hi,Ive heared about this instrument every now and then but wonder what is it that it does? Is it like an early version of the modern FMS?I need some clarification please.... :-)Andrew

Essentially it is an early generation Inertial nav system. It's very basic compared to an FMS, but one can couple the autopilot to it. A great tool for crossing the oceans out of range of navaids, and I'd imagine the absoute minimum of equipment for regulatory purposes when crossing the ocean. That and they only accept a limited number of waypoints and you need to force DME updates.It's far more manula than a modern FMS is. The 777 uses GPS as it's primary update source for the INS, but supports it with DME where it can.Tim