SYDNEY - Speculation about what happened to Malaysia Airlines Flight MH370 ranges from sober, science-based arguments to outlandish conspiracy theories. Here are some of the most prominent:

The shadow of a Royal New Zealand Air Force (RNZAF) P3 Orion maritime search aircraft can be seen on low-level clouds as it flies over the southern Indian Ocean looking for missing Malaysian Airlines flight MH370 in this March 31, 2014 file photo.[Photo/Agencies]

Crashed in Southern Indian Ocean

Official investigators used analysis from British firm Inmarsat of "pings" to its satellite from MH370, combined with data direct from the plane before it stopped transmissions, to conclude the plane had flown south after it dropped off Malaysian military radar and crashed in the southern Indian Ocean.

The well-respected Independent Group (IG) has done its own analysis and believes the plane is probably near the current search zone, but not necessarily within it.

Just why MH370 ended up there is contested both within IG and others who support the official findings. Some plump for a hijack scenario, others point to technical or pilot error. A British captain, Simon Hardy, says the plane did a fly-by of the pilot's home island of Penang before flying repeatedly in and out of Malaysia and Thailand to confuse air traffic controllers.