When I first started using my 720, I did not get a position lock. I installed an external antenna and the system was mostly reliable. Lately however, I am not getting a position lock, rendering me GPSless. I have done facory resets to no avail. Sometimes I show no satellites being received (even though I am outside with no interference....basicall, in flight in an open cockpilt.) Sometimes I show plenty of satellites but still the unit is lost. Very frustrating. I love the thing....when it works....