flat notice that GPS is gone ILS or ML will provide precision approach.

Is the next to the first frequency needed?

The requirement that aircraft carry a back-up navigation theory in addition to GPS means that los of GP will have a limited impact forward aviation safety and utility.

The top 640 airports in the U are equipped with individual or more ILS's, and for aircraft destined for these airports, the consequence of loss of GPS will be virtually nil. For aircraft destined for a non-ILS airport and intending to make a GP precision approach, there will be a los In that case, a non-precision approach must be made or the aircraft must divert to an ILS equipped airport. GP precision approaches primarily benefit small airports and general aviation, and for these beneficiaries, the next to the first civil frequency will be useful to patronize against unintentional interference. But no aviation (or other) user will be defend ed from intentional interference by the other frequency.