I've had a number of aircraft reporting TCAS traffic at about 4 mile final where there is blatantly nothing on the radar in controlled airspace where I do not believe there was any traffic. One reported traffic in a position which was below gound level!
Is it possible for an interrogative squitter to trigger a reply from a ground reflection?
I sometimes lose some SSR replies due to the angle of climb/shielding of aerials for a number of sweeps. I expect this would also explain the Air Berlin.
I still want to know what stops ground TCAS trials from triggering TA/RAs when they are pumped up to altitiudes above surface.