What Happened to Malaysia Airlines Flight 370? Terrorism Ruled Unlikely, So Here Are 4 Possibilities

After days of searching and investigating, it remains completely unclear what happened to Malaysia Airlines Flight 370, and officials don't appear to have any concrete leads. The jetliner carrying 239 people disappeared Saturday on its way from Kuala Lumpur to Beijing.

Though the possibility of a terrorist attack hasn't been ruled out, it's looking less likely than ever. On Tuesday, police said the two passengers who travelled onboard with stolen passports were Iranian nationals, one possibly seeking asylum. "The more information we get, the more we are inclined to conclude it is not a terrorist incident," Interpol's Secretary General Ronald Noble told Reuters.

And on Monday, officials discovered their only real lead— oil slicks seen in the South China Sea — weren't from the missing Malaysia flight. So with that possibility scratched off the list and the ever-decreasing likelihood of a terrorist plot, what might have happened to Flight 370? Here are four possibilities...

Mechanical Issues

Search-and-rescue teams from more than eight countries have been scanning the seas for debris or hints of what might have happened. No signs of any wreckage have been discovered.

Though mechanical failure is possible, it doesn't quite hold water, since pilots would almost certainly have had time to radio back and report issues with the aircraft. Malaysian military officials say the plane may have turned around mid-flight, indicating there could have been issues with the Boeing 777: The crew could have suspected something went wrong and attempted to return.

The missing plane did have a registered clipped wing a couple of years back, but it was repaired and deemed safe to fly.

Midair Explosion

A midair disintegration could explain why no debris has been found in seas under the plane's flight path, and why the plane crew didn't have time to register a distress signal. One source involved in the investigations told Reuters the lack of evidence may "indicate that the aircraft is likely to have disintegrated at around 35,000 feet."

However, Malaysia Airlines has one of the best safety records in Asia, with its last fatal accident in 1995, almost 20 years ago. And the Boeing 777 model, made in the U.S., has proven to be one of the most reliable aircrafts on the market.

Extreme Weather

A bad storm could have, theoretically, brought down the Boeing — but the aircraft was built to withstand harsh environments, and the forecast for the flight was clear skies.

Still, there's precedent for a plane disappearing mid-storm. in 2009, an Air France plane crashed into the South Atlantic after a heavy thunderstorm. Debris was spotted a day after the reported incident, but the aircraft's fuselage remains to be found, and "black box" flight recorders weren't recovered until two years later.

Pilot Error

Flight data suggests that the Boeing 777 experienced a very rapid loss of height and change in direction. Suicide or international sabotaging by the flight's pilot could be to blame, and would also explain why there was no contact.

Flight 370 may have also experienced pilot disorientation, with the pilot taking the plane off autopilot and veering off course. Another possibility is crew malfeasance, meaning crew members could have been trying to address a problem onboard, but were so preoccupied they didn't realize the seriousness of the problem in time.