Crash investigators have numerous avenues to investigate in the disappearance of Malaysia Airlines Flight 370, even as an international search effort for the plane continues off the coast of Vietnam, a U.S. crash probe expert said Monday.
The fate of the missing Beijing-bound jet, which disappeared early Saturday with 239 people aboard, remained a mystery after the latest possible clues to the plane's whereabouts were discounted.
Tests on two oil slicks off the coast of Vietnam revealed no connection to the flight, investigators said. And a piece of floating, yellow debris turned out to be moss-covered trash; another piece seen from the air Sunday night could not be located Monday.
At a press briefing on Phu Quoc Island, Vietnam Deputy Minister of Transport Pham Quy Tieu said a third day of search and rescue operations came up empty.
"Sadly, we have had no positive signs of the Malaysian plane," he said Monday.
Tom Anthony, a former regional investigations manager for the Federal Aviation Administration, told USA TODAY that crash investigators still have plenty of work to do. Authorities will want to check everyone and everything that went on the plane, he said.
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"Any aircraft accident like this is like a big jigsaw puzzle," said Anthony, who is now head of the aviation and security program at the University of Southern California. "In this case, all the pieces of the puzzle are not on the bottom of the ocean. They are open and available to us."
Two of the passengers aboard the Boeing 777 were traveling on stolen passports. But records of luggage, cargo and business property aboard the plane — and along with maintenance records about how the plane was handled before it took off — could also be scrutinized before wreckage is found, Anthony said.
"There is lots of things to look at," Anthony said. "Did it contain hazardous materials?"
Luggage could have contained a possible explosive or hazardous material. So could cargo, such as poorly packed lithium batteries. So-called "business property" aboard the plane could include oxygen generators — similar to those that were improperly stored and blamed in the ValuJet Flight 592 crash in Florida in May 1996.
Meanwhile, investigators will want to speak to the crew that flew the 777 before this flight, to see if any maintenance problems were reported, Anthony said.
They will also check whoever came into contact with the plane and document what maintenance occurred before the flight, he said.
"There's a lot that can be done at the airport and on databases," Anthony said. "Many of the devices that are used to prepare the plane for flight have electronic memory in them. They are still available."
The search for the aircraft is complicated because of multiple countries: the plane is part of the Malaysian national carrier; the Vietnamese government is assisting the search because of where radar lost track of the plane; and the Chinese government because most of the passengers were headed to Beijing.
The U.S. National Transportation Safety Board has sent a team to lend expertise investigating the incident.
Agreements within the United Nations called the International Civil Aviation Organization, based in Montreal, set standards for how the investigation will be conducted. Multiple governments are often involved in plane crashes, which Anthony called "difficult, but typical."
The lead investigator isn't expected to be named until wreckage is found. But Malaysia could defer to another country, as happened with the EgyptAir flight 990 crash in October 1999. That crash off the coast of Massachusetts fell to Egyptian authorities, under ICAO rules, but that country asked the NTSB to investigate, citing its own lack of resources.
The U.S. doesn't always lead investigations. Swissair Flight 111, which operated under a code-share agreement with Delta Air Lines, crashed in September 1998 off Nova Scotia and the Canadian government investigated.
"Countries can request assistance or transfer whole control to another party," said John Goglia, a former NTSB investigator.
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Thomas Maresca reported from Vietnam. Contributing: Calum MacLeod from Beijing, John Bacon from McLean, Va.; Associated Press