Carjockey:
I was under the impression that Viet Nam ATC alerted someone in Malaysia ATC. (around 0130-0140 or a bit after, when their attempt to contact the aircraft they expected went for naught) What happened within the various bits of Malaysian bodies who keep track of such things remains unclear. I am not sure that the assumptions you are making are correct, but your questions are well asked.
but something was obviously wrong because the aircraft transponder and comms were "off" or "disabled" for whatever reason.
What became obvious was that the flight was not on scheduled route. What seems to have become apparent was that attempts to contact and pick it up on secondary via squawk were unsuccessful.
The question must surely be why didn't ATC pick up on this and alert the civil and military authorities of neighboring countries immediately?
Good questions, but the answers aren't on this forum. They are within the various agencies in Malaysia.
Originally Posted by Leightman
I believe I have read all posts and do not recall any that address whether wreckage located next to a largely vertical and non-sedimented seafloor face (cliff) would reflect pings directionally, and if so might increase distances that a ping could be heard.
This is why I asked the question about bottom contour.
The terrain underwater can influence sound propagation.