Hi, I'm trying to figure out how the fancy 'Aircraft Time Pieces' work . 1.) How do airplane clocks GA and airliner clocks keep track of time? GMT doesn't change in terms of time zones, so that's the time that all other times are measured in relation to. In fact, you could probably just use quartz crystals for this task and then adjust the clock say once every couple of years by a few minutes. I read that in the 777, airplane clocks are sync'd with an atomic clock, but is this the norm in terms of clock designs or is this only used on larger jets? 2.) How does a clock know LT? If you're GA, then you're likely to take off and land at the same airport, so LT is easy in this regard, but if you're flying anything bigger, you're likely to cross time zones. I'm not seeing any wiring connections between the onboard GPS unit and the clock. The wiring diagram to the clock that I'm looking at only has two pins for 'serial data output' and 'serial clock output' but no input, so these things appear to be completely self contained!