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.