On March 8, 2014, Malaysian Airlines flight MH370 disappeared as it traveled to Beijing, China from Kuala Lumpur, making it one of aviation’s greatest unsolved mysteries.

On that day at 00:41 Kuala Lumpur time the plane carrying 239 passengers took off from the Kuala Lumpur International Airport and was scheduled to arrive in Beijing at 06:30 on the same day.

“Good night Malaysian three seven zero” was the last message received by the Malaysian Air Traffic Controller at 01:19. It was the co-pilot Fariq Hamid who uttered the last correspondence, not Zaharie Ahmad Shah, the pilot.

Two minutes later, the plane disappeared from air traffic control’s screen as the transponder was shut down. The Malaysian authorities at first believed that someone in a cockpit de-activated a communication system and diverted the plane.

Despite an extensive search effort worth $155 million – the most extensive search in aviation history – the body of the doomed plane was never found, some debris was discovered off the coast of Africa.

The official search for MH370 was terminated, but the mystery surrounding the incident still lingers. The following is a list of the various theories – ranging from the probable to the far-fetched – on the disappearance of the missing Boeing 777:

MH370 Pilot Factor

One of the earliest theories was that the MH370 pilot Zaharie Ahmad Shah was under mental pressure and deliberately crashed the plane off.

John Cox, an aviation safety expert, cited data radar showing that the plane was drastically diverted from the initial route from Kuala Lumpur to Beijing and went back across the Malaysian Peninsula.

“I think it was a deliberate act, if you look at an accident, and you as an investigator are tasked to determine what the probable cause of the accident is, then I think you say the probable cause of the accident was the result of a deliberate act,” Cox a pilot with 14,000 hours of flight time told The Daily Star.

Last year, a similar claim also emerged when a global aviation expert told Australia’s TV program “60 Minutes” that Ahmad Shah committed suicide by crashing the plane that also killed 238 souls. But, again, evidence to support this theory was sparse.

On “60 Minutes” Boeing 777 senior pilot Simon Hardy said Ahmad Shah deliberately flew the plane above his hometown Penang, as if he wanted to say goodbye and directed the airliner to the southern part of the Indian Ocean, in a location that was never found.

Another theory said that Ahmad Shah hijacked the plane he flew to protest the imprisonment of Malaysia’s opposition leader Anwar Ibrahim and ruin the then Najib Razak administration, which was plagued by a graft case.

In 2016, Malaysian officials said Ahmad Shah had planned a flight path over the Indian Ocean through a simulator at home. But this fact did not prove to be related to the tragedy.

The Australian Transport Safety Bureau (ATSB) dismissed claims that the MH370 pilot deliberately plunged the plane, saying that the airliner lost control when it dove into the Indian Ocean.

Did Terrorism Take Down MH370?

There are speculations that the plane was hijacked by terrorists. One of the supporters of this claim was media mogul Rupert Murdoch, who tweeted that the MH370 was probably stolen and hidden in Pakistan.

The alleged terrorism-related theory seemed to have some credibility as a few days before the plane went missing, Taiwan’s National Security Department admitted receiving a bomb threat targeting the Beijing International Airport. However, it was determined the threat was not related to the MH370 saga.

Three days after the plane’s disappearance, Interpol said based on the information the organization received, the missing plane had nothing to do with the terrorist plot.

Later evidence showed that one of the two Iranian-descent passengers aboard the plane used a stolen passport to go to Germany to see his mother. But the investigation revealed that neither of the Iranian men were connected to any terrorist organizations, adding that both were only illegal passengers who tried to go to Beijing before seeking asylum in Germany. Malaysia also snubbed the claim that the plane was hijacked by terrorists.

Mechanical Failure Causing Hypoxia

Another theory was that a fire may have broken out in the cockpit, producing smoke that knocked passengers unconscious due to hypoxia which is a lack of oxygen supply.

The term and idea of a “mass hypoxia” event onboard the plane was supported by several analysts. It is possible that Flight MH370 could have continued to fly for hours after it caught on fire and everyone was dead, said a retired pilot Captain Aimer Ross. The plane would then have run out of fuel and crashed.

“The fire may have started during or shortly after takeoff since things started to happen as soon as they leveled off. It is possible the fire killed everyone onboard then continued burning the aircraft until it crashed. Since the flaperon was discovered in the ocean, it most probably crashed into the ocean,” said a former United Airlines pilot.

However, others disputed this as they said there still should have been a distress call.

“Typically, with an electrical fire, you’ll have smoke before you have fire,” said Greg Feith, a former NTSB crash investigator to NBC News. “You can do some troubleshooting. And if the systems are still up and running, you can get off a mayday call.”

Some of the maneuvers long after the plane lost contact also suggested a human was still at the controls.

“While it’s true that MH370 did turn toward Langkawi and wound up overflying it, whoever was at the controls continued to maneuver after that point as well, turning sharply right at VAMPI waypoint, then left again at GIVAL,” said Jeff Wise in Slate magazine. “Such vigorous navigating would have been impossible for unconscious men.”

Mysterious Extra Passenger Theory

Flight MH370 was carrying a mysterious extra passenger who probably took over the plane before it went down in the Indian Ocean, according to an investigation revealed in a lawsuit filed by families of 44 victims of the fallen plane.

The Malaysia authorities claimed MH370 was carrying 239 passengers, but the plane’s manifest showed that the official number of passengers was 226, plus 12 crew makes the total passengers on board 238.

According to a spokesperson for the MH370 safety investigation team, the actual number of passengers was 227. The manifest which said 228 passengers were on board was a computerized count transmitted two hours before the plane took off.

‘The actual figures can differ from that transmitted on the load sheet due to last minute changes,” the spokesman said.

Russian Involvement

Four years ago, aviation expert Jeff Wise theorized that MH370 was hijacked and taken to a Russian military base in Kazakhstan where all the passengers were held as hostages. The expert alleged Russia aimed to protest western intervention in the Ukraine conflict. Russia dismissed the claim.

Another investigator also claimed that Russia’s president Vladimir Putin knew exactly where the missing plane was. Andre Milne told Daily Star that the MH370 flight made a soft ditch landing in the Bay of Bengal in the Indian Ocean.

Milne added that spy satellites placed by Russia above the Indian Ocean detected the doomed airliner’s debris.

The reason President Putin did not raise his hand and march in and say we found it is because technically he would have been admitting committing espionage,” Milne said.

Problems with Cracks

Six months before the airliner went missing, U.S. Aviation Watchdog warned several airline firms that Boeing 777s airliners had problems with cracks that could cause a catastrophic drop in pressure.

The Federal Aviation Agency issued its last warning two days before the MH370 vanished when a 15-inch crack was seen in the body of a Boeing 777 in North America.

Cyber Hijacking

World-renowned historian and author, Norman Davies, said that a technology designed to prevent terrorist attacks similar to 9/11 could have allowed cybercriminals to control MH370 remotely.

In his book Beneath Another Sky: A Global Journey into History, Davies claimed that the missing jet was equipped with Boeing Honeywell Un-interruptible Autopilot computers on-board, which could be hijacked and later reprogrammed to be taken to a secret place.

MH370 might have been carrying “sensitive” materials or persons to Beijing, making it vulnerable to abduction attempts.

A new documentary related to MH370 featured cyber defense expert Chris Roberts who also claimed that the plane was hacked.

“A determined hacker with the right tools and the right knowledge of a 777 would have the ability to go through the cabin system, to the cockpit system and influence the flight.

“The in-flight entertainment system is connected to a box that is just underneath the seats,” Roberts said in a 2018 documentary.

MH370 Was Gunned Down

In March 2018, an Australian mechanic engineer claimed to have found debris of MH370 via Google Earth.

Peter McMahon spent years combing the Indian Ocean via Google Earth to find the debris of the doomed jet. Mahon said the wreckage was full of bullet holes and located a few miles off of the southern end of Round Island, which is governed by Mauritius.

However, Malaysia and the ATSB said that McMahon’s claims were baseless and that the images Mahon used as claims were taken four years before the MH370 tragedy.

MH17 and MH370 are the Same Planes

Around four months after MH370 went missing, Malaysian Airline flight MH17 from Amsterdam to Kuala Lumpur was shot down in Ukraine. The two tragedies happening so closely together shocked the aviation industry. While MH17 and most of its passengers were found near the location where it was shot, the MH370 wreckage has never been discovered.

Amateur sleuths have claimed that MH370 was really MH17 and was thus shot down in Ukraine. Some have added that MH370 was shot down by Israel’s intelligence agency Mossad to cover crimes the Jewish state committed in Gaza. But, the claims had no supporting evidence.

In a reversal, another amateur investigator, Daniel Boyer, claimed that the debris officials say is from the crash of MH370 was actually that of MH17, but again, this theory is not proven to be accurate.

“However there are too many inconsistencies, such as the lack of marine life on the debris.

“The debris found had little to no barnacles. Barnacles that were scientifically tested in labs were no older than three weeks old, raising suspicion of the fact these objects floated for over a year,” Boyer stated.

“There is one major clue where Item 22 from the vertical wing claimed to have washed up from MH370 coincidentally fits onto a missing part of the vertical wing of the MH17 flight.

“This draws suspicion since the likeliness of a plane part to wash up and fit exactly like a puzzle to another plain’s missing puzzle piece is extremely unlikely.”

Diego Garcia, US Military Shoots Down MH370

A French former airline director said in a French magazine that MH370 did not vanish, but landed on a mysterious island called Diego Garcia which is a U.S military base in the Indian Ocean.

He added that the plane may have been deliberately shot down by U.S. military due to concerns that MH370 was approaching the military base in a 9/11 style attack.

“It’s an extremely powerful military base. It’s surprising that the Americans have lost all trace of this aircraft. Without getting into conspiracy theories, it is a possibility that the Americans stopped this plane,” he told France Inter, according to a translation by The Local.

The conspiracy theory went viral, but Washington has denied the accusation.

Lessons Learned From the Loss of MH370

While families of MH370 victims are still hoping one day for answers to the disappearance of MH370, the tragedy has also propelled the aviation sector to install new tracking technology that could prevent such a repeat mystery.

“Not only will these tracking systems save the world from losing another plane and the heartbreak of five years out still not knowing where the people are, but every month it will save a state, a country, another jurisdiction from having to search for small planes that go missing all the time,” CNN aviation expert Mary Schiavo said.

Aviation analysts claim that the new technology combines more advanced black boxes with more affordable and new satellites that will make it easier to follow planes and get access to flight data after the incident. However, the implementation of the new system will vary country by country as no accepted standards have been set up by the international aviation body.

There is hope for family members of MH370 victims that officials will continue to investigate MH370. Last Sunday, Malaysia’s Prime Minister Mahathir Mohamad met a family member of one victim, telling them, “we intend to continue the search.”

This is the first time Malaysian Prime Minister Mahathir bin Mohamad has met with a relative of a MH370 victim, listening to the desperate plea of Danica Weeks to continue the search for the missing plane. #60Mins pic.twitter.com/pkQIIj0OWG

— 60 Minutes Australia (@60Mins) March 3, 2019