The pilots of the recently-crashed China Eastern Airlines flight failed to respond to calls from air-traffic controllers after tipping into a deadly nosedive. News organisation Bloomberg reported that the plane was travelling at close to the speed of sound just before it slammed into a hillside.

Such an impact may complicate investigators’ task because it can obliterate evidence and even damage data recorders designed to withstand most crashes.

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It is reported that the black boxes from Flight 5735 haven’t been recovered. Rough terrain and the state of the aircraft, which plunged from about 29,000 feet (8,840 metres), make the search difficult.

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According to data from Flightradar24, the Boeing Co. 737-800 was knifing through the air at more than 640 miles per hour, and at times may have exceeded 700 mph.

“The preliminary data indicate it was near the speed of sound,” said John Hansman, a Massachusetts Institute of Technology astronautics and aeronautics professor who reviewed Bloomberg’s calculation of the jet’s speed. “It was coming down steep.”

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Sound travels at 761 mph at sea level but slows with altitude as air temperature goes down and is about 663 mph at 35,000 feet.

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Investigators have offered no major insights as to why the Boeing Co. 737-800 jet carrying 132 people crashed near Wuzhou in southern China on Monday, saying at a press conference late Tuesday it was too early to draw clear conclusions about the cause.

All 123 passengers and nine crew are presumed dead.