On March 8, 2014, Malaysia Airlines flight 370 (MH370) lost contact with air traffic control on its way from Kuala Lumpur International Airport in Malaysia to Beijing Capital International Airport in China. The plane was never found. Now, it’s been four years since MH370 vanished, and we still don’t have all of the answers. Here’s what we know — and don’t know — happened, and why experts still aren’t sure of the real cause.

The cause of the disappearance is still unknown

MH370 has been called one of the strangest aviation mysteries of all time. The plane departed Malaysia at 12:41 a.m. local time and was set to arrive in Beijing about six hours later. It never arrived at its final destination, but according to satellite radar, the plane was in the air for at least seven hours — much longer than its anticipated flight time. The length of time that the flight was in the air makes drawing a conclusion about its disappearance that much more complex. Four years later, all passengers are “presumed” dead, but no significant evidence has been found to confirm what happened.

Next: This is one of the biggest unknowns about the plane.

The site of the presumed crash still has not been pinpointed

When MH370 dropped off of satellite radar, it left air traffic controllers unsure of exactly where the plane went down. It was confirmed that the plane was headed in the opposite direction of its planned route, but there was no official word on where it crashed. After the incident, search and rescue teams searched nearly three million square miles’ worth of ocean to no avail. Plenty of satellite, aviation, and military radar controls picked up the plane throughout its course, but none know exactly where it ended up.

Next: Experts ruled out terrorism.

Experts investigated every one of the passengers

After the disappearance, experts looked in to every single passenger to find out if anyone could have been responsible for a terror attack. The only questionable thing the background checks uncovered were that two Iranian men were traveling on stolen passports. However, it was soon realized that they were seeking asylum and were not listed as suspects. All other checks showed nothing that pointed toward a passenger terrorist attack.

Next: Takeoff was nothing out of the ordinary.

There were no problems with takeoff

The flight was cleared for takeoff and departed at 12:41 a.m. According to communications with air traffic control, the flight easily climbed to 18,000 feet, then was cleared once again to reach 35,000 feet. Voice analysis confirmed that the pilot definitely spoke with controllers on the ground after takeoff. The flight confirmed it had reached its cruising altitude at 1:01 a.m. and reinforced it again at 1:08 a.m. (Some experts believe the re-confirmation of the plane’s altitude just minutes later is suspicious.)

Next: Things got shaky less than an hour into the flight.

The last communication with the cockpit was 54 minutes into the flight

MH370 took off without a hitch. The pilots were in communication with the ground up until Kuala Lumpur instructed them to start communication with Ho Chi Minh (as aircrafts travel into different airspaces, they switch whom they communicate with). When communication switched, the pilots were not heard from again. A distress signal was never sent from the aircraft at any time during the flight.

Next: A pilot of another plane claims he got in touch with MH370.

When MH370 pilots stopped responding, another plane was able to get in touch with it

After failed attempts from air traffic controllers, a nearby plane on its way to Japan was asked to reach out to MH370, since it was flying only 30 minutes away. The captain of that plane said he was able to make contact with the flight but could only hear static and mumbling.

Next: Military radar spotted something concerning.

Military radar saw the plane make unnecessary turns and veer off course

Just as MH370 entered into Vietnamese airspace, it veered off course. Military radar saw the plane turn right, but then it made a sharp left turn and headed southwest. Various theories have surfaced about why the plane might have taken such a sharp turn backward. Some believe the plane intentionally waited until it crossed airspaces before making the turn, hoping that there would be some “dead” air space where its turn would not be immediately detected.

Next: The plane’s location eventually became unknown.

The plane’s last known location was at 2:22 a.m. — about 1 hour and 40 minutes into the flight

The military confirmed the flight’s location at 2:15 a.m. Radar showed the plane traveling south of Phuket Island in the Strait of Malacca, completely off course from Beijing. Initially, the government thought the last known location was at 2:15 a.m., but further investigation showed otherwise.

Next: The plane remained in the air for hours after it veered off course.

Data showed the plane in the air all the way through 8 a.m.

Although the plane’s last known location was 2:22 a.m., a satellite orbiting above the Indian Ocean picked up the plane on its radar long after that. According to BBC, the satellite showed the plane still off course at 8:11 a.m. and again at 8:19 a.m., close to eight hours after its initial departure from Kuala Lumpur.

The involuntary communication with the satellite was referred to as a “handshake” and it meant the plane’s electrical system was trying to log back on. This is consistent with an electrical problem or power outage occurring on the plane.

Next: People claim to have seen the plane go down.

There were several reported sightings of a plane going down in the Indian Ocean

In the days after the disappearance, several people came forward saying they thought they’d seen a plane go down in the Indian Ocean. One group of fishermen said they believed they’d seen a plane flying surprisingly low around 1:30 a.m. — the same time MH370 lost contact with the ground. One woman who had been sailing across the Indian Ocean with her husband claimed she’d seen MH370 on fire in the sky.

Next: The washed-up debris has provided very few answers.

In 2015, the first piece of debris washed up on a small island

In July 2015, a piece of an airplane wing washed up on Réunion Island, a small island east of Madagascar. Experts confirmed that the serial number of the flaperon proved to be from a Boeing 777. MH370 was the only missing Boeing 777, and it was concluded that the fragment was part of the vanished plane. Since then, several pieces of debris have washed up along the African coast. Pieces have been found as far north as Tanzania and as far south as South Africa.

Next: Conspiracy theories continue to develop.

Since then, conspiracy theories have been all over

There have been dozens of reported conspiracy theories about the plane since no true conclusions have been drawn. Some people think rapper Pitbull had something to do with the crash after he “predicted” a Malaysia airlines crash in one of his songs. Others believe it was aliens, and some think the Unites States military was involved. But some more credible theories suggest hypoxia, meaning everyone on board suffocated when a pressure issue occurred on the plane. The plane may have remained on autopilot until it ran out of fuel.

Next: January 2018 marked a new investigation.

A new investigation was launched in January 2018

At the beginning of 2018, private U.S. firm Ocean Infinity agreed to continue the search for the missing plane. Malaysia agreed to pay Ocean Infinity up to $70 million if the plane was found within 90 days, not including time needed to refuel. As of the beginning of March 2018, the firm had not made any significant findings, but the search was expanded through June 2018.

Next: An unexplained disappearance created controversy in the 2018 search.

In late January 2018, a search ship vanished without explanation

Late in January 2018, a ship that was searching for MH370 turned off its tracking screens and was undetectable for three days during its search. This prompted a flood of questions about the ship, its knowledge of the plane, and its intentions. Neither the Malaysian government or Ocean Infinity explained the reason for the ship’s disappearance. It has since lead to even more conspiracy theories surrounding the plane.

Next: Families of those on MH370 have recently protested about this.

Families of those presumed lost have protested against a memorial

In March 2018, Australia announced that it would put up a memorial for MH370. The Australian government said it would honor the 239 people on board and be completed in September 2018. The memorial got strong opposition from the next of kin of those on the flight. Since the mystery has not yet been solved, family members urge that it’s too early to put up a memorial.

Family members of Chinese passengers have said it is a curse to put up a memorial before people are confirmed dead.

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