Charlie Brown,
ACARS is an acronym for Aircraft Communications Addressing and Reporting System. It is an electronic messaging system that can be used to send and receive all manner of information to and from an aircraft. When the system first came out it relied on VHF ground stations, with inherent range problems, for it's operation but with aircraft fitted with SATCOM coverage is pretty well global. It can be used to obtain met forecasts, reports, transmit/receive operational info, revised flight plans etc and in conjunction with and electronic maintenance computer transmit a whole variety of engine and other system parameters to a home base central computer for real time analysis. EG Several years ago while en-route to London we were called by our maintenance facility and advised that oil consumption on one of the engines was excessive and we may wish examine the situation. Oil quantity, other than minimum, and so usage is not normally monitored airborne and so the alert from the maintenence boys was appreciated. Hope this helps you out.
Regards,
Bullethead.
