I just ran across one theory, which doesn't seem like it would hold much water: The Electronic Fog. I quote:
The first indication the airliner may have been in trouble is when the co-pilot signed off from Malaysian air traffic control. He said �all right good night 370.� Normally he would say something like �Malaysian 370 contacting Viet Nam at 128.4 thank you goodnight.� Maybe the electronic fog had just attached itself to the aircraft so he cut the procedure short. They never contacted Viet Nam airspace and strange things started happening immediately after that last call. The fog can disable the radios. The Boeing 777 has a glass panel cockpit. All the panels could have turned off and turned blank. The pilots would have no idea of their exact heading because even the whisky compass would be spinning. They would have to rely on their mechanical backup instruments to maintain control. They are the altimeter, the airspeed indicator and the attitude indicator.I think a better supported theory is that of Marc Dugain:
They made about a 120 degree turn to the left, apparently trying to aim for the nearest airport. It appears they went up higher trying to get above the fog and down lower trying to get below the fog but it did not detach. When the time came to the point where they should be able to identify the airport there was no visibility. They made some more turns and that would have disoriented them to the point where they are not sure of their heading anymore. Many pilots that have been in the electronic fog that crashed, went through a series of turns then became spatially disoriented and ended up entering what is known as a graveyard spiral which always ends up in death.
They may have been able to control the autopilot but the heading would have to be controlled by their input. After going through a series of turns they would be becoming disoriented so they did something similar to Flight 19. They just continued until they ran out of fuel. Also like Flight 19 they unfortunately aimed for a remote location over the ocean where they may never be found.
Dugain, a well-respected French author, argues that the Boeing 777 carrying 239 people crashed near Diego Garcia, a British island in the middle of the Indian Ocean used as a strategic air force and intelligence base by the US military, in the six-page article in Paris Match.
The US has always officially denied that flight MH370 came anywhere near Diego Garcia.
The latest theory into the disappearance of Malaysian Airlines flight MH370 on March 9, 2014 has all the ingredients of a spy thriller and has grabbed the French public’s attention. The former boss of Proteus Airlines travelled to the neighbouring Maldives where residents told local media on March 9th that they had seen an airliner fly in the direction of Diego Garcia. Their claims were promptly dismissed by the authorities.
“I saw a huge plane fly over us at low altitude,” a fisherman on Kudahuvadhoo island told Dugain. “I saw red and blue stripes on a white background” – the colours of Malaysia Airlines. Other witnesses confirmed the sighting.
Dugain speculates – adding to the numerous other existing hypotheses about what happened to flight MH370 – that a modern aircraft such as Malaysia Airlines' Boeing 777 could have been hijacked by a hacker. “In 2006, Boeing patented a remote control system using a computer placed inside or outside the aircraft,” he noted. This technology lead Dugain to the idea of a “soft” remote hijacking. But the writer also suggests that a fire could have led the crew to deactivate electrical devices, including transmission systems.
Whatever the initial reasons for leaving its flight path, Dugain suspects that the plane then headed to Diego Garcia, where a number of scenarios may have played out – including the US Air Force shooting it down for fear of a September 11-style attack. Dugain met the mayor of neighbouring Baarah island, who showed him pictures of a strange device found on a beach two weeks after the plane had disappeared and before the Maldives military seized it. Two aviation experts and a local military officer concluded that the object was a Boeing fire extinguisher. Dugain points out that for the extinguisher to have floated, it must have been empty, having been automatically triggered by a fire. He adds that precedent exists in which fires on board aircraft caused all passengers and crew to die of asphyxiation, while the plane’s automated systems extinguished the blaze and kept it in the air.Okay, so we have no direct evidence of an Electronic Fog, but we do have indirect evidence of a fire on board a Boeing aircraft--along with eyewitness testimony of just such an aircraft, bearing the Malaysian livery, being where it did not belong. We know that Diego Garcia is a strategically important air base, in the center of a very strictly enforced restricted zone. By the way, the rumour that Philip Wood was imprisoned there was a cruel hoax, and easily refuted. But no one, apparently, has tried to refute the eyewitness testimony and fire extinguisher, both of which place the airliner within shoot-down range of the Naval Air Facility.
This is what apparently happened: The US shot down the plane when it looked like it was on a suicide run toward the most important US base within a thousand miles. Unsure of what they had hit, government forces didn't say anything at first, but worked to misdirect the search effort long enough to make sure they had cleaned up the crash scene. Then, realizing they could sweep the whole operation under the rug, they kept up the cover-up to this day.
You can count on official disinformation whenever there is a cover-up, and here we have it. Taking a page from the Soviet's Flight 007 playbook, a US submersible faked a sonar ping from the airliner's black box, leading search efforts to concentrate thousands of miles from where the plane was actually shot down. Everything that came out of the US role in the 'search effort' was misinformation from that point on.
This still doesn't address the question of why Flight 370 was misdirected, but the fact that the pilot had practiced simulator landings on Diego Garcia, combined with his Islamic world view, shows a man with the method, means, and motivation to set back the US War on Terror for years to come.
If he really was targeting NAF DG, there's no reason why he shouldn't have been shot down; since 9/11, it is official USG policy to shoot down a passenger jet in such a scenario. But why admit that they did, when it turned out to be so easy to leave everything a big mystery?