Biggest Unsolved Mystery in Aviation | Where is the missing plane? | MH-370

Theories

After these investigations, some theories came forward about what exactly could have happened to the aircraft. 

Suicide Attempt

First they started how could the plane disappear from the radar? Either there'd  be any electric failure in the jet. Or any passenger or pilot intentionally switched of the transponder. Captain Zaharie shah was being accused. It was being said that the captain intentionally disabled the communication and took the plane and crashed it afterwards. But what could be the reason for him to do so? Some people say that he was not in the right mental state. Other people think he was suicidal. There are many reasons to support this theory. The first point is that the aircraft took a 180 degree turn from Vietnam back to Malaysia autopilot is unable to take actions like these. The pilot must have done that manually and intentionally. the second thing is the aircraft was flown between the borders of Thailand and Malaysia. it is said to be the deliberately done so that they could escape the airspace of the both countries. But the officer in charge of this operation completely denied this theory. He said it couldn't be happened because there are many counter-arguments too. He said that the captain was a very highly skilled and a seasonal pilot. He was respected by all. He had no family problems as well. Neither he had an economic problem. So there is doubt to his integrity. 

Hijackings
The second theory that is afloat, is that there must be some hijackers on the plane, They must have done this. When the second theory was raised, a couple of passengers were accused. They were Iranian citizens and they were being suspicious because they were travelling with fake passports. They were travelling with stolen passports. The passports were stolen from Thailand. It has been said that these two men  wanted to use the stolen passport to get settled in Europe. They didn't had any criminal record as well. This theory of hijackings also have been rejected .

Cabin Depressurization 
It is said that and the crew in MH-370 fainted because of oxygen deficiency. Including the pilot and the Co-pilot became unconscious too. In simple words, There were no human life on board. The entire plane actually passed out and kept running on Autopilot. There must have been been some technical malfunction on the Autopilot as well although it was still running. Basically, the Autopilot kept running till it ran out of fuel. And then the plane crashed into the ocean. Now the question is How could this depressurization occurred? Now there are several theories on it. Some people claim that there was a fire in the cockpit and made the systems damage. It is vey much unlikely. Some people blame hijackers here as well. Lets take a possible example to see what might have happened. If I have to cite a typical example of this theory, it is said that as soon as this plane entered Vietnamese airspace the pilot noticed some malfunctions, so the pilot turned the plane 180 degrees too take the plane back to Malaysia. But when the plane started flying towards Malaysia, a terrible accident might have occurred, which led to oxygen deficiency which made everyone in the plane fainted. Several system stopped working and then the plane kept flying on Autopilot. Suddenly the Autopilot turned southwards and kept flying Southwards above the Indian Ocean and crashed into the ocean 2,000 km West of Australia. This is the most logical theory till date.

Other theories
There were many more theories about the plane initially. Such as it was abducted by aliens. Or that the US military stole the plane. Or that the new Bermuda Triangle has been formed at this place. But these are total baseless theories and certainly they are unlikely to happen.