An Air China jet that plunged 25,000ft in an emergency descent did so after a co-pilot mistakenly turned off air-conditioning systems in a bid to hide his e-cigarette smoke.
Citing anonymous industry sources, multiple Chinese state media outlets had reported earlier that, after the abrupt drop in altitude, the plane eventually climbed back to around 7,500 meters and flew to its destination with a less-than-adequate oxygen level in the cabin.
However, that was where things went wrong because he had accidentally switched off the air-conditioning unit instead, causing oxygen levels to lower and activating an altitude warning!
Chinese flight regulations prohibit all flight crew from smoking, and banned passengers from using e-cigarettes on board in 2006.
Oxygen masks were deployed during the descent on the flight from Hong Kong to the port city of Dalian in northwest China. Air China says it will "adopt a zero-tolerance attitude and seriously punish those found responsible", depending on the results of the CAAC's probe.
In 2015, government-run China National Radio said four passengers on an Air China flight from Hong Kong to Beijing smelled strong smoke coming from the cabin.
Hoby Sun, the passenger who provided CNN with the flight altitude data, said everyone was calm when the oxygen masks dropped.
It also seems odd that merely turning off the air conditioning system would cause the plane to plunge 25,000 feet.
Aviation experts were not entirely satisfied with the results of the preliminary investigation, pointing out that it was risky for the pilots to proceed with the rest of the flight after the passengers used up all of the bottled oxygen, leaving no reserves to deal with an actual in-flight emergency.
Reuters noted that while Chinese airlines have a good safety record overall, there have been previous passenger complaints about pilots furtively smoking.