The disappearance of Malaysia Airlines Flight 370 sparks more questions than answers as 26 countries search for the plane more than a week and a half after its last signal faded away.
The mystery of what happened to the plane and the 239 people aboard deepens each day when partial explanations that emerge unravel.
If there was a catastrophe – a crash or a breakup in flight – where is the wreckage?
If somebody commandeered the flight, either the plane landed safely or there was a crash. But where, in a circle of possibilities more than twice the width of the United States, are the answers?
"First off, they've got to find the darn thing," said William Waldock, who teaches aviation safety at Embry-Riddle Aeronautical University in Arizona.
A look at the leading theories to what happened to Malaysian Airlines Flight 370:
The mystery began about 40 minutes into a five-hour flight from Kuala Lumpur to Beijing, about the time the drinks service might begin on a flight from New York to Los Angeles.
The Boeing 777-200ER took off at 12:41 a.m. on March 8. At 1:07 a.m., the plane's automated maintenance system stopped communicating with its airline. At 1:21 a.m., its transponder stopped signaling its location to air-traffic controllers and other planes.
In the final radio contact from the plane, a pilot said, "All right, good night." Airline CEO Ahmad Jauhari Yahya said the comment apparently came from co-pilot Fariq Abdul Hamid.
The timing of the comment has been disputed, and if it came after the equipment stopped transmitting, it could mean the pilot was involved in whatever happened. But Yahya said Monday that it came before the communications equipment stopped.
The abrupt disappearance initially suggested to ground controllers and aviation experts that the plane met a catastrophic end, either breaking up in flight or simply crashing into the Gulf of Thailand.
An electrical fire, or perhaps a fire from hazardous cargo, could have knocked out communications equipment. The disaster would have had to happen quickly enough to prevent crewmembers and passengers from calling for help.
Swissair Flight 111 crashed into the water off Nova Scotia in 1999 after a fire forced pilots to try an emergency landing, according to Canada's Transportation Safety Board. The fire knocked out communications and the flight recorders five minutes before the plane hit the water, although the pilots were able to call for help before that.
Canadian pilot Chris Goodfellow cited the Swissair case in proposing in wired.com that the Malaysia pilot could have noticed a fire, turned the plane toward an emergency runway and then lost control of the plane as it continued to fly.
ABC News reported that an oil-rig worker in the Gulf of Thailand said he saw the Malaysia plane "burning at high altitude," but later said the report could be a hoax.
If the plane depressurized and killed its occupants, like golfer Payne Stewart's business jet in 1999, that would explain the silence from crew and passengers. But aviation experts say in that case, the plane should have kept flying automatically toward Beijing and should have been noticed along the path.
In two troubling earlier incidents – a SilkAir crash in 1997 and an EgyptAir crash in 1999 – investigators determined that pilots intentionally steered their planes into the water after persuading colleagues to leave the cockpit.
But those incidents happened relatively quickly after the planes took off. In the Malaysia flight, later clues suggested the plane flew more than seven hours.
Ships and planes from 10 countries searched the Gulf of Thailand for days in relation to the final radar contact but failed to find any signs of wreckage.
As investigators studied the chronology, they suspected the different times that the equipment stopped sending messages meant somebody turned it off intentionally. This would require somebody familiar with the plane's equipment – the pilot or co-pilot, or perhaps somebody else on board.
The passenger manifest included two Iranian men – Pouria Nour Mohammad Mehrdad, 19, and Delavar Seyed Mohammadreza, 29 – who were traveling on stolen passports, which would have raised flags in the U.S.
But Interpol and Malaysian officials said the men were simply seeking to emigrate to Europe.
The FBI is also checking on the two pilots' background and their homes have been searched.
Capt. Zaharie Ahmad Shah was a member of Malaysia's opposition party and he attended a hearing before the flight where an opposition leader was jailed.
The co-pilot, Hamid, was photographed allowing two teenagers in the cockpit with the crew during a December 2011 flight. Malaysia Airlines officials said they were "shocked" by the allegations.
But the FBI hasn't released any information suggesting either pilot was bent on intentionally crashing the plane or commandeering it.
THE TRAIL RESUMES
At 2:15 a.m., Malaysian military defense radar picked up traces of the plane hundreds of miles west – heading in the wrong direction – from its last signal. This revelation days after the plane disappeared led to confusion about whether the search should be focused in the Gulf of Thailand or west to the Indian Ocean.
The plane crossed the country's peninsula and headed into the Strait of Malacca in a zig-zag path along typical flight routes, in what Prime Minister Najib Razak said was "consistent with deliberate action by someone on the plane."
The plane's guidance system was programmed for the new route either before or during the flight, which would have required familiarity with the equipment, The New York Times reported Tuesday.
This radar tracking is what prompted the search to widen from east of the narrow peninsula to west, and up to the Bay of Bengal. But again, no wreckage was found by search planes or ships.
Gaps in radar coverage demonstrated throughout the ordeal raised the prospect the plane could have landed – or crashed – on the ground.
Likewise, the plane's height could have prevented crewmembers or passengers from using cellphones to warn about the plane's diversion – if they'd noticed.
But ground searches could be difficult, too. Nearly 70 years after the end of World War II, searches continue for an estimated 100 British and American war planes hidden in remote jungles across Malaysia, Thailand and India.
An aviation enthusiast, Keith Ledgerwood, posted a theory on tumblr.com that gained widespread attention that Flight 370 remained unnoticed as it flew across Malaysia by trailing a Singapore Airlines flight along the same route at nearly the same time. Both planes would travel under the same radar blip.
A simpler explanation could be that the radar track mistakenly thought to be Flight 370 is really the Singapore flight.
This guesswork about a hidden Flight 370 is intriguing, though, because it would allow whoever was in control of the missing plane to follow the Singapore flight toward Spain before veering off over India or Afghanistan to land unnoticed somewhere.
But a cargo plane from a less developed country would have been easier to steal. For the Malaysia flight, this theory would again require a knowledgeable pilot to reprogram the plane, follow a sophisticated route, keep the rest of the crew and passengers silent and either land or crash somewhere.
"I seriously doubt it," said Patrick Smith, a commercial pilot who blogs at the site askthepilot.com. "Remote as some airports are, none are small or unwatched enough to accept a Boeing 777 without it being obvious."
Despite the lack of messages from the plane's maintenance system, it continued to search for a satellite with an electronic "ping," in case it needed to send a potential message, as first reported by The Wall Street Journal.
This reinforced the notion that somebody intentionally turned off the equipment, rather than having it destroyed by in-flight fire or a crash.
At 8:11 a.m., the final ping sounded seven and a half hours after the plane took off.
An Inmarsat satellite orbiting 22 miles above the Indian Ocean was only able to detect how far away the signal was, not its precise location. That led to the current search in two major arcs stretching over multiple countries and thousands of miles of ocean.
The arcs themselves are imprecise because the plane conceivably could have kept flying an hour after the final ping before its fuel ran out.
The arc to the north is over land, stretching from Laos across China to Kazakhstan. Civilian or military radar might have picked up the plane along that route, but no sightings have been released publicly.
The arc to the south stretches from Indonesia across the Indian Ocean. This space is daunting because there is little radar coverage from Australia, which is helping search from the east, and the water is deep.
Given the length of flying time, the potential search area is now a circle 6,400 miles in diameter around where the plane took off.
The WNYC Data News team found 634 runways in 26 countries within that circle where a 777 could have landed.
After so many days of uncertainty, relatives of the passengers are eager to learn their fate. "The fact that there was no distress signal, no ransom notes, no parties claiming responsibility, there is always hope," Malaysian Defense Minister Hishammuddin said at a news conference.
If the plane did come down over water, the search is urgent for possible survivors or wreckage. The amount of debris will depend on how the plane hit the water.
When Air France Flight 447 crashed in the Atlantic Ocean, searchers found floating wreckage in five days and pulled material from the surface for 25 days. But even then it took nearly two years to find the plane's recording devices and rest of the wreck on the ocean floor to determine what went wrong.