If the co-pilot was heard to say, "All right, good night." It begs the question, what frequency? VHF? HF? Satellite? If VHF this would automatically - by line of sight - narrow the search area. As a former AusSAR SSARO in Australia, I am confused by the staggering amount of disinformation. A sudden or slight loss of pressurisation or fire on board as outlined above makes more sense to me.