MJ
Sadly, without more info, one cannot really take that info as being worth anything. Just because some installation was once certified doesn't mean it's any good. How do you know an aircraft is jamming it? Have you been out with the equipment and detected the jamming, or do you have some inside line to the military?
I've flown in enough planes in which the GPS was nearly falling out of the panel. Yes, I expect it worked just fine once upon a time. Doesn't prove anything.
TNF
That's the same old anti-GPS story you are spreading, without support.
I know it's a waste of bandwidth but people who spread these stories are doing a dis-service to GA.
I do about 150hrs/year, have never seen a RAIM failure, have never been uncertain of position, and this is UK, France, Spain.
Incidentally, and this might really get the anti-GPS crowd going, I have never seen the GPS altitude to be more than 50ft off, in any location where I knew the exact elevation (i.e. on the ground at an airfield). It's also spot on aloft, once one has adjusted the altimeter for the deviation from ISA. Not that I use it for that.