BEIJING—U.S. accident investigators arrived in China on Saturday to help authorities look for clues into what caused last month’s crash of a Boeing jetliner with 132 people aboard. The seven-member team from the National Transportation Safety Board will participate in the Civil Aviation Administration of China’s investigation of the March 21 crash of a China Eastern Airlines Boeing 737-800 because the aircraft was manufactured in the United States. As part of that assistance, the plane’s cockpit voice recorder is being downloaded and analyzed at a U.S. lab in Washington, federal officials said Friday. Investigators hope the recording will explain why the plane went into a nosedive from about 8,800 meters (29,000 feet) over a mountainous region in southeastern China. Chinese officials have said that air traffic controllers were unable to get a response from the pilots while the plane was descending. The cockpit voice recorder would pick up voices and other sounds from microphones …