The current theory apparently being promoted by officials is that the crash of the Malaysian plane may have been an act of suicide, most probably by a pilot.
But do mental health experts agree that this is the most likely explanation of this deepening mystery?
Professor Robert Bor is a Clinical and Specialist Aviation psychologist, co-editing with Todd Hubbard, the key book on the subject of pilot mental health: entitled 'Aviation Mental Health'. It is published by Ashgate.
The book considers the psychological assessment, management, treatment and care of pilots as well as other professional groups within aviation.
Professor Bor, in response to the latest theory of pilot suicide in the case of the Malaysian Airlines Jet, is careful not to rule out the suicide possibility, but cautions that this is incredibly rare. When it happens, it is much more commonly in private pilots, who are not licensed to carry passengers.
But Professor Bor concedes that incidents involving commercial pilots are not unknown, and he points to the example of an Air Botswana pilot, who in 1999 crashed his plane into other aircraft on the ground of an airport in an apparent suicide mission.
The act appeared to be by a disgruntled employee, angry with the airline and his employers, wanting to take revenge. This suggests that if a commercial pilot kills themselves in this way, grievance towards the airline could be a key motivation.
This is probably being covertly investigated right now in the Malaysian Airlines case.
The Air Botswana pilot flew a commercial plane without permission and without passengers. He may have been angry and despairing that he had been grounded due to ill health. He may have thought he was never going to fly again. During negotiations with the tower, as he flew around the airport, he was said to have threatened to fly into the Air Botswana Office Building.
Within 24 hours of the Air Malaysian Flight going missing, Professor Bor explains that inquiries into the backgrounds of the two pilots would have been initiated, to investigate a similar suicide motive.
He elaborates that investigations into the pilots' mental health profiles would review spending patterns, possible relationship difficulties, drug use and any other behavioural disturbances.
But the Air Botswana incident involved a key life event, being grounded and discovery of a career-threatening health problem, none of which appears to have yet emerged in the Malaysian scenario. This reduces the possible likelihood of suicide, in Professor Bor's opinion. However, he concedes anything, at this stage, is possible.
Another problem with the suicide theory is that, in the Air Botswana case, as reported by sources quoted by Reuters news agency, the pilot threatened suicide not just during the flight itself: he had repeatedly warned authorities that he was going to kill himself.
Professor Bor points out, 'no one wakes up one morning and suddenly decides to kill themselves', usually the intent emerges over a longer time. Yet given pilots are probably the most scrutinised profession on earth, it seems unlikely that even minor aberrations would have gone undetected before.
Commercial pilots don't just have frequent medical checks, they are being closely observed by colleagues on the flight deck as well as by other professionals, during, before and after flights. (Some planes haven't been allowed to leave the ground because the dispatcher smelt alcohol on the breath of a pilot.)
Professor Bor points to another case which may provide clues as to what happened.
In 1994, a Federal Express cargo Flight flying across the USA became the victim of an attempted hi-jacking by an employee facing dismissal. He boarded as a passenger with a case hiding several hammers. He intended to disable the aircraft's systems so that events were not properly recorded and, once airborne, to kill the crew using the hammers so injuries would appear caused by the crash. The plan was then to collide the aircraft, so the perpetrator would appear just another employee killed in an accident. His family would become eligible for a $2.5 million Federal Express life insurance policy.
But despite severe injuries, the crew fought back, restrained the perpetrator and landed the plane safely.
Dr Jennifer Morse, a consultant in Aerospace Psychiatry and Assistant Clinical Professor of Psychiatry at University of California San Diego Medical School, co-authored with Professor Robert Bor the chapter on the mental health of pilots in the book 'Aviation Mental Health'.
In their joint chapter they draw attention to Egypt Air Flight 990 which crashed in 1990, and where the relief first officer was recorded as saying 'I rely on God' just before disengaging the autopilot. He then went on to make the statement 11 times during the plane's impending crash, without any apparent emotion. While suicide seems the most likely cause, the precise motive remains mysterious.
Morse and Bor report an estimate between 0.72% and 2.4% of general aviation accidents are as a result of pilot suicide, and a history of psychiatric or domestic problems have been found in such post-crash inquiries and investigations.
Morse and Bor point out that one possible reason why a commercial suicidal pilot might choose to crash their plane, is that the evidence it was a suicide might be thus destroyed, so protecting their family, and the memory of the pilot, from the 'shame' of suicide.
Using the plane as the instrument of death might also be psychologically entwined with resentment against the stress of the job, or grudges against the airline employer.
But Professor Bor also points out that psychology is crucially involved in the search for the plane and investigation of the cause, given the danger of a psychological phenomenon termed 'confirmation bias'.
Confirmation Bias occurs when you've already made your mind up and this biases the way you approach the evidence. The search for this plane may have been fatally hampered by a series of 'confirmation biases'.
It's vital, Professor Bor argues, that crash investigators remain open-minded and don't start looking merely for confirmation of a prior held theory.