Does anybody know why the onboard clock is running ahead of the GPS clock, even though it supposedly takes it's time from the GPS clock?
I'm not claiming to know, but one possibility is that the onboard clock is not running fast. The time displayed on the FMS in GPS monitor mode may be slow because of the latency of the display. The internal time of the GPS receiver is accurate to a micro-mini second, but the actual display may lag behind that some amount because of delays in the system.