By Agence France-Presse Chinese authorities have cut flag carrier Air China's 737 flights and revoked the flying licences of the cockpit crew involved in a mid-air emergency sparked by a co-pilot's vape smoke, state media said Wednesday. (AFP/MANILA BULLETIN) An Air China 737 made a rapid emergency descent last week after the co-pilot mistakenly turned off air-conditioning systems in a bid to conceal his e-cigarette smoke. The incident, which resulted in the deployment of passenger oxygen masks, occurred on a flight from Hong Kong to the northeastern city of Dalian. The Civil Aviation Administration of China (CAAC) has cut the carrier's 737 flights by 10 percent and ordered it to undertake a three-month safety overhaul, China Central Television (CCTV) said. The aviation watchdog also fined Air China 50,000 yuan ($7,500). Boeing 737s accounted for more than 40 percent of Air China's fleet as of the end of last year, company reports have shown. Air China shares slipped more than two percent in Shanghai on Wednesday morning following the punishment. The CAAC has said the drama was triggered when the co-pilot, trying to prevent his vape smoke from spreading into the main cabin, accidentally switched off the air conditioning. That led to a decrease in cabin oxygen levels which in turn set off an emergency warning system indicating the jet may have flown too high and instructing the pilots to quickly descend. Smoking is not allowed aboard Chinese commercial passenger flights. Chinese media reports quoted passengers and flight-tracker sites as saying the plane may have quickly descended as much as several thousand meters. There were no injuries to the 153 passengers and nine crew, the CAAC has said.