A co-pilot who was smoking an e-cigarette is being investigated after his plane was forced to make an emergency descent when smoke entered the cabin.
The co-pilot aboard a domestic Air China flight from Hong Kong to Dalian on Tuesday plummeted 25,000 feet in 10 minutes.
According to the South China Morning Post, the Civil Aviation Administration of China (CAAC) has launched an investigation into the incident involving Air China flight CA106.
The CAAC has said there were no injuries to the 153 passengers and nine crew.
According to investigators, the co-pilot caused the plane to drop when he attempted to turn off the fan in a bid to stop the vape aerosol reaching the passenger cabin.
News of this incident began to circulate on Chinese social media as pictures of passengers wearing oxygen masks on the plane alarmed netizens.
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"Smoke diffused into the passenger cabin and relevant air conditioning components were wrongly shut off, without notifying the captain, which resulted in insufficient oxygen".
Qiao Yibin, an official of the regulator's aviation safety office, said the shut-off triggered an alarm, prompting the crew to perform an emergency pressure relief procedure, which then released the cabin's oxygen masks. Once the pilots saw the air conditioning was off, they turned it back on and regained altitude.
Instead, the wingman accidentally triggered a drop in oxygen levels, prompting an altitude warning that caused the almost fatal plunge - from 32,800 to 13,100 feet in less than nine minutes, Civil Aviation Administration of China officials told the station.
The CAAC said it had requested the aircraft's flight data and cockpit voice recorder as part of its probe.
"I didn't think too much of it at the time - we didn't know what was going on, nor did the flight attendants it seemed", he told CNN on Thursday.
China bars flight crews from "smoking on all phases of operation", and passengers there haven't been able to use e-cigarettes on planes since 2006.