Steven P. McNicoll wrote:
"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?

It is possible to measure the signal, but it does
not tell anything of the signals of the rest of the
constellation.

We can be pretty sure that an on-ground navaid
station will preform quite like how it did when
measuring it. There is no similar guarantee of
a satellite system controlled by a foreign
authority.

Also, there are no internationally accepted
standards of the GPS signal. For the other
navaids, there are technical performance
requirements in ICAO Annex 10 which is agreed
to be legally binding to all member states.

--

Tauno Voipio
tauno voipio (at) iki fi