"It might be unclear to your readers that the WAAS correction, while created from stationary receivers on the ground, is in fact (IIRC) broadcast by a subset of the GPS satellite constellation. Satellite failures can create areas where WAAS isn't available until the constellation is either adjusted or a new satellite is deployed.
I've an IFR certified WAAS GPS navigator for flight, and the accuracy seems generally within centimeters. Awesome performance. The WAAS navigators are also required to have a 5Hz update rate, which allows them to synthesize glideslopes, allowing ILS-like approaches for most airports.
The only problem for aircraft is that Jeppesen is the monopoly provider of GPS databases of enroute and arrival/departure procedures, which now cost ~$450 a year, vs. Free to use the old terrestrial navaids. And Garmin, who couldn't quite get their GPS designs to operate to WAAS standards, were allowed to buy their only competition, UPS Aviation Technologies, to get their hands on a WAAS solution. They stopped development of the UPSAT offering, the CNX80, relabeled it the GNS 480 but never delivered all of the advertised features, used the now Garmin AT office to port the good stuff over to look like the Garmin GNS 430/530 operations, and then quietly announced they were immediately dropping the 480.
BTW there is a free public aviation navigation database, but Garmin is making good money in partnership with Jeppesen and refuses to make the public database available. Not an open format, needs compilation to be usable.
GPS is wonderful and seductive. It is no surprise that general aviation pilots like it a lot and that it has gained a lot of use far faster and wider than the safety community is comfortable with. Many legislators have been clamoring for replacing the aging instrument landing systems used by civil aviation with GPS based systems that could integrate tighter with on-board systems on modern airliners. But there is a big worry about reliability, especially the fact that a small jamming transmitter can very effectively disable GPS within its surrounding area. That sounds far-fetched, but is actually a very real risk.
The trucking industry has embraced GPS for fleet monitoring systems. A GPS receiver with a cell phone modem allows a trucking company to keep track of where its vehicles are moving. This is good for keeping customers informed about whether the load is moving on schedule, but it also allows a degree of supervision over the drivers that bugs many of them out of their skin. They like to think that when they are on a week-long cross-country trek with a load, they are lone warriors on the high range, masters of their own day-to-day life. But the GPS tracking device lets the company know exactly where they have been, and where and when they have been stopping. If they schedule an evening meal break in the parking lot of Gilley's dance hall on Saturday night, it is likely to result in some trouble. Much better for the driver if the device is somewhat unreliable, and fortunately, that can be arranged. Ads in the back of truckers' magazines offer a $30 device that plugs into the vehicle's cigarette lighter socket and transmits pure noise on the GPS radio frequencies. That will disable the GPS devices on the truck, and often all the other GPS devices in a half-mile radius around it. This turned out to be the cause of a lot of malfunctions in an experimental GPS instrument landing system that was being tested at Baltimnore-Washington International airport a couple of years ago.
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