One of the reasons SA was discontinued was that if you knew the coordinates of a base station, you could correct for the error. Are airports not doing this already?

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Quibblingeek an hour ago | parent [-]

Actually, several airports are. So you have normal WAAS and it has a ground segment. Most (new) IFR certified GPS receivers installed in airplanes today are WAAS capable.

To that, you can augment something called GBAS (we used to call it Local Area Augmentation System but switched over to the ICAO name for it). It’s basically a ground station that sits at an airport and corrects for GPS errors where you need it most (airports definitely qualify here and that’s where you need the best GPS performance).

Ultimately, the FAA is going to go 100% GPS and it’ll fall back to the minimum number of land-based sources for redundancy. It’s about cost. The issues with GPS may cause them to push the timeline back and develop plans to mitigate the issue, but they’re too far down this path to stop now.

	▲	entrope 20 minutes ago \| parent [-]
		To meet its integrity budget, a GBAS needs at least triple redundancy, not just a single station. If one has a lot of patience, one can read the details of how it works at https://elibrary.icao.int/product/299828 (along with SBAS, the ICAO name for what WAAS does; the constellations they can augment; GRAS, a weird hybrid between GBAS and SBAS that apparently went nowhere; ILS; VOR; DME; and VHF marker beacons). Annex 10 Vol I probably doesn't say explicitly that triple redundancy is required, because if you had a single receiver with an MTBF of something like 10 billion hours then you could use just that one. This particular 30-foot error should go away almost entirely for future receivers that implement DFMC SBAS or ARAIM.