Incident Overview
On April 11, 2014, China Airlines flight CI7916, a Boeing 737-800 (registration B-18601), was cruising at an altitude of 35,854 feet near Bangkok when cabin crew heard a loud bang and detected an electrical burning odor. Passengers reported smoke emanating from the ceiling. A flight attendant observed a discolored area and black debris on the ceiling above the left forward passenger door, and felt an electric shock upon touching the panel. The purser deactivated the forward galley 2 power supply. Using a fire axe to enlarge a crack in the ceiling, the crew saw a 30 cm electrical arc and discharged fire extinguisher into the opening, stopping the arcing. The captain, after providing the axe, also saw the arc and decided to divert to Bangkok, where the aircraft landed safely with all 155 passengers and 8 crew members.
Aircraft and Flight Details
The aircraft was a Boeing 737-800 manufactured in 1998, with 16 years of service at the time of the incident. The flight was a scheduled passenger service from Yangon to Taipei. The investigation was conducted by the Taiwan Aviation Safety Council (ASC) under authorization from Thai authorities, with participation from the Civil Aeronautics Administration, China Airlines, Boeing, and the US National Transportation Safety Board.
Investigation Findings
The investigation determined that the forward galley 2 electrical wires were compressed against the right edge of the ceiling panel. Vibration during normal flight caused chafing, which wore through the wire insulation and the ceiling's conductive carbon fiber layer. This created a direct electrical contact between the bare wire and the carbon fiber, causing a short circuit when the left edge of the ceiling contacted a metal support beam. The short circuit resulted in smoke and arcing.
Two possible explanations were identified for the wire compression: 1. The wires were compressed against the ceiling since the aircraft's manufacture 16 years prior, but the issue was mitigated by a wrap that later became open during maintenance 8 years before the incident. 2. During maintenance 8 years prior, a wiring harness was reinstalled without proper alignment markings, causing the wire clips to be misplaced and creating the compression.
The investigation also noted that the airline's maintenance procedures lacked training on marking component positions before disassembly, and the work order did not include steps for such markings. Additionally, the cabin crew's understanding of emergency procedures varied, which could affect coordination.
Safety Actions
China Airlines had already implemented corrective measures before the report's publication:
- Enhanced training on wire clip installation and the consequences of improper alignment.
- Issued directives emphasizing the need for alignment markings and correct clip orientation.
- Replaced the paper job suggestion sheet system with an electronic system to ensure accurate records.
- Revised the Cabin Crew Safety and Emergency Procedures Quick Reference Manual to clarify the use of the manual and improve crew coordination.