E-cigarette triggers deployment of oxygen masks during flight from Hong Kong.
A vaping co-pilot forced a passenger plane to plummet 10,000ft after he triggered a drop in cabin oxygen levels, according to state media.
The Air China Boeing 737 was flying to the Chinese city of Dalian from Hong Kong when oxygen masks were suddenly deployed and it was forced into an emergency descent. China’s aviation regulator said the pilot was smoking an e-cigarette during the flight.
It eventually climbed again and continued to its destination, but not before fuelling the concerns of safety experts.
Chinese airlines have a good safety record in general, but passengers have, on occasion, accused pilots of smoking during flights. Few such incidents have ever been confirmed.
"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 Tuesday's incident.
"Smoke diffused into the passenger cabin and relevant air conditioning components were wrongly shut off, without notifying the captain, which resulted in insufficient oxygen," it quoted Qiao Yibin, an official of the regulator's aviation safety office, as saying.
China News added that the co-pilot had shut off the air conditioning units.
Mr Qiao said the shut-off triggered an alarm, prompting the crew to perform an emergency pressure relief procedure which released the cabin's oxygen masks.
The crew realised the problem after the descent and restored the air conditioning, allowing cabin pressure to return to normal, he added.
The CAAC said it was continuing the investigation and was analysing the aircraft's flight data recorder and cockpit voice recorder.
Air China did not immediately respond to requests for comment. It vowed a "zero tolerance" approach towards wrongdoing by any crew on its official account on China's Twitter-like Weibo on Wednesday.
The incident featured heavily on Chinese social media on Friday, with some commentators demanding harsh punishment and revocation of the pilot's flight license.
China's aviation regulations, which bar flight crew from "smoking on all phases of operation", also banned passengers from using e-cigarettes on flights in 2006.
Users of online airline forums have occasionally accused pilots of smoking during flights, however.
In 2015, government-run China National Radio said four passengers on an Air China flight from Hong Kong to Beijing smelt strong smoke coming from the cabin.
The following year, the US prohibited the use of e-cigarettes on commercial flights.