I remember at the time of the disappearance that a person was explaining that the Rolls Royce engines have/ had their own gps type of data collection on them so that RR can monitor or check in on any of their units basically at any time. These are completely separate from the airframe and some probably don't know they even exist.

He also said that the engines were at diego for a time before the batteries for the device went dead ( or were removed)