The Aviation Safety Council (ASC) published an investigation report of a China Airlines B737-800 passengers flight diverted to Bangkok due to electric arc and smoke appeared in forward cabin ceiling. The forward galley 2 electric arc and smoke were caused by compression of the electric wire rubbing against the ceiling panel during vibration of normal operation, The conducting wire inside the electric wire and graphite fibers inside the ceiling panel was exposed due to the rubbing against each other, the conducting wire and the graphite fibers direct compression lead to short circuit between the left hand side of the panel and the metal beam, caused the cabin electric arcing. The aircraft had no damage and people on board were all safe.

According to the ROC Aviation Occurrence Investigation Act, and the content of Annex 13 to the Convention on International Civil Aviation (Chicago Convention), which is administered by the International Civil Aviation Organization (ICAO), the ASC, an independent agency of the ROC government responsible for civil aviation occurrences investigation. The occurrence was occurred in the territory of Thailand. After the power of the investigation was delegated by the director department of the Thailand Government the ASC commenced the investigation. The investigation team included members from operator, China Airlines, Civil Aeronautics Administration Taiwan and the state of manufacture, represented by NTSB (National Transport Safety Board, USA) including technical advisor from Boeing. The Investigation report was approved in the ASC 30th Board meeting on January 27, 2015.

Findings related to probable causes：

In total there are 2 findings:

• There were existing compression situation of forward galley 2 electric wire and the ceiling panel, the normal operation vibration caused the wire rubbing against the ceiling panel. The exposed conducting wire inside the electric wire and graphite fibers inside the ceiling panel rubbing against each other caused short circuit happened between the left side panel and the metal beam. The electric circuit from conducting wire to the right hand side then to the left hand side metal beam panel, the electric circuit formed a short circuit to ground and caused the cabin electric arcing.
• There are 2 probable causes regarding to the situation of the compression between the forward galley 2 electric wire and the ceiling panel.
  • When the aircraft was shop out 16 years ago, the forward galley 2 wire had compressed to the ceiling panel, however, the occurrence did not occur due to the wire wrap was the close type; 8 years ago, the wire wrap was changed to open type when the mechanic re-installed the clamp and wire in accordance with Engineering Order (EO) instruction, at the time the wire had compressed to the ceiling panel directly. The vibration of normal operation caused the electric wire to rubbing against the ceiling panel. The conducting wire inside the electric wire and graphite fibers inside the ceiling panel was exposed and compressed each other.
  • China Airlines did not train the mechanic regarding the positioning marking before remove and reinstall the components when the aircraft was shop out; consequently, the mechanic did not perform positioning marking when the EO was performed 8 years ago. The EO content also did not include the positioning marking step which caused the clamp was installed onto the fore side of the fastener mistakenly lead the wire compressed to the ceiling panel.

China Airlines proposed the improvement measures and safety actions been taken to ASC on November 28th, 2014 prior to ASC report publishing. The following ASC proposed safety recommendations to China Airlines are no longer needed.

• Educate avionics, cabins, general, etc departments maintenance personnel must perform the positioning marking procedure to identify the original composed positions whenever dismantle the components.
• Human factor risk shall be considered of all Maintenance Departments, add a warning instruction or note for the execution of the position marking before dismantling the components on the job cards in a proper manner.
• Maintenance Department shall preserve the correct maintenance records after the tasks and review the paper form work recommendation sheet procedure
• Review the SEP Cabin Quick Reference Handbook (CQR) using timing and manner to prevent important procedure missing , enhance crew cooperation during abnormal event happening..

The investigation report in Chinese can be download at ASC website: www.asc.gov.tw/downfile/ASC-AFR-15-03-001

Contact: Sherry Liu, Engineer

Tel: 89127388-330

Email: Sherry@asc.gov.tw