was nefarious or mechanical, it happened as a result of the transponder and that getting shut off. >> reporter: what is clear, mh 370's captain, not his co-pilot, was the last person on the jet to speak to air traffic controllers telling them "good night malaysian 370." sources tell cnn the sources said there was nothing unusual about his voice which betrayed no indication he was under stress and no third voice is heard. and just today, more than a month after the flight disappeared, we're learning malaysian air force search aircraft were dispatched soon after the airline reported its plane missing. malaysian sources told cnn, headed for the strait of malaca and the south china sea. officials had initially focused the search on the south china sea. there were indications that the