(CNN) -- As the hunt for missing Malaysia Airlines Flight 370 now focuses on suspicious debris in the southern Indian Ocean, theories continue to evolve on what may have happened to the commercial plane carrying 239 people.
Conjecture by experts now ranges from the other-worldly to the generic.
It's been two weeks since the plane disappeared after a March 8 takeoff from Kuala Lumpur, heading to Beijing.
Theory: Ghost or zombie plane
The newest -- and most provocative -- speculation centers on the so-called "zombie theory" advanced most notably by aviation specialist Clive Irving of The Daily Beast.
Other experts, however, dislike his choice of words: "I really don't like the term 'zombie plane.' That connotes a sinister aspect to it. But, I'd prefer it to call it a ghost plane. But, we have seen things like this before," said William Waldock, a professor at U.S.-based Embry-Riddle Aeronautical University.
A ghost plane is one where everyone aboard -- pilots, crew, passengers -- loses consciousness because of a loss of pressurization, an explosion, smoke or fumes, experts say.
Under this supposition, the Malaysia plane experienced such an incident and, with everyone knocked out, continued to fly for hours on autopilot until the aircraft ran out of fuel.
It's not a fantasy. Such ghost-plane events occur, though rarely. For example, in 1999, a chartered Lear jet carrying professional golfer Payne Stewart and four others crashed in a South Dakota field after it flew on its own for four hours. That's because all aboard were dead after the cabin lost pressure -- with windows frosted over. Not even jet fighters shadowing the plane could stop it from running out of fuel and crashing.
"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. That's what we call a zombie option."
CNN aviation analyst Les Abend considers the thesis "very viable." Abend has flown the Boeing 777, the same kind of aircraft used for Flight 370.
"It can happen instantly if it's an explosive situation," Abend said. "It can happen insidiously if it's a slow situation. But my scenario is a smoldering fire that created smoke and once that smoke began the crew donned their oxygen masks. The unfortunate part is you can't totally see a lot of all that smoke from breathing and you're going to get some toxic fumes, depending upon what is burning."
Sensing a problem in the offing, 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.
"It sounds rather ominous to call it a zombie operation or a ghost ship, but in a way it is very ominous. As it progressed towards the waypoint, the toxic fumes perhaps overcame the crew and perhaps the passengers and at some point, they were no longer able to function," Abend said.
Other experts took exception, however.
"There's a lot of holes in that story. It's a very popular theory," said private pilot and aviation writer Jeff Wise.
If the pilot did turn the plane while under distress, then "you don't wind up southwest of Australia, you wind up in Africa," Wise said.
Miles O'Brien, another CNN aviation analyst and a former CNN correspondent, said he found the theory incredulous.
"To create this whole scenario where the plane is a zombie and they can't get a radio call off to say, 'We're in trouble here because we've got a fire burning,' I just find that a little bit hard to believe. They had good radio contact," O'Brien said. "You look at previous crashes where there have been fires or smoldering fires, and the crew is talking back and forth to air traffic control for quite a bit."
Theory: Incapacitated crew
The crew may have become incapacitated to fly the plane -- for whatever reason -- and unable to land the plane, said former pilot Alastair Rosenschein.
This theory focuses solely on the crew and assumes the plane may have crashed in the south Indian Ocean where sea and air searches are now taking place.
Under this concept, with the crew incapacitated none of the passengers would have the ability to take control of the plane or issue a distress call by radio. All or some may have been incapacitated -- or not -- as well.
"Let's be very clear about this: The aircraft would not have been in that location had the pilots had control of the aircraft,
had they been conscious and had they had the desire to save their lives and land somewhere," Rosenschein said. "So I would go on the premise that if the aircraft went down there, it was uncontrolled and ran out of fuel."
The location of the southern Indian Ocean would match the Boeing 777's maximum fuel range provide by investigators, said Robert Goyer, editor-in-chief of Flying magazine and a commercial jet-rated pilot.
"While there are a small number of possible scenarios at play here, the most likely, it seems to me, is that the airplane was flying on autopilot without anyone at the controls and did so until it ran out of fuel and crashed into the ocean," Goyer said in a CNN Opinion column. "The autopilot almost certainly would have remained working even after the plane ran out of fuel, though the dynamics of such a crash scenario are complex."
If the plane ran out of fuel while on autopilot, as in the ghost plane theory, 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 decent -- very similar, actually, to what you would experience in a regular flight, Casado said. "Just a very gradual decent but constant until you hit the ground."
If so, wreckage could be more easily recovered at sea, said aviation expert Ronald Carr.
"If it glides down and stuff, it's going to be less steep hitting the water, in which case it might stay more intact or it might be more pieces available to search for the debris pattern," Carr said. "If it comes down at a very steep angle like -- well, the one I'm thinking of is the Payne Stewart situation where the airplane was on auto pilot, ran out of fuel and then nosed over and came down pretty steep, and so there wasn't much aircraft left of that situation."
Experts haven't ruled out terrorism.
"You know there are some suggestion that it could (be terrorism), but that's a long way away from saying that there's any kind of evidence that it did," Flaying magazine editor Goyer said.
Malaysian military radar registered dramatic altitude changes for Flight 370 -- rising to 45,000 feet and then descending to 23,000 feet -- and an erratic path as it moved across Malaysia in what are some of the last known readings of the plane's location, according to a senior U.S. official.
The official, who is familiar with analysis of that radar data and declined to be identified because of the sensitive nature of the information, cautioned that this assessment is not definitive. The readings are not believed entirely accurate due to the distance the plane was operating from the radars that detected it, according to the official.
Still, analysts surmise possible causes for the altitude changes.
"Some of the flight profile changes might suggest that the flight was commandeered," Goyer said. "Was it by one of the pilot or by an intruder? It would be more likely that it was ... by one of the pilots. But, again, there's no evidence for that either way. The altitude changes that we saw could have suggested a struggle for the controls, if those reports are really accurate. And at this point, we don't really know how good that radar data is."
Theory: Pilot heroism or suicide? Or "barratry"?
Inevitably, public attention turns to the plane's captaining and whether the pilot and co-pilot deliberately tried to destroy the aircraft -- or save it from peril.
Among the disturbing circumstances of the plane's disappearance is how its transponder and communication systems were off shortly after takeoff.
Some experts postulate those systems failed because of fire, and the pilots pulled the main buses -- conductors carrying a computer system's data and control signals -- to "restore circuits one by one until you have isolated the bad one," pilot Chris Goodfellow said in Wired Magazine.
If the buses were pulled, "the plane would go silent. It probably was a serious event and the flight crew was occupied with controlling the plane and trying to fight the fire. Aviate, navigate, and lastly, communicate is the mantra in such situations," Goodfellow said.
He said radar reports that the plane ascended to 45,000 feet were unreliable. And, even if true, they are not necessarily damning. The pilot might have been seeking to quell the fire by going to an altitude with less oxygen, he said.
A reported rapid descent could have resulted from a stall at such a height, above the plane's limit, followed by a recovery at 25,000 feet. "The pilot may even have been diving to extinguish flames," he said. "But going to 45,000 feet in a hijack scenario doesn't make any good sense to me."
Other experts have advanced the possibility of the pilot -- or crew -- bent on annihilation of self and everyone aboard the plane.
For example, EgyptAir Flight 990 was flying 217 people from Los Angeles to New York to Cairo in 1999 when it crashed into the Atlantic Ocean. U.S. officials
blamed a co-pilot, who was recorded repeating a prayer, for deliberately causing the crash, but Egyptian officials blamed mechanical problems.
"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 and now works at the Washington consulting firm Spectrum Group.
Wise invoked a maritime legal term in describing possibly sinister acts by crew or pilots.
"I'm going to throw in a word here that hasn't been used very much and I think it's important to use it because are we calling it hijacking? Are we calling it sabotage? Are we calling it some kind of mutiny? The world in maritime law is barratry," Wise said. "Barratry is when the captain of a vessel commandeers it to sink it or to cause it harm. I think that's maybe what we're talking about here."
Theories: The bizarre
Unconstrained by the professional accountability under which the experts labor, some Internet users have ventured into the realms of the bizarre and paranormal -- which serve to show how the plane's disappearance captivates the world's imagination, for better or for worse.
Some assert a meteor struck the plane because one was reported in the area around the time Flight 370 took off. But given what little is known about the flight path, and the astronomical odds against such an event, a meteor strike seems like an ultra-long-shot explanation.
Some claim the plane landed on an airstrip without anyone noticing.
"What I have failed to read so far is the possibility that the pilot in command intentionally turned off the engines and performed a dead-stick landing at their intended destination," CNN.com reader Dave Mathews said in an e-mail. "Planes are essentially gliders with power and a 777 is no different, it is simply a big glider which makes zero noise with no power."
He cited the story of the so-called Gimli Glider, an Air Canada Boeing 767 whose captain glided it to safety at small Gimli airport when it ran out of fuel and lost power during a flight in 1983.
Lisa Williams, a psychic in California, said she believed the plane went down somewhere but with passengers still alive, though she doesn't have proof.
"Well, naturally, I don't actually have hard concrete evidence. And I think any psychic who has hard concrete evidence can't do their job correctly because they get misinformed," Williams said.
"I do believe that it actually crashed and I see a lot of trees. I didn`t specifically look into this for a reason, because I`m actually reading for some of the families' friends," Williams said on HLN.
"I kept feeling as though, yes, there are some people that have passed away because it's only natural after these amount of days someone is going to cross with no food, no water, but I also believe there was a hijacking," she said.
But CNN analyst Abend dismissed Williams' speculation as wild.
"With no 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."
CNN's Tom Watkins and Matt Smith contributed to this report.