AN investigation has been launched after an Air China jet plummeted over 20,000ft when smoke from a pilot's e-cigarette entered the cabin.
"In the preliminary investigation, the co-pilot was found to be smoking an e-cigarette", state-owned China News said, citing a news conference by the Civil Aviation Administration of China (CAAC) investigating the incident.
The CAAC official said the incident is being investigated and "severe punishment in accordance with laws and regulations" will be delivered if the investigation proves that the initial finding was the reason behind the incident.
Industry experts said the decision to climb and continue the flight was unusual given the oxygen masks had already been deployed.
Meanwhile, Air China added that if the pilot had indeed been smoking on the flight, they would deal with those responsible with "zero tolerance".
The aircraft, which was flying to the Chinese city of Dalian from Hong Kong, was carrying 153 passengers and nine crew members at the time.
The airline prohibits smoking, including e-cigarettes, on all its flights.
After the plane dropped to around 3,000 meters, the pilots realized the problem and switched the air-conditioning back on, before returning the aircraft to its cruising altitude and completing the journey to Dalian. 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.
Within a matter of 18 minutes, the plane was down to just 12,300 feet.
Per the South China Morning Post, a couple of the passengers posted pics and video on social media showing people donning the oxygen masks that came down, though the mood was relatively calm.
According to the outlet, the unnamed male co-pilot "tried to hide the fact that he was smoking" in the cockpit and attempted to turn off a fan to prevent smoke from reaching the passenger cabin "without telling the captain", but accidentally turned off the air-conditioning unit instead.