Over the past 10 days, investigators and observers have come up with ever more elaborate theories for what might have happened to Malaysia Airlines Flight 370.

What was originally assumed to have been a tragic midair explosion or mechanical problem soon bloomed into a criminal investigation of a meticulously planned hijacking, commandeering, or otherwise stealing of a fully loaded commercial 777 in midair.

The perpetrator(s) knew the plane so well, one of the latest theories goes, that they climbed through a trap door outside the cockpit to reach circuit breakers necessary to shut down one of the communications systems. They shut down the transponder. They made the plane disappear and fooled the world into thinking it had crashed. They flew one of two "arcs" for seven hours — a "southern route" over the Indian Ocean on which, eventually, they crashed the plane in the ocean in a complicated suicide, and a "northern route" in which, perhaps, they slipped past land-based radar, flew to a destination in central Asia, and landed, perhaps preparing to use the plane again soon for a terrorist attack or other mission. This latter plan was executed so flawlessly, one observer theorized, that Flight 370 slipped in behind another commercial airliner for much of the route so as not to be noticed on radar.

The pilots' houses have been searched. Terrorist connections have been investigated. Passenger backgrounds and possible motives have been scrutinized. And still, 10 days after the plane disappeared, we know nothing.

Perhaps that's because we're overthinking it.

A few days ago, a former pilot named Chris Goodfellow articulated an entirely different theory on Google+.

This theory fits the facts.

And it's one of the most plausible yet:

Shortly after takeoff, as Malaysia 370 was flying out over the ocean, just after the co-pilot gave his final "Good night" sign-off to Malaysia air traffic control, smoke began filling the cockpit, perhaps from a tire on the front landing gear that had ignited on takeoff.

The captain immediately did exactly what he had been trained to do: turn the plane toward the closest airport so he could land.

The closest appropriate airport was called Pulau Langkawi. It had a massive 13,000-foot runway. The captain programmed the destination into the flight computer. The autopilot turned the plane west and put it on a course right for the runway (the same heading the plane turned to).

The captain and co-pilot tried to find the source of the smoke and fire. They switched off electrical "busses" to try to isolate it, in the process turning off systems like the transponder and ACARs automated update system (but not, presumably, the autopilot, which was flying the plane). They did not issue a distress call, because in a midair emergency your priorities are "aviate, navigate, communicate" — in that order. But smoke soon filled the cockpit and overwhelmed them (a tire fire could do this). The pilots passed out or died.

Smoke filled the cabin and overwhelmed and distracted the passengers and cabin crew ... or the cockpit door was locked and/or the cockpit was filled with smoke, so no one could enter the cockpit to try to figure out where the plane was, how the pilots were, or how the plane might be successfully landed. (This would be a complicated task, even if one knew the pilots were unconscious and had access to the cockpit, especially if most of the plane's electrical systems were switched off or damaged).

With no one awake to instruct the autopilot to land, the plane kept flying on its last programmed course ... right over Pulau Langkawi and out over the Indian Ocean. The engine-update system kept "pinging" the satellite. Eventually, six or seven hours after the incident, the plane ran out of fuel and crashed.

This theory fits the facts. It makes sense. It explains the manual course change as well as the "pings" that a satellite kept hearing from the plane. It requires no fantastically brilliant pre-planning or execution or motives.

Here's Chris Goodfellow:

A lot of speculation about MH370. Terrorism, hijack, meteors. I cannot believe the analysis on CNN - almost disturbing. I tend to look for a more simple explanation of this event.



Loaded 777 departs midnight from Kuala to Beijing. Hot night. Heavy aircraft. About an hour out across the gulf towards Vietnam the plane goes dark meaning the transponder goes off and secondary radar tracking goes off.



Two days later we hear of reports that Malaysian military radar (which is a primary radar meaning the plane is being tracked by reflection rather than by transponder interrogation response) has tracked the plane on a southwesterly course back across the Malay Peninsula into the straits of Malacca.



When I heard this I immediately brought up Google Earth and I searched for airports in proximity to the track towards southwest.



The left turn is the key here. This was a very experienced senior Captain with 18,000 hours. Maybe some of the younger pilots interviewed on CNN didn't pick up on this left turn. We old pilots were always drilled to always know the closest airport of safe harbor while in cruise. Airports behind us, airports abeam us and airports ahead of us. Always in our head. Always. Because if something happens you don't want to be thinking what are you going to do - you already know what you are going to do. Instinctively when I saw that left turn with a direct heading I knew he was heading for an airport. Actually he was taking a direct route to Palau Langkawi a 13,000 foot strip with an approach over water at night with no obstacles. He did not turn back to Kuala Lampur because he knew he had 8,000 foot ridges to cross. He knew the terrain was friendlier towards Langkawi and also a shorter distance.



Take a look on Google Earth at this airport. This pilot did all the right things. He was confronted by some major event onboard that made him make that immediate turn back to the closest safe airport.

For me the loss of transponders and communications makes perfect sense if a fire. There was most likely a fire or electrical fire. In the case of fire the first response if to pull all the main busses and restore circuits one by one until you have isolated the bad one.



If they pulled the busses the plane indeed would go silent. It was probably a serious event and they simply were occupied with controlling the plane and trying to fight the fire. Aviate, Navigate and lastly communicate. There are two types of fires. Electrical might not be as fast and furious and there might or might not be incapacitating smoke. However there is the possibility given the timeline that perhaps there was an overheat on one of the front landing gear tires and it blew on takeoff and started slowly burning. Yes this happens with underinflated tires. Remember heavy plane, hot night, sea level, long run takeoff. There was a well known accident in Nigeria of a DC8 that had a landing gear fire on takeoff. A tire fire once going would produce horrific incapacitating smoke. Yes, pilots have access to oxygen masks but this is a no no with fire. Most have access to a smoke hood with a filter but this will only last for a few minutes depending on the smoke level. (I used to carry one of my own in a flight bag and I still carry one in my briefcase today when I fly).



What I think happened is that they were overcome by smoke and the plane just continued on the heading probably on George (autopilot) until either fuel exhaustion or fire destroyed the control surfaces and it crashed. I said four days ago you will find it along that route - looking elsewhere was pointless.



This pilot, as I say, was a hero struggling with an impossible situation trying to get that plane to Langkawi. No doubt in my mind. That's the reason for the turn and direct route. A hijack would not have made that deliberate left turn with a direct heading for Langkawi. It would probably have weaved around a bit until the hijackers decided on where they were taking it ...

Chris Goodfellow's full explanation for his theory is here. It's the simplest and most compelling I've heard yet.

UPDATE: We reached out to a couple of 777 pilots to ask what they thought of this theory. They were skeptical. They said the first course of action on a "smoke and fumes" checklist is to put on an oxygen mask — even before turning the plane toward a runway. More details here...