mh370 ... lost ...day3, page-41

According to http://en.wikipedia.org/wiki/Air_France_Flight_447

Air France Flight 447 automatically transmitted multiple failure and warning messages from its ACARS (Aircraft Communication Addressing and Reporting System) as it went down. All these messages were received by Brazilian air controllers.

So if Malaysia Airlines flight MH370 did a U-Turn and spent 8 minutes descending, before it disappeared off radar, without any ACARS transmissions happening, then nothing was malfunctioning, the decent was controlled and the pilots either couldn't or chose not to communicate.