On the riverbank, a group of orange-robed Buddhist monks performed a prayer ceremony for the 30 victims whose bodies have been recovered and those still missing.
Lao Airlines flight QV301 crashed on Wednesday as it prepared to land in stormy weather at Pakse Airport in southern Laos. The plane then skidded into the Mekong River, the largest in Southeast Asia, and disappeared.
All 49 people on board, more than half of whom were foreigners, are presumed dead.
The ATR-72 aircraft was delivered in March, raising questions into why a virtually new plane crashed.
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Until today, the search for bodies and the plane's flight data recorder had been stalled due to lack of manpower and equipment in the poor Southeast Asian country, which lacks capabilities in disaster management.
France's air accident investigation agency, the BEA, said it sent four investigators to help Laos with the probe. It said the team would work with technical advisers from ATR, the French-Italian manufacturer of the aircraft.
The French and Thai teams set out on small boats scanning the water's surface with the sonar equipment today, a stark contrast to previous days of searching that included Lao villagers peering into the murky water from long-tail boats.
Experts say the flight data and voice recorders could help determine if the crash was caused by human error or technical problem.
The chief pilot has been identified as 56-year-old Young San of Cambodia, who had more than 30 years of flying experience.
"Due to a storm and strong winds, as the plan approached landing, the air controller told the pilot to change course," Mak Sam Ol said in a telephone interview. "He followed instructions but the plane faced strong storms and couldn't get through."
According to the airline, 44 passengers and five crew were on the flight. The passengers included 16 Lao nationals, seven French, six Australians, five Thais, three Koreans, three Vietnamese and one person each from China, Malaysia, Taiwan and the United States. A person who had been listed as a Canadian was instead added to the list of Vietnamese.