Incident
On October 18, 2023, at about 16:15 Central Standard Time, a FedEx Boeing 767-300F, registration N287FE, experienced a No. 1 (left) engine fire during initial climb from Memphis International Airport, Memphis, Tennessee. The aircraft landed safely. Airport rescue and firefighting observed damage to the No. 1 engine thrust reverser and core cowling but found no active fire, and no fire suppressant was applied. Ground inspection with the cowls and thrust reverser opened revealed the engine had sustained an undercowl fire.
Investigation Findings
The main fuel pump’s fuel inlet flange was found fractured while still bolted to the engine’s main fuel supply line. The exposed fracture surface appeared melted. Fractographic analysis confirmed melting and resolidification with no evidence of a mechanical failure mode.
A small area of coking was found on the hydromechanical unit’s idler adapter pad sealing surface where an upper fuel crossover tube attaches. This crossover tube delivers high-pressure fuel from the main fuel pump to the hydromechanical unit and is secured by four bolts installed into threaded steel inserts within the idler adapter. Two of these threaded inserts were found protruding or pulled out from the adapter pad.
Computed tomography scans revealed that three of the four idler adapter bolt holes used to secure the upper fuel crossover tube’s steel inserts had damaged or missing threads. The damaged bolt holes did not provide sufficient thread engagement to secure the crossover tube. High-pressure fuel loads likely caused the inserts to partially pull out, resulting in a gap between the crossover tube and the adapter pad.
Manufacturing Issues
Review of the idler adapter’s manufacturing requirements indicated that bolt holes should be drilled through and then have self-tapping threaded steel inserts installed. However, the incident adapter’s holes were drilled through and pre-tapped before inserting the steel inserts. Multiple insert holes exhibited stripped threads, linear scoring, counterclockwise material smearing, missing surface anodization, cross-threading, and concave hole profiles—evidence of improperly installed steel inserts into adapter holes with preexisting threads.
Avio Aero initially manufactured the hydromechanical unit idler adapter at its Brindisi, Italy facility in 1996 and moved production to its Turin, Italy facility in 2003. According to GE, the idler adapter should have completed a first article inspection at the Brindisi facility in 1996 and again at the Turin facility in 2003; however, no first article inspection documentation from either facility was found.
In early 2023, Avio Aero realized they were pre-tapping other non-GE parts that used self-tapping inserts, which deviated from drawing requirements. The idler adapter was identified as one such part, and Avio Aero removed the pre-tap operation from its manufacturing process in August 2023. Avio Aero then notified GE, who determined pre-tapped adapter holes violated the adapter drawing requirements. Avio Aero could not produce documentation showing who authorized the deviation or why the pre-tap operation was incorporated.
Corrective Actions
As a result of this investigation, GE Aerospace released Service Bulletin 72-1648 on June 28, 2024, requiring repetitive on-wing shim checks at each insert location and a one-time pull check of installed inserts at the next engine shop visit. The FAA was determining the need to issue an Airworthiness Directive mandating compliance with the service bulletin at the time of this report.
Avio Aero now uses a pneumatic tool to install the adapter’s threaded inserts and added an insert pull-out check to the manufacturing process. GE Aerospace plans to add notes to the next revision of the adapter drawing specifying no prior hole tapping is allowed, pull-out tests must be performed on all installed inserts, and installed inserts must not protrude above the surface.