A China Airlines Boeing 737-800, registration B-18609 performing flight CI-25 from Guam (Guam) to Taipei (Taiwan) with 109 passengers and 13 crew, was enroute at FL370 about 180nm northwest of Guam when the crew initiated an emergency descent due to the loss of cabin pressure, the passenger oxygen masks were released. The aircraft returned to Guam for a safe landing on runway 06R about 40 minutes later. There were no injuries and no damage to the aircraft.
The flight was cancelled.
A replacement Boeing 737-800 registration B-18656 reached Taipei the following morning with a delay of 13 hours.
Taiwan's ASC reported they have dispatched investigators to Guam to investigate the circumstances of the cabin pressure control exception resulting in the release of the passenger oxygen masks after the aircraft had climbed to FL370. The aircraft carried 109 passengers, 3 flight crew and 10 cabin crew. The occurrence was rated an accident.
On Jun 5th 2017 the ASC released their final report in Chinese and executive summary concluding the probable cause of the accident (maintaining the rating as accident) was:
Findings related to probable causes
- A gear pin of cabin pressure system outflow valve was broken so that the outflow valve could not be controlled which resulted in abnormal cabin pressure and air turned back to Guam.
Findings related to risk
- During the Operator's so-called “the contents of the Fault Isolation Manual is incomplete” event happened, the Aircraft On Ground team did not contact the Boeing for professional and effective recommendations. After the end of rescue, the team did not actively inquire about the cause of failure message during troubleshooting.
This indicates that the China Airlines should implement the execution of maintenance management rules.
The ASC reported that climbing through 27300 feet the crew received indications that the cabin pressure control AUTO and ALTN modes had failed, the crew switched to manual control, determined that the cabin pressure was controllable and continued the climb to FL370. After levelling off at FL370 the crew detected that the cabin altitude was still climbing at about 500 fpm, initiated an emergency descent to FL100 and returned to Guam.