Pilot Debrief

BOEING 747 near Dallas, TX — 2013-02-25

Final reportENG13IA016
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Date
2013-02-25
Location
Dallas, TX, USA
Aircraft
BOEING 747
Registration
B18701
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Taxi

Probable cause

Fuel leaking from a fractured fuel manifold feeder line that ignited on contact with the engine’s hot compressor rear frame, which resulted in an engine undercowl fire. The fuel manifold feeder line failed due to high amplitude fatigue because the fuel manifold resonance frequencies were within the engine operation range. Contributing to the incident was that the engine was overhauled about the same time as the most current fuel manifold configuration that addressed the high amplitude fatigue failure mode was introduced, thus it was not installed on the engine.

Contributing factors

Contributing to the incident was that the engine was overhauled about the same time as the most current fuel manifold configuration that addressed the high amplitude fatigue failure mode was introduced, thus it was not installed on the engine.

NTSB narrative

On February 25, 2013, a Boeing B747-409F freighter, B-18701, powered by four General Electric CF6-80C2B1F turbofan engines, experienced a No. 2 (left inboard) engine undercowl fire while taxiing after landing at Dallas/Fort Worth International Airport, Dallas Texas. After receiving the fire warning, the pilots discharged a fire suppression bottle and the fire ceased. There were no injuries to the three crewmembers on board and no airplane damage was reported. The incident flight was a regularly scheduled cargo flight, operated by China Airlines under provisions of 14 Code of Federal Regulations Part 129, from Taipei, Taiwan, to Dallas with stops in Anchorage, Alaska, and Atlanta, Georgia. Initial visual examination of the engine found that at the No. 2 fuel nozzle position, the right fuel manifold feeder tube aft o-ring support was displaced rearward against the snap ring. When the No. 2 fuel nozzle feeder tube shroud was removed, the feeder tube was found fractured and separated between the feeder tube-to-ferrule weld joint and the aft o-ring, which is one of the features that prevents a fuel leak when the feeder tube fractures. Metallurgical examination revealed that the feeder tube fractured due to lower alternating stress high-cycle fatigue cracking that transitioned to increasing alternating stress fatigue cracking before ultimately failing in overload. Further, the o-ring had sustained a spiral-like separation. Additional examination confirmed that no inclusions or any material anomalies at the feeder tube crack initiation sites and that the material properties of the feeder tube and o-ring and the weld quality met their required specifications. The fracture mode of the feeder tube is well-documented and GE issued Service Bulletin (SB) 73-0371 to introduce a redesigned fuel manifold and bracket to address this issue. Service Bulletin 73-0371 also introduced changes to the manifold feeder tube configuration and orientation (to avoid resonance frequencies of the manifold that were within the engine operating range) to prevent fuel manifold fractures and wear-through of the tube thickness that had resulted in previous fuel leaks and undercowl fires. The SB was issued just 7 days before the installation of the incident fuel manifold on the incident engine; therefore the operator was unable to install the most current fuel manifold design.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Failure to incorporate updated fuel manifold configuration before installation.

NTSB coding

  • Fire/smoke (non-impact) · Taxi-from runway

Evidence available

  • FDR / data
  • Photos
  • 10 docket documents
View NTSB final reportView NTSB docket

Docket documents10

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