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.
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.
Boeing 767-300F · N287FE — 245,448 samples, 14 parameters, 44:28:20.0 to 47:43:19.8.
| Time | Event | Page |
|---|---|---|
| 15:36:10 | Recorded fuel pressure values from the left engine started to decrease, with no corresponding change in throttle resolver angle | 5 |
| 15:37:49 | The left engine had a fire indication, and simultaneously a master warning occurred | 5 |
| 15:38:25 | Flight data recorder lost synchronization, likely due to a momentary power loss, for less than one second | 4 |
| 15:39:09 | Data indicated that fuel had been cut off from the left engine | 5 |
| 15:39:26 | FIRE EXT SWITCH L indicated PULLED | 5 |
| 15:42:00 | Left engine no longer had a fire indication | 5 |
| 15:43:09 | Flight data recorder lost synchronization, likely due to a momentary power loss, for less than one second | 4 |
| 15:49:00 | The airplane landed at MEM without further incident | 5 |
Docket: data.ntsb.gov/Docket/?NTSBNumber=ENG24FA003. This brief is an analytical aid assembled from public records; it is not an investigative finding.