Nearly three days after the last contact with the missing Malaysia Airlines jet, officials Sunday tied their hopes to small bits of debris and said they would scour a wider expanse of the sea in search of the vanished aircraft — even as many experts said it could take investigators months, or even years, to find out what happened to Flight 370.
Here are the main questions about the search operations underway:
Who will lead the investigation?
It has yet to be decided which country's aviation safety agency will spearhead the investigation into what happened to Flight 370 — since it has yet to be determined exactly where the Boeing 777 is.
But if the aircraft is found, International Civil Aviation Organization (ICAO) protocols will determine which nation leads the probe, according to a statement from the National Transportation Safety Board, the U.S. federal agency.
Still, Capt. John M. Cox, who spent a quarter-century flying for U.S. Airways and who is now CEO of Safety Operating Systems, told NBC News Sunday that no matter which country heads up the investigation, it is likely to be a joint effort.
If the aviation safety agencies of Malaysia or Vietnam are in the lead, they may ask for help from one of five different countries — the U.S., France, the United Kingdom, Canada or Australia, according to Cox. The jet, which was carrying 239 people, lost contact with ground controllers somewhere between Malaysia and Vietnam.
And joint investigations are not unprecedented. After Air France Flight 447 from Rio de Janeiro to Paris plunged into the Mid-Atlantic in 2009, killing 228 people, Brazil asked the French aviation safety bureau for help, Cox noted.
Who is already providing assisstance?
A total of 40 ships and 22 aircraft were scouring for the vanished jet Sunday, Cmdr. Williams J. Marks, public affairs officer for the U.S. 7th Fleet, told NBC News.
The U.S., Malaysia, Vietnam, Thailand, Singapore, Indonesia, China, Australia and the Philippines have all contributed to search operations, the Malaysia government has said, according to an official at the U.S. Embassy in Kuala Lumpur.
What is the U.S. role?
Tom Blinken, President Barack Obama's deputy national security adviser, said on NBC's "Meet the Press" Sunday that the U.S. government is "actively looking into all questions" raised by the disappearance of the missing flight.
He told NBC's David Gregory that officials from the NTSB, the Federal Aviation Administration and the FBI will be "heading to the area to help in the investigation."
"Lots of questions have been raised. We don't have all the answers yet. We'll get them," Blinken said.
The U.S.S. Pinckney, a destroyer dispatched by the U.S. 7th Fleet, was scouring waters Sunday around the last known positions of Flight 370, Marks told NBC News.
The destroyer arrived Sunday with two key Navy aircraft — the P-3 Orion and an MH-60R helicopter, Marks said.
The Orion, which conducts extended searches that last between nine and ten hours, is slated to go out again at 9 a.m. Hong Kong time Monday (9 p.m. ET Sunday), according to Marks.
Where are rescue teams looking?
Officials said Sunday they were widening the search to cover vast swathes of sea around Malaysia and off Vietnam.
Vietnamese naval boats sent from the holiday island of Phu Quoc patrolled stretches of the Gulf of Thailand, scouring the area where an oil slick was spotted by patrol jets just before nightfall Saturday.
The search was being extended to the west coast of the Malay peninsula, in addition to a broad expanse of the sea between Malaysia and Vietnam, Malaysian air force chief Rodzali Daud said.
All told, the expanse of sea being scoured Sunday "easily spans hundreds of square miles," according to Marks.
What are experts' preliminary theories?
"At this early stage, we're focusing on the facts that we don't know," Todd Curtis, a former Boeing safety engineer who worked on its 777 wide-body jets and is now director of the Airsafe.com Foundation, told The Associated Press.
Military radar indicates that the missing Boeing 777 jet may have turned back before vanishing, Malaysia's air force chief said Sunday.
Daud didn't say which direction the plane might have taken or for how long when it apparently went off route. "We are trying to make sense of this," he said at a news edia conference. "The military radar indicated that the aircraft may have made a turn back, and in some parts, this was corroborated by civilian radar."
Courtney Kube, Jay Blackman, Tom Curry and Pete Williams of NBC News contributed to this report.