The search for Malaysia Airlines Flight 370 is now in its tenth day, and as authorities attempt to make sense of the plane's disappearance, and family members grapple with the likely loss of its 239 passengers, the internet is hard at work trying to figure out what happened. Some theories are obviously wrong (aliens?). Some are just probably wrong—but their plausibility has led to widespread dissemination online. Here are four of the least crazy-sounding:

The crew disabled the plane's communications system because of a fire. The smoke from the fire eventually knocked everyone unconscious, and the plane, which had been traveling on autopilot, crashed once it ran out of fuel.

This theory has been advanced by pilot Chris Goodfellow:

If they pulled the [electrical] 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 under inflated 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.

Sounds terrifying—but also very possible! Then again, Goodfellow wrote the post before Malaysian authorities announced their hijacking theory on Saturday.

"I wrote this post before the information regarding the engines continuing to run for approximately six hours and the fact it seems acars was shut down before the transponder," Goodfellow wrote in his comments.

His suggestion that the plane would have flown erratically in the case of a hijacking has irked some. From Jalopnik:

Would hijackers really seize control of a massive jet with over 200 people on board with no planned destination? Absolutely not. They would immediately demand to be flown somewhere very specific.

And one former pilot told Business Insider that, before dumping the communications system, he "would have communicated their emergency and intentions to turn around, as well as ask for assistance and direct routing to a suitable airport from the air traffic controllers very quickly."

The plane crashed in a pilot's suicide attempt.

Some pilots and aviation officials believe pilot suicide is the most likely explanation for Flight 370's disappearance.

In an interview with CBS News, Mike Glynn, a committee member of the Australian and International Pilots Association, pointed out that pilot suicides are suspected as causes in for the 1997 SilkAir crash and an EgyptAir crash in 1999.

"A pilot rather than a hijacker is more likely to be able to switch off the communications equipment,'' Glynn told CBS News. "The last thing that I, as a pilot, want is suspicion to fall on the crew, but it's happened twice before.''

There are also more outlandish theories on reddit (of course) supporting the pilot suicide idea.

Flight 370 flew behind another airplane in the area, hiding it from radar and allowing it to land elsewhere undetected.

This one, proposed by hobby pilot and aviation enthusiast Keith Ledgerwood, was making the rounds on Tumblr earlier this week. It seems to make sense; there are certainly lots of maps and charts, and some knowledgeable-sounding jargon. Here's the crux:

There are too many oddities in this whole story that don't make sense if this theory isn't the answer in my opinion. Why did MH370 fly a seemingly haphazard route and suddenly start heading northwest towards the Andaman Islands on P628? If not for this reason, it seems like a rather odd maneuver. The timing and evasive actions seem deliberate. Someone went through great lengths to attempt to become stealthy and disable ACARS, transponder/ADS-B (even though SATCOM to Inmarsat was left powered).

After looking at all the details, it is my opinion that MH370 snuck out of the Bay of Bengal using SIA68 as the perfect cover. It entered radar coverage already in the radar shadow of the other 777, stayed there throughout coverage, and then exited SIA68's shadow and then most likely landed in one of several land locations north of India and Afghanistan.

Sure, why not!

Courtney Love found the plane.

Sure, some people claim to have disproved Love's theory. But we still believe, Courtney.

And here's what we (think) we know for sure about what happened: The flight was reportedly rerouted by a pre-programmed computer system just after its final communication ("all right, good night") with Malaysian air control. After reviewing military data showing that it soared above 45,000 feet, Malaysian officials believe the plane, which reportedly flew for hours after it vanished from civilian radar, was either hijacked or sabotaged.

[Image via Getty]