A plane of Air China. (File photo: VCG)

Air China has fired the entire crew of a flight that plunged about 7620 meters because the co-pilot was surreptitiously vaping in the cockpit.

The incident occurred Tuesday on flight CA106 from Hong Kong to Dalian, a Civil Aviation Administration of China (CAAC) official said in a news briefing on Friday.

According to investigations, the co-pilot, without telling the pilot, attempted to turn off a circulation fan to prevent smoke from his electronic cigarette from reaching the cabin.

However, the co-pilot mistakenly switched off the air conditioning unit that was next to it, resulting in insufficient oxygen in the cabin and an altitude warning.

The plane plummeted to an altitude of 3,000 meters over Guangdong before recovering to an altitude of 8 kilometers, and arrived safely at its destination.

The plane carried 153 passengers and nine crew members. There were no injuries.

In addition to firing the crew, Air China suspended their flight qualifications, and seriously dealt with related managerial staff, according to the airline’s statement on Friday.

Air China said that it would learn from the mistake, stick to the principle of safety first, and maintain a zero-tolerance attitude toward safety violations.