Please reread post 47. There are 2 data down link systems. The ACARS does not provide GPS data; only engine parameters. It available to the airlines for free. The AHM is a subscription service. The airline must pay a monthly fee to get the data. It includes GPS data. MAL did not subscribe so they did not get the data.
Thanks for all the very clear and concise information. I am not an engineer, but this is finally making the most sense. My guess is someone may know where it is, but they aren’t talking.
AHM communicates via ACARS (see Boeing Aircraft Health Management brochure).
ACARS is a data communication network, AHM is a set of data communicated on that network.
My understanding is that Boeing gets the AHM data whether or not the airline subscribes to the service. Yours is the first assertion I've read that AHM includes GPS data. Assuming that AHM does include GPS, my comment was just that the GPS data has to come from a plane-board computation, and I speculated that GPS computation might be turned off by the operator of the aircraft.