Incident Overview
On March 31, 2022, at 19:05 UTC, a Bombardier Global 7500 business jet, registration 9H-VIG, powered by two General Electric Aviation Passport 20-19BB1A turbofan engines and operated by Vistajet, experienced a right (No. 2) engine fire during the takeoff climb from King Khalid International Airport in Riyadh, Saudi Arabia. After the right engine fire warning annunciated, the pilots disengaged the autothrottles and retarded the right engine throttle to idle. The fire warning ceased when the throttle was reduced. When the pilots incrementally increased the right throttle, the fire warning annunciated again. The crew then shut down the right engine, performed an in-flight air turn back to OERK, and made an uneventful landing with no injuries reported.
Post-Landing Inspection
Post-landing inspection of the right engine by GE on-wing support revealed indications of an undercowl fire and potential fuel leak locations. The engine was shipped to GE Cincinnati for evaluation. At fuel nozzle locations Nos. 12, 14, 16, and 18, the fuel manifold b-nut connections appeared shiny and lacked sooting, suggesting possible leak locations. A leak check using nitrogen at pressures well below normal and takeoff operational fuel pressures was attempted but no leak was produced. A torque check of all fuel nozzle-to-fuel manifold b-nut connections found that five had very low torque values (less than 200 inch-pounds) compared to the required installation torque of 285 inch-pounds nominal. One of these low torque locations was fuel nozzle No. 18. All other connections were within expected range.
Fuel Nozzle and Manifold Findings
After loosening all fuel manifold b-nuts, an attempt to retighten them by hand revealed that several b-nuts on the left fuel manifold could not be run down using normal force. Loosening the fuel nozzle attachment bolts at those locations enabled the b-nuts to be retightened freely by hand, indicating slight misalignment between the fuel nozzle and the fuel manifold. Fuel nozzle No. 18 male bullnose sealing surface exhibited galling along with elliptical and intermediate contact marks, indicative of misalignment contact with the fuel manifold female ferrule sealing surface. There were also signs of contaminants (hard particles) in the form of craters, indentations, and imbedded material on the sealing surface, along with diagonally orientated abrasive material marks consistent with previous repair. According to GE, there was no record of a repair operation on this specific nozzle at the fuel nozzle manufacturer or at the engine assembly site; GE concluded that this possible repair may have occurred sometime during engine assembly. The engine manual does not allow nicks or scratches but does allow blending; however, blending is only allowed in the circumferential direction for conical/cylindrical parts. The observed abrasive material removal marks on the No. 18 nozzle were in the diagonal direction along the axis of the part, inconsistent with manual instructions.
Only fuel nozzle No. 18 showed evidence of rework/repair; however, hard particle damage was also observed on the male bullnose seal surfaces of fuel nozzles Nos. 12, 13, and 16. GE was unable to confirm the source of the contaminants.
Additional Engines and Testing
During the investigation into the Riyadh and a similar Palm Beach event, two additional engines were found to have fuel manifold b-nut connection leaks during inspections performed by Bombardier. These two engines did not show evidence of an undercowl fire. GE performed leak, torque, and alignment checks on all engines along with visual examinations of sealing surfaces. Additionally, GE conducted acceptance test procedure engine runs, developmental engine runs, and component static rig tests to: understand effects of fuel nozzle-to-fuel manifold misalignment, gather assembly and operational loads/stresses on fuel manifolds under various installation scenarios, validate and develop installation best practices, gather torque relaxation data, and develop methods to minimize relaxation.
Contributing Factors
Based on data from the event engines, test engines, and component rig tests, several cumulative factors were found to have contributed to the fuel manifold leaks. Fuel manifold pigtail and fuel nozzle dimensional variation, combined with a given assembly sequence, can create potential misalignment between sealing surfaces, resulting in high thread resistance, low effective clamping force, and false high torque readings. This low effective clamped connection can relax/loosen during engine operation as the manifold geometry normalizes and the connection shifts. All leaking b-nut connections were found with lower than expected torque values. Since no fuel leaks occurred during development engine tests, and leaks could be induced and stopped with slight torque variations in component rig tests, GE concluded that multiple factors can be present to create a leak: false low torques due to misalignment, higher than anticipated assembly loads due to dimensional variation, and poor/distressed sealing surface condition.
Corrective Actions
GE and the Federal Aviation Administration took several corrective actions. GE issued service bulletins to borescope the engine compartment for signs of undercowl fuel leak or fire damage (72-00-0141-00A-930A-D-001) and to retorque fuel manifold b-nut connections (72-00-0142-00A-930A-D-001). The FAA issued Airworthiness Directive AD 2022-13-12 requiring visual inspection of the core compartment, retorque of coupling nuts, a ground power assurance check, and a follow-up borescope inspection. GE reviewed and changed fuel manifold and fuel nozzle installation and assembly procedures to provide more specific guidance, eliminate ambiguities, minimize misalignments, and incorporate feedback from assembly mechanics. GE also issued a “change in design” to finalize the optimum installation and assembly procedure using best practices developed during testing.