Pilot Debrief

BOEING 767-300F near Memphis, TN — 2023-10-18

Final reportENG24FA003
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Date
2023-10-18
Location
Memphis, TN, USA
Airport
MEM
Aircraft
BOEING 767-300F
Registration
N287FE
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Initial climb

Probable cause

A high-pressure fuel leak from a gap in the bolted flange interface between the main fuel pump’s fuel crossover supply tube and the hydromechanical unit idler adapter pad, which resulted in the crossover tube flange bolts partially pulling out and allowing fuel to escape and ignite on contact with the engine’s heatshield. Contributing to the fuel leak was Avio Aero's incorrect manufacture of the idler adapter pad bolt holes, which deviated from GE's manufacturing print requirement; Avio Aero's improper installation of threaded inserts into the idler adapter bolt holes; Avio Aero's failure to inform GE about the manufacturing deviation and request approval; and GE's failure to identify the manufacturing deviation during adapter quality and compliance design reviews.

Contributing factors

Contributing to the fuel leak was Avio Aero's incorrect manufacture of the idler adapter pad bolt holes, which deviated from GE's manufacturing print requirement; Avio Aero's improper installation of threaded inserts into the idler adapter bolt holes; Avio Aero's failure to inform GE about the manufacturing deviation and request approval; and GE's failure to identify the manufacturing deviation during adapter quality and compliance design reviews.

NTSB narrative

The incident engine, a General Electric (GE) CF6-80C2 turbofan, suffered an undercowl fire due to a high-pressure fuel leak originating from a bolted flange interface between a high-pressure fuel crossover tube and the hydromechanical unit (HMU) accessory gearbox adapter pad. The engine’s accessory heat shield surface temperatures and stagnant airflow near the fuel leak location were sufficient to cause ignition. Two threaded inserts in the adapter pad were found protruding and likely prevented the fuel tube from correctly seating on the adapter pad surface. Threaded inserts were not securely installed into the adapter pad, which allowed the crossover tube bolts to partially pull out. Multiple insert holes had stripped threads, linear scoring, counterclockwise material smearing, missing surface anodization, cross-threading, and concave hole profiles. Avio Aero, the adapter manufacturer, implemented an automated pre-tap operation that pre-machined threads into the adapter pad to ease installation of self-tapping steel inserts. In early 2023, this pre-tap operation was determined to be a deviation from the part’s drawing requirements. Neither GE Aerospace nor Avio Aero could find documentation supporting the decision to pre-tap the adapter holes or Avio Aero communicating to GE of their decision to deviate from the print requirement. Avio Aero may have decided to pre-tap the adapter holes because other parts were using this process.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Failure to ensure proper installation of threaded inserts during manufacturing.

NTSB coding

Evidence available

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

Docket documents10

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