On Oct 30, 4:44*pm, macpacheco wrote:

NASA JPL operates a Global Differential GPS system with worldwide
coverage. They claim 10cm performance.

http://www.gdgps.net/

'The NASA Global Differential GPS (GDGPS) System is a complete, highly
accurate, and extremely robust real-time GPS monitoring and
augmentation system'.

I believe the John Deere Starfire commercial service is based upon the
NASA system.

Why can't airplanes use it ?

--- CHAS