The Aviation Safety Council (ASC) releases final report on investigation of a China Airlines flight CI025, air turn-back due to abnormal cabin pressure at approximately 150 nautical miles northwest of the Guam. 

On April 17, 2016, a China Airlines Boeing 737-800 aircraft, registration number B-18609, took off from Guam International Airport (Guam Airport) to Taoyuan International Airport to execute a schedule transportation flight. There were 3 flight crews, 10 cabin crews and 109 passengers, total 122 people on board. While this aircraft was leveled at flight level 370, the pressurization system malfunction and the cabin pressure went out of control. The flight crew requested air turn-back to Guam Airport.

In accordance with the Aviation Occurrence Investigation Act, Republic of China (R.O.C) and the content of Annex 13 to the Convention on International Civil Aviation Organization, the Aviation Safety Council, an independent agency of the ROC government is responsible for the occurrence investigation. The organizations or agencies been invited to join the investigation team included: National Transportation Safety Board (NTSB, USA), The Boeing Company, Civil Aeronautics Administration of Ministry of Transportation, and China Airlines.

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 the risks: 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.

Safety Recommendations

To China Airlines:

1. Enhance the training and evaluation program for maintenance personnel to be familiar with using Fault Isolation Manual. Require maintenance personnel following the procedures of Fault Isolation Manual when performing troubleshooting. If any doubt arises about Fault Isolation Manual was incomplete, consult manufacturer for advises. When encountering maintenance difficulty during troubleshooting, maintenance personnel shall be proactive to figure out and clarify the fault messages generated during troubleshooting to assure implementation of the maintenance management rules.
2. Enhance the training and assessment to the maintenance personnel on Technical Log Book entry to ensure the aircraft Technical Log Book must be logged with the referred section per Fault Isolation Manual accordingly during troubleshooting.

To Civil Aeronautics Administration:

1. Require transport category operators to enhance the training and evaluation program for maintenance personnel to be familiar with using Fault Isolation Manual. Require maintenance personnel following the procedures of Fault Isolation Manual when performing troubleshooting. If any doubt arises about Fault Isolation Manual was incomplete, consult manufacturer for advises.
2. Enhance inspection of the entry of the Technical Log Book of national aircraft to ensure that the troubleshooting procedure is performed in accordance with the Fault Isolation Manual.

Full investigation report is available for download at http://www.asc.gov.tw

Sherry Liu, Engineer
Tel: 89127388-330
Email:sherry@asc.gov.tw