"John Bell" wrote in message om...

Other hypothesis are also welcome.

Class B airspace, not category B.

Your simplified definition of GPS, while one of the common ones often espoused
has no basis in reality. This is not how GPS works.

Your information on RAIM is wrong. What is unique about the RAIM used in IFR
approved GPS's is not that it determines when the satellite geometry is giving you
an error NOW, but computes if it will fail while during the expected duration of flying
an instrument approach.