BEIJING — China Eastern Airlines Flight 5735 was at 29,100 feet in clear afternoon skies over the hills of southern China, seemingly ready for a smooth landing in Guangzhou. The plane, a Boeing 737-800 NG, was only seven years old. One of China’s most experienced aviators was among the three pilots in the cockpit.But then, at 2:20 p.m. on March 21, the aircraft plummeted.Air traffic controllers made frantic calls that went unanswered. The pilots sent no mayday messages. The plane fell more than 20,000 feet in less than a minute, to 7,400 feet. Then it gained 1,200 feet of altitude in about 15 seconds, before a final plunge into a hillside covered in bamboo groves and banana trees. The plane was …
