“Given that two accidents both involved newly delivered Boeing 737-8 planes and happened during take-off phase, they have some degree of similarity,” the Civil Aviation Administration of China said Monday, emphasizing its principle of zero-tolerance on any safety hazards.

All Chinese domestic airlines were requested to suspend operation of the 737-8s by 6:00pm local time (10:00am GMT) and, according to local media and flight tracking resources, on most routes the jet has already been replaced with older-generation planes. 

Chinese carriers account for about 20 percent of the plane’s sales, with dozens of Boeing 737 MAX 8 jets already in operation and many more scheduled for delivery. China Southern Airlines Co. has the biggest fleet, with 16 of the aircraft, while Air China Ltd. currently operates 14 jets. China Eastern Airlines Corp. has 13.

With the first 737 MAX crash in late October still under investigation, this second tragedy might well have been a coincidence, but security concerns and the potential grounding of the entire MAX fleet would severely impact Boeing’s business. A Boeing spokesman declined Reuters’ request for a comment.

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