Vanished Malaysia Airlines Flight MH370 Still a Mystery 1 Year Later

— -- A year after it vanished, there still is no trace of Malaysia Airlines Flight MH370, which many believe disappeared into the abyss of the Indian Ocean.

Theories of what happened to the plane have been swirling ever since, but no one really knows what occurred.

"I am a little surprised that we haven’t had something wash up on a beach that would tell us, yes, the airplane was in pieces, and was in the water," said John Nance, ABC News aviation contributor. "I think that is still probably going to happen."

The Boeing 777 left Kuala Lumpur, Malaysia, en route to Beijing on March 8, 2014, when it lost contact with air traffic control as it flew over the Gulf of Thailand. The jet had 227 passengers, most of whom were Chinese, along with 12 crew members.

Here are some of the many open questions a year later:

How did it happen?

Investigators believe the plane flew thousands of miles off course before crashing into the Indian Ocean. Australian officials still looking for the plane or its remnants say they are focusing on a search area of approximately 23,000 square miles west of the Australian city of Perth, and hope to find something that will provide answers to the plane's fate.

"The flight data recorder might be very helpful, certainly -- very helpful in terms of how the airplane entered the water," Nance said.

Where is the plane is located?

Malaysian authorities say the plane disappeared about an hour after it took off. However, no one is sure where the plane crashed, or even if it crashed at all. Some believe the plane is located in the southern part of the Indian Ocean, while others believe it flew into the northern part.

Speculation that the plane went north doesn't make sense to Nance, because it discounts evidence from satellite tracking systems. He added that finding the plane may be difficult because the southern Indian Ocean is a large body of water that is mostly unmapped.

What happens next?

Australia said it will continue to search for the plane.

Australian Deputy Prime Minister Warren Truss said in a statement to Reuters on Sunday, "We clearly cannot keep searching forever, but we want to do everything that's reasonably possible to locate the aircraft."

Truss's office added it was optimistic about finding the plane, given that over 40 percent of the priority search area has already been covered.

If the plane isn't found by the completion of the search, the deputy prime minister’s office told Reuters, discussions will then be had between Australia, Malaysia and China about what to do next.

“If at the end of the search, there is nothing that has been found, I think it’s going to be very difficult for everybody,” Nance said.

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