Incident Description
On February 25, 2013, a China Airlines Boeing B747-409F freighter, registration B-18701, operating flight CI-5254, experienced a fire in the No. 2 (left inboard) engine cowl while taxiing after landing at Dallas/Fort Worth International Airport in Dallas, Texas. The aircraft was powered by four General Electric CF6-80C2B1F turbofan engines. After receiving a fire warning, the flight crew performed the Quick Reference Handbook (QRH) fire emergency check list and discharged a fire suppression bottle. The fire warning ceased after the bottle was discharged. The three crew members on board were not injured, and no airplane damage was reported. The incident flight was a regularly scheduled cargo flight operated under Title 14 CFR Part 129, originating from Taipei, Taiwan, with stops in Anchorage, Alaska, and Atlanta, Georgia, before arriving in Dallas.
Engine Inspection
Post-event inspection by China Airlines maintenance personnel, while the engine was still installed, confirmed sooting and thermal distress on the right-hand side of the No. 2 engine. A wet-motor test revealed fuel spraying near the No. 3 fuel nozzle fuel manifold shroud position. The engine was subsequently removed for internal borescope inspection, which found no anomalies or internal damage. Visual examination showed localized soot circumferentially from the 12:00 to 3:00 o'clock position and lengthwise from the fuel manifold aft to the high pressure turbine active clearance control manifold. The heaviest sooting was observed on the compressor rear frame aft of the right-hand fuel manifold, between the No. 2 and 5 fuel nozzle positions. Some electrical bundles and cushion clamps in the fire/soot area exhibited thermal distress. Fire detection loops were intact, but loop isolators from the 1:00 to 2:00 o'clock position behind the Nos. 3–5 fuel nozzle positions showed thermal distress and oxidation.
Initial examination of the right-hand fuel manifold revealed all hardware present and intact. The only anomaly was at the No. 2 fuel nozzle position, where the feeder tube aft o-ring support was displaced rearward against the snap ring. When the No. 2 fuel shroud was slid aft, the aft o-ring was found separated and the feeder tube was fractured at the weld joint forward of the aft o-ring support. The forward o-ring, attachment nut, and lock wire were present and in good condition. No other feeder tubes were fractured. Secondary anomalies included a separated but good condition aft o-ring for the No. 4 fuel shroud and a thermally distressed, flattened aft o-ring for the No. 5 fuel shroud.
Metallurgical Findings
Metallurgical examination of the separated ferrule portion of the No. 2 feeder tube found a 360° circumferential fracture adjacent to the rear weld toe. Multiple crack origins were located on the outer diameter at one localized area, with cracks propagating inward and circumferentially. The fracture features indicated initial propagation consistent with lower alternating stress high cycle fatigue (HCF), transitioning to increasing alternating stress fatigue. No inclusions or material anomalies were noted. The aft o-ring had a spiral-like separation but was fully present. Evaluation of the ferrule weld, fuel manifold composition, and o-rings confirmed they met specifications. The No. 2 fuel shroud exhibited two sets of circumferential wear marks on its inner diameter: one at the normal feeder tube location and one fully aft at the snap ring location. GE concluded that the aft wear/fretting pattern was created after the feeder tube fractured, as fuel pressure forced the fractured tube against the snap ring, and that the o-ring initially held fuel within the shroud before eventually failing.
Previous Events and Corrective Actions
The source noted four undercowl fires from fuel manifold leaks since GE introduced the drainless fuel manifold in August 1996, including this event. Previous events involved an Atlas Air Boeing 747-400F in 2002, a Skymark Boeing 767 in 2005, and an Air New Zealand Boeing 767 in 2006. In each case, fuel manifold feeder line fractures or wear led to fuel leaks and fires. GE issued service bulletins (SB) to address these issues, including SB 73-0337 (C-shaped snap ring), SB 73-0365 (PTFE tape under clamps), and SB 73-0371 (new fuel manifold configuration with brazed clamps and modified feeder tube orientation). The event engine had all required SBs incorporated except SB 73-0371, which was released only seven days before the fuel manifold was installed. Following this incident, GE revised SB 73-0371 to accelerate compliance (Category 3) and allow on-wing incorporation.