Missing Boeing 777 mystery: Piracy theory gains more credence

White House spokesman Jay Carney sidestepped questions Friday about the possibility of human intervention in the plane disappearance, saying only that US officials were assisting in the investigation.

"I don't have conclusive answers and I don't think anyone does," Carney said.

Malaysia has faced accusations it isn't sharing all its information or suspicions about the plane's final movements. It insists it is being open, and says it would be irresponsible to narrow the focus of the search until there is undeniable evidence of the plane's flight path.

At this point, there is no evidence of any wrongdoing on the part of the two pilots, though Malaysian police have said they are looking at their psychological background, their family life and connections.

Zaharie Ahmad Shah, 53, and Fariq Abdul Hamid, 27, have both been described as respectable, community-minded men.

Zaharie joined Malaysia Airlines in 1981 and had more than 18,000 hours of experience. His Facebook page showed an aviation enthusiast who flew remote-controlled aircraft, posting pictures of his collection, which included a lightweight twin-engine helicopter and an amphibious aircraft.

Fariq was contemplating marriage after having just graduated to the cockpit of a Boeing 777. He has drawn the greatest scrutiny after the revelation that in 2011, he and another pilot invited two women boarding their aircraft to sit in the cockpit for a flight from Phuket, Thailand, to Kuala Lumpur.

Mike Glynn, a committee member of the Australian and International Pilots Association, said he considers pilot suicide to be the most likely explanation for the disappearance, as was suspected in a SilkAir crash during a flight from Singapore to Jakarta in 1997 and an EgyptAir flight in 1999.

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

Glynn said a pilot may have sought to fly the plane into the Indian Ocean to reduce the chances of recovering data recorders, and to conceal the cause of the disaster.