An emergency descent by anÂ-AirÂ-ChinaÂ-aircraft after cabin oxygen levels dropped has been linked to a co-pilot smoking an e-cigarette during the flight, state media said on Friday. The state-backedÂ-AirÂ-ChinaÂ-Boeing 737Â-aircraft was flying to the Chinese city of Dalian from Hong Kong when it went down to 10,000 feet (3,048 m), with oxygen masks deployed. Then it climbed again to continue to its destination, an incident that fuelled the concerns of safety experts. ChineseÂ-airlines have a good safety record in general, but passengers have, on occasion, accused pilots of smoking during flights. Few such incidents have been confirmed, however. "In the preliminary investigation, the co-pilot was found to be smoking an e-cigarette," state-ownedÂ-ChinaÂ-News said, citing a news conference by the Civil Aviation Administration ofÂ-ChinaÂ-(CAAC) investigating Tuesday's incident. "Smoke diffused into the passenger cabin and relevantÂ-airÂ-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. ChinaÂ-News added that the co-pilot had shut off theÂ-airÂ-conditioning units. Qiao said the shut-off triggered an alarm, prompting the crew to peform an emergency pressure relief procedure, which then released the cabin's oxygen masks. The crew realised the problem after the descent and restored theÂ-airÂ-conditioning, allowing cabin pressure to return to normal, he added. The CAAC said it was continuing the investigation and was analysing theÂ-aircraft's flight data recorder and cockpit voice recorder. AirÂ-ChinaÂ-did not immediately respond to requests for comment. It vowed a "zero tolerance" approach towards wrongdoing by any crew, on its official account onÂ-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 onlineÂ-airline forums have occasionally accused pilots of smoking during flights, however. In 2015, government-runÂ-ChinaÂ-National Radio said four passengers on anÂ-AirÂ-ChinaÂ-flight from Hong Kong to Beijing smelt strong smoke emitted from the cabin. In 2016, the United States prohibited the use of e-cigarettes on commercial flights.



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