poorjohn,
I don't know about the ground support magic, but on-wing the engine data is collated via an ACMF prior to transmission (i.e. shared) via ACARS ...
Click on "Transfer" at
Monitoring systems - Rolls-Royce
or read a copy at
http://www.ingenia.org.uk/ingenia/is...e39/waters.pdf
Also extrarcted off the web is the following though the site owner wants $31 for a copy of the proceedings
IEEE Xplore Abstract - The Honeywell on-board diagnostic and maintenance system for the Boeing 777
Avionics have exhibited a phenomenal increase in complexity over the past twenty years. This increase in complexity has brought with it the unfortunate side effect of a significant increase in difficulty of diagnosing the real reasons for a multitude of raw symptoms originating from these complex subsystems. The integrated Avionics Architecture for the Boeing 777 is being designed with an unprecedented attention to fault detection and isolation capability to address this problem. A key element in this effort is an On-Board Diagnostic and Maintenance System (OMS) that integrates two diagnostic subsystems into the Airplane Information Management System (AIMS) cabinets: a Central Maintenance Function (CMF) and an Airplane Condition Monitoring Function (ACMF). The CMF diagnoses faults responsible for flight deck effects that are logged by the crew and facilitates rapid turn-around of the airplane at the gate. The ACMF captures parameters based on predefined trigger conditions for long-term analysis of trends in aircraft systems and the flight crew. It is noted that the OMS constitutes a major evolution of diagnostic systems directed at reducing the operating costs for the airlines.