Five days ago, Malaysia Airlines Flight 370 vanished into thin air. With no distress calls and no warning signs, a Boeing 777 aircraft carrying 227 passengers simply disappeared. Just 40 minutes after the plane departed Kuala Lumpur for Beijing with members of 14 different countries on board, it abruptly vanished from radar screens. And as of today, a massive search consisting of over 40 ships, 34 aircraft, and 10 orbiting Chinese defense satellites have yet to find any trace of the plane.

If Flight 370 had broken apart or exploded in midair, there should be some debris, but none has been found so far. An oil slick which could have come from a crash didn’t contain any jet fuel, while a supposed life raft turned out to be a moss-covered top of a box. "We have not found anything that appear to be objects from the aircraft, let alone the aircraft," Malaysian authorities said Monday, telling families to prepare for the worst.

But how can an airplane simply disappear? Apparently, it’s not impossible. According to aviation experts interviewed by Wired, pilots are supposed to react to emergencies before they phone home. They also aren’t necessarily in constant communication during the trip. Over the ocean, civil aviation systems might not have been able to track the plane further than 100 miles from shore. The mystery isn’t just why Flight 370 disappeared, it’s what could possibly have happened to keep it from reappearing once more.

Authorities aren’t willing to rule out terrorism, but it’s looking like the least likely of the theories so far. Early on, rumor had it that the airline loaded luggage from passengers who didn’t board the plane, implying a possible bomb. However, Malaysian Airlines soon refuted the luggage claim: though four passengers booked the flight without boarding, they also didn’t bother checking in at the terminal. And though two Iranians boarded the flight with stolen passports, raising fears of terrorism, it appears they may have simply been trying to illegally immigrate to Germany. "We haven’t ruled it out, but the weight of evidence we’re getting swings against the idea that these men are or were involved in terrorism," a Thai police chief told Reuters. There’s also no debris, no terrorist groups taking responsibility for an attack, and no attempt to use the plane as a weapon.

A relatively young Boeing 777

Mechanical failure and pilot error are thought to be the most likely causes of an accident, and many are already drawing comparisons to the deadly crash of Air France Flight 447 in 2009. That plane dove into the Atlantic Ocean, killing 216 passengers. Reportedly after the pitot tubes (which measure airspeed) froze it caused the autopilot to fail, and the crew failed to recover from a disastrous stall as it attempted to navigate turbulent weather conditions. The Air France crew, too, failed to radio for help. Others have pointed out that aging aircraft can break apart in flight if improperly maintained.

But Flight 370 took place on a relatively young Boeing 777, an aircraft with a reputation for safety, and this particular plane saw maintenance less than two weeks before the incident. The aircraft also disappeared in good weather, on an easy leg of the journey, and with an extremely experienced captain who allegedly knew the plane like the back of his hand. There’s already an online tribute dedicated to 53-year-old Captain Zaharie Ahmad Shah, a man with 18,000 hours of flying experience and an instructor who trained younger pilots on the Boeing 777 in particular. He even built his own Boeing 777 flight simulator to use at home, and developed a reputation as a master of the plane. "He knew everything about the Boeing 777. Something significant would have had to happen for Zaharie and the plane to go missing. It would have to be total electrical failure," one of his colleagues told Reuters.

It does seem, however, that his co-pilot might have been prone to distractions. An Australian woman recently came forward to claim that 27-year-old Fariq Abdul Hamid invited her and a friend to sit in the cockpit during their entire flight in 2011, while smoking and flirting with the young women. Still, the woman, Jonti Roos, says she felt the pilots seemed competent at their duties.

The flight's co-pilot may have been prone to distractions

Besides, new evidence may be pointing a different direction: to suicide or hijacking. Though civil air traffic systems lost the plane 40 minutes after takeoff, Malaysian military authorities told Reuters and the local Berita Harian newspaper that they spotted the aircraft far west of its intended route — in the Strait of Malacca, west of Malaysia itself. If true, that means that the plane would have actually had to cross the peninsula, leaving its transponder off to avoid detection by air traffic control, and fly at least 350 miles after its original disappearance without a major mechanical failure. That suggests that a pilot was in control of the aircraft and had plenty of time to radio home about a change of route.

On rare occasion, aircraft can also stray far off course when the pilots are incapacitated by hypoxia, a lack of oxygen that occurs when the cabin isn’t properly pressurized at altitude. This is the fate that befell Helios Airways Flight 522, a Cypriot 737 that circled Athens on autopilot after the captain and first officer failed to correctly set the pressurization system. An unpressurized cabin also led to the death of noted golfer Payne Stewart after the Learjet he was on ran out of fuel and crashed in a field in 1999, having traveled some 1,500 miles off its intended flight path.

But strangely, Malaysia is now denying ever seeing the plane over the Strait of Malacca. Air Force chief Rodzali Daud denies making such a statement to the local paper, and a spokesman for the country’s prime minister relayed that senior military officials had no evidence that the plane ever recrossed the peninsula.

Actions may speak louder than words, though, as the search operation had already expanded to the out-of-the-way Strait of Malacca without any such explanation, and it seems authorities are actively investigating those possibilities. In a recent press conference, Malaysia’s inspector general said investigators would specifically look into whether this could be hijacking or sabotage, or whether there were personal or psychological problems among the crew or passengers that could have led to a suicide attempt.

For now, we simply don’t know the truth of what happened on board Malaysian Airlines Flight 370. Authorities say that until the investigation is complete, they aren’t ruling out any possibilities.

Update 3/13: The Wall Street Journal has sources claiming that Flight 370 flew for a total of five hours based upon data automatically sent from the 777's satellite-communication link.

While Malaysia's acting transport minister has reportedly stated that such claims are inaccurate, ABC News reports that the Pentagon too believes that the plane may have flown for an additional four or five hours after disappearing. Officials are reportedly now say that there is an "indication" that the plane crashed in the Indian Ocean, and a ship is being sent to investigate — though it won't arrive until Friday.

Malaysia's defense minister also said that Chinese satellite imagery, previously noted above, did not show debris from the aircraft. Authorities had been investigating three large objects in the imagery, which some suspected may have been parts of the wreckage. "We have contacted the Chinese Embassy who notified us this afternoon the images were released by mistake and did not show any debris from MH370," ABC News reports the defense minister saying.