An Air China Boeing 737-800, registration B-5851 performing flight CA-106 from Hong Kong to Dalian (China), was climbing through 10,700 meters (about FL350) about 40nm southwest of Shantou when the aircraft initiated an emergency descent due to the loss of cabin pressure, the passenger oxygen masks were released. Shortly after levelling off at 3100 meters (FL100) the crew climbed the aircraft to 7500 meters (FL246) and continued the flight to Dalian further stepclimbing to 8100 meters (FL266). The aircraft landed safely in Dalian about 3 hours after leaving 10,700 meters.
The airline reported both pilots were placed under investigation for suspicions of having been smoking on the flight deck which ultimately resulted in the cabin pressure problem and emergency descent. The airline will exercise zero tolerance should the crew be found guilty of such wrong doing.
The airline alleges that while smoking in the cockpit the crew mistakenly shut down both bleed air supplies causing the cabin to lose pressure. Believing the cabin pressure could not be controlled the crew thus initiated an emergency descent. After levelling off at safe altitude high temperatures in the cabin, as result of air just being recirculated, prompted the crew to further checks, the crew found both bleed air systems switched off, reactivated both bleed air systems which caused the cabin to pressurize again, the crew climbed the aircraft to 7500 meters and continued to Dalian.
Passengers posted photos and videos on China's Weibo service showing the passenger oxygen masks were released and automated announcements in Chinese and English occurred indicating the aircraft was performing an emergency descent and instructing the passenger of how to don their oxygen masks.
On Jul 13th 2018 the airline announced, that following investigation and verification the airline decided to make a "cessation of flight qualifications" effectively grounding both flight crew and terminate their labour contracts according to law. It has been recommended to China's Civil Aviation Authority CAAC to revoke the pilot licenses for both flight crew following the completion of the investigation.
China's Civil Aviation Authority had previously reported in a press conference that preliminary investigation results suggested the first officer was using electronic cigarettes. In an attempt to prevent smoke entering the cabin the first officer intended to shut down the cabin re-circulation fan without informing the captain, however, inadvertently shut down the bleed air instead which resulted in the cabin altitude alert and subsequent emergency descent. Only at 3000 meters the crew discovered the bleed air was switched off, re-engaged the bleed air and continued to Dalian.
Chinese Aviation Circles are also discussing the flight trajectories of a private aircraft and CA-106 in an obviously developing conflict, the private aircraft descended and maneouvered obviously in an evasive maneouver before returning to initial altitude and flight path.