The missing plane left behind a vapor trail of scenarios, and they have grown increasingly elaborate in the absence of information. The crucial evidence about what happened to Malaysia Airlines Flight MH370 on March 8 may be 2 1/2 miles deep in the Indian Ocean.
One awful possibility: We'll never know.
Aviation experts are discussing many possibilities, and they include:
1. Mechanical failure
The plane could have suffered some kind of electrical fire that caused a crisis and an emergency response. This was the hypothesis of a much-discussed article on Wired.com by a pilot who argued that the pilot must have turned the aircraft around in hopes of reaching an airport for an emergency landing, only to crash somewhere at sea.
Another possibility is catastrophic decompression. The crew could have lost consciousness and the plane could have kept flying — what people have been calling the "Payne Stewart scenario," after the golfer who died in 1999 when a Learjet underwent decompression and kept flying for 1,000 miles before crashing in South Dakota.
If the Malaysian plane's diversion was pre-programmed, as some reports suggest, that would pretty much rule out an accident. The pilot never radioed any distress, and the radios rely on batteries and would still operate after an electrical fire, said Hans Weber, an aviation consultant in San Diego.
Moreover, a fire would presumably be progressive and would allow time to transmit a distress signal. Sean Cassidy, an Alaska Airlines captain who currently is serving as national safety coordinator for the U.S. Air Line Pilots Association, said the lack of radio transmission makes the fire scenario difficult to believe. But the lack of communication doesn't prove anything, he said.
"Every single professional pilot is trained that, when you have an emergency, the first focus is on actually flying the plane, next is on navigating it, and the third priority is actually communicating," Cassidy said. "The absence of a distress call does not imply that there was no distress in the airplane."
Technically, a hijacking comes with demands, whereas commandeering can be for a variety of malevolent or idiosyncratic purposes. But in both cases this would have been a plane intentionally diverted on its flight from Kuala Lumpur to Beijing.
"It had enough fuel to go many places, and, unfortunately, it had enough fuel to go into places where you don't have civil radar systems, for example, and into a part of the world where terrorism and to some extent state-supported terrorism exists," said George Hamlin, an aviation consultant in Fairfax, Va.
He broached the possibility that this is part of an ongoing operation akin to the Sept. 11, 2011, attacks — including, perhaps, using the plane to deliver an explosive device somewhere. "It suggests something else horrific is being planned, because no one is claiming credit or saying, 'Ha ha, you have to deal with us.' "
Although this line of thinking has spawned a great deal of guessing, there is no hard evidence behind it. Investigators have not indicated that anyone on the plane has any affiliation with a terrorist organization or showed signs of a murderous mind-set.
Richard Aboulafia, an aviation analyst in Fairfax, Va., said he doubts Hamlin's scenario of the Boeing 777 being used to deliver a bomb. "Jeez Louise, why mess around with a triple-7? Go and rent yourself a Cessna," he said.
3. The plane landed
Hundreds of airfields were in range of the airliner. It's implausible that it landed at a major airport. This leads to speculation that it reached an abandoned airstrip.
"There's a lot of World War II airfields left over," said Ron Carr, a former pilot and a professor at Embry-Riddle Aeronautical University in Arizona. "These guys are not interested in protecting the airplane, so they're going to use minimal airfields. They're going to use one that's fairly secluded.''
There is no evidence that the plane landed, however. It would have had to elude radar coverage, land and then hide. This scenario also requires additional layers of speculation about the perpetrator and the motive.
4. Officials know where plane is
Officials in charge of the investigation may have decided to withhold information to protect investigatory assets (such as satellite capabilities), to cover up a mistake or national security inadequacy (such as a lack of good radar coverage), or to avoid tipping off people of interest.
"We're dealing with military organizations, and they don't want to tell you, and especially they don't want to tell you if it looks like they really screwed up," Weber said. "The military doesn't want to look bad in their own country. I think there is a lot of incentive for the militaries there to not come clean."
5. Terror attempt was aborted
If hijackers seized the plane, they conceivably could have been challenged by passengers or crew members, as happened on United Airlines Flight 93 on Sept. 11, 2001. Many scenarios emerge from this one. It's possible that hijackers intentionally crashed the plane in the Indian Ocean to cover the tracks of an ambitious operation that didn't quite work, but one that could be attempted again someday.
"That's the only thing that holds together with any logical consistency: that this is a failed 9/11," Aboulafia said.
Said Weber, "I think the most likely scenario is these terrorists managed to commandeer the airplane, and they set a route, and at some point the pilots fought with the people who commandeered the airplane and somehow everybody got incapacitated and there was no one anymore who could fly the airplane."