- New theory from mathematician explains lack of debris
- Other experts say the crew may have become incapacitated
- If the pilot caused a crash, experts say it could have been suicide
(CNN)It has been 15 months since Malaysia Airlines Flight 370 from Kuala Lumpur to Beijing did an unexplained about-face, flew in the wrong direction and disappeared without a trace with 239 souls on board. In the absence of physical evidence, theories on what happened to the plane continue to proliferate: The crew passed out. It was pilot suicide. Or was it a paranormal event?
Now comes the latest contribution to the debate: This week, a mathematician from Texas A&M University announced that he had run data through a computer and determined it was likely the plane had plunged vertically into the ocean.
Goong Chen, using "applied mathematics, computational fluid dynamics and numerical simulations of a Boeing 777 in a classic 'water entry' problem," determined that a plane that piercing vertically into the sea would not break apart.
Simply put, a plane hitting the water at an angle would scatter its parts across the surface of the water. But one hitting at a near-vertical angle would shoot into the water with minimal damage and zoom straight to the bottom.
Never mind that the Indian Ocean is more than seven times the size of the United States -- a rather large area to search. The theory of the vertical dive, said Chen and his colleagues, explains why no debris has been found. The study was published in the April 2015 issue of Notices of the American Mathematical Society.
Chen offers no theories on why the plane might have been in a vertical descent. And he does offer a caveat.
"The true final moments of MH370 are likely to remain a mystery until someday when its black box is finally recovered and decoded," he writes.
But that has not stopped theories to sprout like weeds in an untended garden. Among those that have been circulated:
Theory: Ghost or zombie plane
Some speculation has centered on the so-called "zombie theory" advanced by aviation specialist Clive Irving of The Daily Beast.
A ghost plane is one where everyone aboard -- pilots, crew, passengers -- loses consciousness because of a loss of pressurization, an explosion, smoke or fumes.
Under this supposition, the Malaysia plane continued to fly for hours on autopilot until it ran out of fuel.
In 1999, a Lear jet carrying professional golfer Payne Stewart and four others crashed in South Dakota after flying on its own for four hours. All aboard had died when the cabin lost pressure.
"I think in the first few minutes of this emergency, the pilots had to change course because they were looking for an emergency airport," Irving said about the Malaysian flight. "They were at some point overtaken by whatever it was, smoke, fire, or some kind of problem. And the plane was then left to fly itself after it had been programmed to go on that course."
CNN aviation analyst Les Abend considers the thesis "very viable."
"It can happen insidiously if it's a slow situation," Abend said. "But my scenario is a smoldering fire that created smoke and once that smoke began the crew donned their oxygen masks."
The plane's captain may have "realized it was compelling enough to get the airplane turned and entered a waypoint that was an alternate airport in the flight management computer and kept the autopilot connected because this plane is designed, especially in an emergency situation to reduce workload," Abend said.
Theory: Incapacitated crew
The crew may have become incapacitated and unable to land the plane, said former pilot Alastair Rosenschein, causing the plane to crash in the south Indian Ocean, where numerous searches have taken place.
With the crew incapacitated, none of the passengers would have had the ability to control the plane or issue a distress call.
If the plane ran out of fuel while on autopilot, the landing at sea would have the same path as one on land, said Mitchell Casado, a Boeing 777 pilot trainer.
"It's not going to be any dramatic nose down or turning or anything like that. It's just going to be a very gentle, gradual descent -- very similar, actually, to what you would experience in a regular flight," Casado said. "Just a very gradual descent but constant until you hit the ground."
Malaysian military radar registered dramatic altitude changes for Flight 370 -- rising to 45,000 feet and then descending to 23,000 feet -- as it moved across Malaysia, according to a senior U.S. official.
The official cautioned that the readings are not believed entirely accurate. Still, analysts surmise causes for the altitude changes.
"Some of the flight profile changes might suggest that the flight was commandeered," said Robert Goyer, editor-in-chief of Flying magazine and a commercial jet-rated pilot. "Was it by one of the pilots or by an intruder? It would be more likely that it was ... by one of the pilots."
Theory: Pilot heroism or suicide?
Inevitably, attention turns to whether the pilot or co-pilot tried to destroy the aircraft. Those theories can only grow more insistent in the wake of the crash of a Germanwings plane in the French alps earlier this year, in which the co-pilot, Andreas Lubitz, is believed to have downed the plane deliberately in a mass murder-suicide.
Among the disturbing circumstances of MH370's disappearance is that its transponder and communication systems were off shortly after takeoff.
Some experts have advanced the possibility that the pilots or crew were bent on the annihilation of everyone aboard the plane.
"It's my belief that there was probably some type of struggle in the cockpit where it was one of the pilots that maybe had a meltdown or did something nefarious to the airplane," said Mark Weiss, a retired American Airlines pilot captain who has flown the Boeing 777.
Theories: The bizarre
Some Internet users have ventured into the bizarre and paranormal.
Some assert a meteor struck the plane. But the astronomical odds against such an event are high, to put it mildly.
Lisa Williams, a psychic in California, said she believed the plane went down somewhere with its passengers still alive, though she doesn't have proof.
"I do believe that it actually crashed and I see a lot of trees . . . " Williams said. "I also believe there was a hijacking."
But Abend, the aviation analyst, dismissed Williams' speculation.
"With(out) disparaging Lisa's profession, I mean, listen, I'm an airline pilot. I deal in black and white," Abend said. "It's difficult for me to, in this particular circumstance, to think that a psychic could solve a problem that people all over the world are not able to solve at this point."