A clumsy co-pilot caused an Air China plane to plunge almost 20,000 feet midair when he pulled the wrong switch while trying to shut off an air recycling system - so he could vape in the cockpit.
A co-pilot smoking an electronic cigarette in the cockpit of an Air China flight caused the plane to suddenly drop 6,000 meters when he mistakenly turned off its air conditioning system.
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.
Air China said it would terminate the contracts of the employees involved in the emergency descent incident, and suggested that the CAAC cancel their licences, it said on its official account on China's Weibo.
The regulator's safety officer Qiao Yibin said the crew had to perform emergency measures, dropping oxygen masks until they could figure out the problem.
After the sudden descent to 10,000 feet (approx 3,000 metres), the plane thankfully recovered when it managed to climb back to 26,000 feet (approx 7,900 metres) and ended up arriving safely in Dalian.
An investigation into the incident by the Civil Aviation Administration of China discovered that the first officer was trying to hide the fact that he had been smoking an e-cigarette in the cockpit from the flight's captain, the BBC reported.
Rapid loss of cabin pressurization can be deadly.
If a plane loses cabin pressure, it must fly at a lower altitude to give crew and passengers breathable air.
Hoby Sun, the passenger who provided CNN with the flight altitude data, said everyone was calm when the oxygen masks dropped.
"I'm not physically hurt, but the psychological impact lingers. When I close my eyes, I see the oxygen masks dangling in front of me", he told CNN.
Air China, headquartered in Beijing and a member of the Star Alliance global network, has a fleet of more than 600 planes.