What happened
On April 11, 2014, China Airlines flight CI 7916, a Boeing 737-800 with registration B-18601, was operating a passenger service from Yangon to Taipei. While cruising at approximately 36,000 feet, about 500 kilometers northwest of Bangkok, a flight attendant heard an explosion-like sound and noticed a burnt smell. Passengers also reported seeing smoke emanating from the cabin ceiling.
Upon inspection, the crew found a charred area and black residue on the ceiling near the forward left boarding door. The flight attendant reported feeling a slight electric shock when touching the panel, prompting the purser to immediately shut off the power to the Forward Galley 2 (FG2) equipment. To investigate a potential hidden fire source, the crew used an axe to enlarge a small hole in the ceiling. During this process, a 3-cm electrical arc burst from the crack. The crew applied fire extinguishing agent into the opening, which eventually suppressed the arcing. The flight crew subsequently decided to divert the aircraft to Bangkok, where all 155 passengers and 8 crew members landed safely.
The investigation
The Taiwan Transportation Safety Board (TTSB) investigated the incident, which took place in Thai airspace. The investigation focused on the physical cause of the electrical arcing and the maintenance history of the aircraft. Investigators examined the wiring in the Forward Galley 2 area and found that the electrical wiring was being compressed against the ceiling edge.
Detailed inspection revealed that the insulation on the wires had been worn away, exposing the conductors. The friction caused by aircraft vibrations led to the exposed wires making contact with the conductive carbon fiber cloth of the ceiling. This created a short circuit path from the right side of the ceiling to the metal support beam on the left side. The investigation also looked into whether the wiring configuration was incorrectly installed during previous maintenance work performed eight years prior.
Findings
- The primary cause of the smoke and arcing was a short circuit resulting from the compression of electrical wiring against the ceiling edge.
- Continuous vibration during normal operations caused the wire insulation to degrade and the ceiling coating to peel, exposing the conductive carbon fiber cloth.
- The investigation identified two possible scenarios for the wiring compression: either the compression existed since the aircraft's manufacture but was previously mitigated by a protective sleeve that was removed during a recent maintenance update, or maintenance personnel incorrectly reinstalled the wire clamps during a previous engineering order without proper positional markings.
- Discrepancies were noted in maintenance records, where some inspection photographs did not match the written logs regarding wire contact with the ceiling or ground wires.