> reduce the precision

GPS satellites will not have the hardware to do selective availability in GPS III, which are currently being launched:

* https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_...

This isn't about using GPS as the only navigation aid in an airplane. It's about augmenting the current air traffic system with additional, more accurate data to help manage airspace.

ADS-B doesn't change anything about how a plane navigates. That's still done with a plethora of redundant instruments, all working together.

That is known as Selective Availability and according to the US Government there is no intention of enabling it again [1]. New GPS satellites are apparently being built without the Selective Availability capability [2].

[1] https://www.gps.gov/systems/gps/modernization/sa/faq/#on [2] https://archive.defense.gov/releases/release.aspx?releaseid=...

Isn't low precision something like +/- 15 feet? For ATC, that seems more than good enough when they keep jets a mile+ apart. It just needs to be more precise than radar.

The government claims that they won't enable selective availability any more (which is less useful as a protective mechanism anyway since multi-protocol receivers can use GPS / Galileo / GLONASS / Beidou).

But if SA was enabled:

Before it was turned off on May 2, 2000, typical SA errors were about 50 m (164 ft) horizontally and about 100 m (328 ft) vertically

https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_...

There are also ground based systems at airports which increase reliability / integrity for things like simultaneous parallel approaches. [1] says to within +/- 1m horizontal and vertical.

[1] https://www.skybrary.aero/index.php/Ground_Based_Augmentatio...

I would hope aircraft would have multiband receivers that also support GLONASS, Galileo, and BeiDou. There's also Japan's QZSS and the regional Indian IRNSS.

Probably depends on how old the stuff is.