No one has come up with authoritative reference for the "preprogrammed turn" that seems to clearly indicate human deliberate action, so I have spent some hours researching. I refer to "news" comments such as CNN:
"Adding to the intrigue, ABC News reported that the dramatic left turn was preprogrammed into the plane's navigation computer. It's a task that would have required extensive piloting experience."
While Foxnews, and others including some posters here, join CNN in that reference, extensive searching suggests it all stems from ABC reporter David Kerley's comment on March 16, ABC ThisWeek, transcript quote:
"KERLEY: The prime minister confirming the report by ABC News the communications gear was deliberately shut down. Now we have learned from a source close to the investigation that whoever was controlling the plane preprogrammed that sharp left turn right off of the flight path, convincing investigators that someone was in control of the jetliner, either a rogue pilot or a hijackers."
No more detail or sourcing information for the above has shown up anywhere I could find. It would be nice if this could be established as fact as it rules both in and out many paths of logic. For now, I personally am tempted to treat it as non-credible, and reluctantly lower my own bias towards an obvious human deliberate cause (a change which started with the ACARS shutting "correction" today from the MH CEO.)