The two possible paths have the plane heading toward the South Pole and ending, experts believe, off of Australia.
U.S. officials familiar with the investigation tell ABC News that the hourly satellite pings from the jet had yielded far more clues than expected, enabling the focus of the search to be cut in half - from an area roughly the size of Texas to that of Arizona.
Calculations by UK and US experts had now been handed over to the Australians to help with the search.
Flight MH370 departed Kuala Lumpur at 12:55 a.m. Friday, and was scheduled to land in Beijing at 6:30 a.m., the airline said. It disappeared two hours into the flight and disappeared off the radar northwest of Kota Bharu, Malaysia, in the South China Sea.
There were 227 passengers and 12 crew on board.
The Australians have their aircraft concentrating around the two plot lines and a new high-tech subhunter called P-8 is also flying missions, looking for any wreckage in the vast areas.
Earlier today, ABC News learned that the FBI is examining the homemade flight simulator that belonged to the captain of the missing Malaysia Airlines flight and a key question will be trying to determine what the captain deleted and whether it's important to the investigation.
The simulator's hard drive and data were taken from the home of Capt. Zaharie Ahmad Shahthis week as part of investigators' efforts to determine whether the crew of the plane could have been complicit in whatever happened to the flight and the 239 people on board. Authorities are baffled about the plane's disappearance, but have determined that it was a "deliberate act."