"Tauno Voipio" wrote in message
...

There is one fundamental difference to other means
of IFR navigation: It is impossible to test and
approve the GPS signal. For the other NAVAIDs the
station can be measured on ground and fly the measuring
flights and compare the results with the specs in
ICAO Annex 10, and that's it.

Been there - done that.


Why is it impossible to test the GPS signal?