Beijing (CNN) A co-pilot smoking an electronic cigarette in the cockpit of an Air China flight caused the plane to suddenly drop 6,000 meters (19,600 feet) when he mistakenly turned off its air conditioning system.

A senior official from the Civil Aviation Administration of China (CAAC) told reporters Friday that, without notifying the pilot, the unnamed co-pilot was trying to turn off air recycling fans to prevent the vapor from spreading into the passenger cabin.

Instead, he toggled the wrong switches, which were close to his intended target, leading to a drop in oxygen levels that triggered altitude warnings.

Qiao Yibin, the CAAC official, promised to hand down "severe punishment in accordance with laws and regulations," if the regulator's final conclusion on the incident matches its initial finding.

Air China fired the entire flight deck crew and suggested CAAC revoke their pilot's licenses upon completing its investigation, the country's flag carrier said Friday night in a statement.

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