RE Post 563
I wonder about the credibility of the Captain who was quoted as saying he had a conversation:
"He said those on the same frequency at the time would have heard the exchange.
This, he said, would include vessels on the waters below."
The Maritime Mobile Service uses frequencies in the range 150-160 MHz using Frequency Modulation, and well as some HF SSB. The aeronautical service uses frequencies between 108 and 132 MHz, using Amplitude Modulation, as well as some HF SSB.
The HF SSB frequencies are not in common between the services, unless we are talking about 2182 or 5680 kHz, the distress frequencies.
Two aircraft half an hour apart at 35,000 feet should be able to talk very clearly on VHF, where the boats below would not be listening (unless military). However I wonder why he would be using HF if VHF was adequate?
According to the article at New Strait Times link ;
....the captain, who asked to not be named, said his plane, which was bound for Narita, Japan, was far into Vietnamese airspace when
he was asked to relay, using his plane's emergency frequency, to MH370 for the latter to establish its position, as the authorities could not contact the aircraft.