Air China will fire pilots of an aircraft that plummeted 25,000 feet in 10 minutes, after the state aviation regulator said that one of them had smoked an e-cigarette and made an error that forced the plane’s emergency descent on Tuesday.

“After an investigation to verify the incident, the decision is to suspend the related crew from flying and terminate the contracts in accordance with the law. The crew members who are responsible for the incident have been seriously dealt with,” the airline said on Friday night.

Its statement, issued on the Chinese microblogging site Weibo, also recommended that the Civil Aviation Administration of China (CAAC) revoke the pilots’ licences after completing their own investigations.

The CAAC earlier said it had launched a full investigation into the incident involving flight CA106, which left Hong Kong International Airport on Tuesday evening for Dalian, carrying 153 passengers and nine crew members.

Half an hour later, oxygen masks dropped from the ceiling, and the plane descended to 10,000 feet as it was travelling between Shantou and Xiamen. The Boeing 737 later climbed back to 26,000 feet and arrived safely at its destination. No injuries were reported, and the aircraft was not damaged.

CAAC, which seized the aircraft’s flight data and voice recorders and interviewed crew members, said preliminary investigations found that the co-pilot had, without telling the pilot, tried to turn off a circulation fan to prevent e-cigarette smoke from reaching the cabin.

“[But the co-pilot] mistakenly switched off the air-conditioning unit that was next to it, resulting in insufficient oxygen in the cabin and an altitude warning,” said Qiao Yibin, of the authority’s safety office, at a press briefing on Friday, according to the state-run Xinhua news agency.

Air China’s website says smoking is strictly prohibited on all its flights. It is clearly stated that e-cigarettes are also banned.

On Friday, the airline said it had immediately launched an investigation into the incident and checked on “weak links” to rectify safety measures across the company. It expressed its appreciation for passengers and said it would “conscientiously” learn lessons from the episode to improve its safety management system and ensure such incidents did not recur.

Reacting to Air China’s statement, Will Horton, a Hong Kong-based analyst for the CAPA Centre for Aviation, said on Twitter that it was a “big showing” from the airline.

Still, “firing those involved and suggesting licence revoking quells the public but doesn’t address underlying problem(s),” he added.

Aviation experts also questioned the pilots’ decision to continue with the journey despite having used up emergency oxygen supplies after the sudden descent.

David Newbery, president of the Hong Kong Airline Pilots Association and a Cathay Pacific Airways pilot, said: “If the oxygen masks had been deployed, it would be foolhardy to [continue flying] because there would be no oxygen left in the event of a subsequent depressurisation.”

Geoffrey Thomas, editor-in-chief of the AirlineRatings website, which produces an annual air safety ranking, said: “China and Chinese airlines are now rated among the safest in the world, with an excellent safety record in recent times. Hopefully airlines and crews will learn from this incident.”

Following the mid-flight drama, the four year-old plane registered as B-5851 was flown without passengers to Beijing on Wednesday night and has not been used for any flights since, according to tracking website FlightRadar24.

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