Two points:
First, ACARS is not simply a 'maintenance information collection and transmission system'. Broadly speaking, it is a communications and reporting system that is used to transmit all sorts of information to and from the aircraft. That information includes maintenance and systems data that is sent automatically by the aircraft to the airline and airframe/engine manufacturers. The system is also used by the crew and airline personnel to send operational information to and from the aircraft, including operational messages, weather reports, NOTAMS, flight plans and ATC clearances, etc.
Second, although there has been speculation here on PPRuNe that MH did not pay to have ACARS data sent by satcom, I don't believe that has been verified. Indeed, the Malaysian Ministry of Transport's MH370 Preliminary Report states:
'It was later established that the transmissions from the Aircraft Communication and Reporting System (ACARS) through satellite communication system occurred at regular intervals starting before MH 370 departed Kuala Lumpur, Malaysia at time 12:56:08 MYT and with the last communication occurred at 01:07:49 MYT'.
That report seems to indicate that ACARS transmissions were sent via satcom.
Position information is sent automatically by ACARS together with the engineering data. The crew would not necessarily know whether that information was being sent by VHF or satcom. If MH370 was the result of a deliberate act to make the aircraft 'disappear', then I would think the culprit(s) would make every effort to disable any systems that could transmit its position.
Last edited by BuzzBox; 17th Jul 2014 at 23:29.