With no distress signal, no sign of any wreckage and no credible claim from terror groups, investigators on Tuesday began to consider whether the pilots or passengers may be to blame for the disappearance of Malaysia Airlines flight MH370.
"We are looking into four areas: one is hijacking; two, sabotage;three, psychological problem of the passengers and crew; and four, personal problem among passengers and crew,” Malaysian police chief Khalid Abu Bakar told reporters in Kuala Lumpur Tuesday.
But in a post-9/11 world, it is hard to imagine what type of human activity could bring down a modern jet so quickly that not a single alarm was sounded.
For instance, when a JetBlue captain had a mid-air mental breakdown on his New York-to-Las Vegas flight in April, he was locked out of the cockpit by his co-pilot and subdued by passengers until the flight made a safe landing in Texas.
Could a similar disturbance explain what happened to the Malaysia Airlines Boeing 777?
"Maybe somebody on the flight has bought a huge sum of insurance, who wants family to gain from it or somebody who has owed somebody so much money, you know, we are looking at all possibilities," Bakar said. "We are looking very closely at the video footage taken at the [airport and] we are studying the behavioral pattern of all the passengers."
With those remarks, eyes are turning toward the 1997 Silk Air crash in which a Boeing 737 plunged so rapidly into an Indonesian river that only six of 104 victims were positively identified.
U.S. officials who helped the international investigation concluded that the evidence was consistent with a deliberate manipulation of the controls — most likely by the Singaporean captain, who had reportedly incurred debts of more than $1 million and was already facing disciplinary action.
The cockpit voice recorder had been intentionally disconnected, but a possible rudder failure meant pilot suicide could not be conclusively proven as the cause.
Only two years later, EgyptAir Flight 990 plunged into the sea off Massachusetts, killing all 217 on board. Cockpit voice recordings revealed that one of the relief co-pilots, Gamal al-Batouti, repeated the Arabic phrase “I rely on God” several times before the plane entered a rapid, deadly dive.
The United States' National Transportation Safety Board concluded that al-Batouti’s action at the controls had probably caused the Boeing 767 to crash, but again the motive for that action was “not determined” and Egyptian officials rejected the suicide theory.
Health checks for pilots
Malaysian commercial pilots undergo health checks at similar time intervals to those in the U.S., but it was not immediately clear if those tests match American requirements for mental competence.
Federal Aviation Administration rules require captains to have a first-class medical certificate, renewed every year if the pilot is under 40 and every six months if 40 or over. First officers (co-pilots) need a second-class certificate - renewed every year - but some airlines insist all pilots must have first-class certificate.
Applicants must have an established medical history clear of any “personality disorder” or problems such as “delusions, hallucinations, grossly bizarre or disorganized behavior.”
Pilots must also declare any neurological conditions or incidents such as drunk-driving convictions, and their psychological fitness is assessed by an FAA-approved physician.
But there are loopholes.
“The system relies on pilots self-declaring, so unless a pilot is honest about an alcohol problem or a psychiatric disorder, there’s no guarantee a problem would be spotted,” said Diane Damos, who holds a doctorate in aviation psychology and whose company specializes in pilot selection and screening.
“The tests are also strictly on the medical side. Issues such as aptitude and suitability are largely left up to the airlines to figure out.”
Such gaps might explain the bizarre incident in February in which one of the pilots of an Ethiopian Airlines jet from Addis Ababa to Italy locked his co-worker out of the flight deck during a bathroom break and hijacked the plane, diverting it to Geneva, Switzerland, before demanding political asylum. He now faces criminal charges and up to 20 years in jail.
David Gleave, a British air safety expert who worked on the Silk Air crash, said it was possible that the emergency beacons of the Malaysian jet might also have been turned off deliberately.
“It seems to have disappeared at exactly the point of maximum confusion,” he said. “It has gone missing between the Malaysian air traffic control area and the area controlled by Vietnam. There is no signal at all from the data recorder, and it has seemingly changed course without being detected. Who would know how to do all that? Somebody who knows what they are doing.”
Could an unstable passenger bring down a flight? Air rage is a known problem, and last month a serial arsonist was suspected of repeatedly setting fires aboard a Boeing 777 heading from Australia to the Middle East. A number of passengers were questioned but no culprit was identified.
Could the plane have been hijacked?
Hijacking an airliner is a formidable task thanks to post-9/11 rules that require cockpit doors to be reinforced and locked throughout the flight, except when pilots visit the bathroom.
A coded distress signal is easily activated by pilots if anyone tries to enter the cockpit –- a system that proved effective when a drunk passenger tried to hijack a Turkish jet at the start of the Sochi Winter Olympics last month.
“Cabin crew are supposed to block anyone from getting close to the cockpit area while the door is open,” said Damos. “Nobody should by anywhere near the flight deck.”
That’s why Malaysia Airlines said on Tuesday that it was “shocked” by a report that the first officer on the missing Boeing 777 broken the airline’s rules by allowing passengers to sit in the cockpit during take-off and landing.
Jonty Roos, from Australia, said that she and a friend were on vacation in 2011 when they were invited to the flight deck by two pilots – one of whom she identified as Fariq bin Ab Hamid, the 27-year-old co-pilot of Flight MH370. She said the pair also smoked during the flight.
A pilot willing to bend the rules might leave the plane exposed to a hostile passenger, said Damos. “If the report is true, that is a huge security breach. It would absolutely get you fired in the U.S., and likely the airline would be investigated, too. Are Malaysia Airlines pilots in the habit of letting passengers into the cockpit?
"It would only take a short dash through first class to get to an open door. It also begs the question of what the cabin crew was doing at the time. They should have reported the incident.”
Damos added that observing the security video of passengers prior to boarding might yield some clues. "The Israelis, for example, look very closely at how passengers behave as they pass through security and during boarding. They don't say what signs they are looking for, for obvious reasons."
Measured against the thousands of commercial flights that take off around the world each day, instances of hijack or suicide-by-pilot remain rare, and some experts say investigators should focus on more conventional explanations such as mechanical failure.
"I think it's an unfortunate red herring,” said Clive Irving, author of “Wide-Body: The Triumph of the 747” and aviation correspondent for the Daily Beast. “There is no evidence so far pointing to a struggle in the cockpit. Whatever happened seems to have been instantaneous.”
He said that the Malaysian investigators appeared to be “inexperienced,” adding: “I think the truth is that they are just as mystified as we all are.”