Aviation Safety Council releases the investigation final report of China Airlines flight 781 Occurrence, involving emergency descent by excess cabin altitude warning triggered around 110 nautical miles north east from Ho Chi Minh city.
On June 3, 2013, an Airbus A330-300 airplane, registration number B-18317, operated by China Airlines (CAL) conducting a scheduled passenger flight CI781 from Taoyuan International Airport, Taiwan, for Tan Son Nhat International Airport in Ho Chi Minh, Vietnam. Due to No. 1 & No. 2 engine’s bleed system failure, triggered “EXCESS CABIN ALTITUDE” warning afterward and led the flight crew to make emergency descent by the emergency procedure. Two flight crewmembers, 13 cabin crewmembers, and 185 passengers, in total of 200 people were onboard. There was no damage to the aircraft and no injury to the occupants.
Approximate one minute after take-off, ECAM (Electronic Centralized Aircraft Monitoring) message “AIR ENG 2 BLEED FAULT” was displayed. After the flight crew reset No. 2 engine bleed system, and the engine bleed system was momentarily recovered, then the same system failure message was displayed again. One minute later after descent, ECAM message “AIR ENG 1 BLEED FAULT” was displayed. Flight crew deployed speed brake to expedite their descent, ECAM message “CAB PR EXCESS CAB ALT” was displayed. The flight crew donned oxygen masks in accordance with the procedure and announced “MAYDAY” to ATC. The aircraft leveled at 10,000 ft. The condition of cockpit and cabin were normal after flight crew’s inspection. The passenger oxygen masks did not drop. The “MAYDAY” call was cancelled by the flight crew and the aircraft resume normal descent. The aircraft arrived at Tan Son Nhat International Airport safely.
After being notified by Civil Aeronautics Administration and China Airlines on June 3, ASC had contact with Civil Aviation Authority of Vietnam (CAAV) immediately. In accordance with ICAO Annex13 paragraph 5.1, CAAV delegated ASC to be in charge of the investigation. The ATC recording and transcript of the occurrence were also provided by CAAV. ASC accepted the delegation and started investigation. Organizations and authorities were invited to participate in the investigation included: Civil Aeronautics Administrations, Ministry of Transportation and Communications, China Airlines, Bureau d'Enquêtes et d'Analyses pour la sécurité de l'aviation civile (BEA), Airbus. AAIB Singapore (Air Accident Investigation Bureau of Singapore) on behalf of ASC witnessed the test of faulty parts at LIEBHERR Singapore factory and presented their witness report. Investigation Report was published after approval by the ASC council members on October 29, 2013, at the 16th Council Meeting.
Findings related to probable causes: Harden and broken of No.1 Fan Air Valve Thermostat’s O-ring, internal contamination of No. 2 Fan Air Valve Thermostat, made the openings of No.1 Fan Air Valve and No. 2 Fan Air Valve reduced, engine bleed air temperature risen by insufficient cooling air , two engine’s bleed air Pressure Regulating Valves were closed due to engine bleed air over temperature, which caused two engine bleed systems to fail, triggered “EXCESS CABIN ALTITUDE” warning afterward and led the flight crew to make emergency descent by the emergency procedure.
There is no safety recommendation issued. Concerning organizations and authorities had implemented 22 preventive and corrective measures (details as Executive Summary) to the Findings during the Investigation.
The report in Chinese can be downloaded at http://www.asc.gov.tw
Contact: Sherry Liu, Engineer
TEL: +886-2-89127388 ext. 330