Business Insider published an article called ''The most plausible theory for the plane disappearance'' where it cites the opinion of former pilot Chris Goodfellow.
He wrote on Google Plus that, in his opinion, just before the plane disappeared from the radars, one of the landing tires caught fire which caused the cabin to fill with smoke.
The alerted pilots turned the plane to the nearest airport where landing would be possible, called Pulau Langkawi. That explains the deviation from the original route.
Then, the pilots tried to find the source of the fire, which is why they closed most
The reason why the pilots have not contacted the ground is that if a problem occurs, communication with the control towers is not the priority, but solving the problem and maintaining the aircraft on the route is.
So before they got to communicate with the ground, the pilots probably fainted or died, says Goodfellow.
Then, the plane continued flying on autopilot, passed over Pulau Langkawi airport because there was nobody to land it, flew until the fuel was over and plunged into the Indian Ocean.
Business Insider writes that this is the best theory because it is the easiest and fits with all details known about MH370.