(Bloomberg) -- A team of U.S. airplane accident investigators and technical experts could head to China as soon as this week to help unravel the mysterious crash of a Boeing Co. 737 jet earlier this month, the National Transportation Safety Board said Tuesday.

The Chinese government has issued visas to NTSB investigators, along with technical advisers for the U.S. Federal Aviation Administration and Boeing, the NTSB said on Twitter. Engine maker CFM International, a joint venture of General Electric Co. and France’s Safran SA, will support the probe but isn’t planning to travel.

A Boeing 737-800 operated by China Eastern Airlines Corp. went down in the southern region of Guangxi on March 21 while flying from Kunming to Guangzhou, China’s fifth largest city. All 132 passengers and crew on board perished in the tragedy, the nation’s first commercial jetliner crash in more than a decade.

The U.S. team has been supporting the Civil Aviation Administration of China, which is leading the investigation. Under a United Nations treaty, the country where a crash occurs leads the investigation, while representatives from nations in which the plane and its components were manufactured have a right to participate.

The plane plummeted from its cruise altitude of 29,000 feet (8,840 meters), leveled off once and then appeared to fall straight down. Chinese state media have said the crash left a crater 20 meters deep in a muddy hillside.

Chinese authorities have recovered the jet’s so-called black boxes, containing cockpit voice and flight data recorders and about 36,000 fragments of wreckage, so far. Some parts of the data recorder, which was recovered Sunday, were severely damaged, according to China’s regulators. That could complicate the task of retrieving and deciphering any information inside.

The fatal accident comes at a time of geopolitical tensions between the superpowers, and sensitivities are heightened because the companies involved include a state-owned airline and the largest U.S. exporter. Boeing has been working to resume deliveries of its 737 Max, a newer jet model, to China after a three-year halt sparked by a pair of fatal accidents that together killed 346 people.

(Updates with details of CFM involvement in second paragraph)

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