9H-VIG

On March 31, 2022, at 19:05 universal coordinate time (UTC), a Bombardier Global 7500 Business Jet, registration number 9H-VIG, powered by two General Electric (GE) Aviation Passport 20-19BB1A turbofan engine and operated by Vistajet, experienced a right (No. 2) engine fire during the takeoff climb from the King Khalid International Airport, Riyadh, Kingdom of Saudi Arabia (OERK). After the right engine fire warning annunciated, the pilots disengaged the autothrottles and retarded the right engine throttle to idle. When the right engine throttle was reduced, the fire warning annunciation ceased. With the fire warning annunciation out, the pilots incrementally increased the right throttle and the fire warning annunciated again. The pilots shutdown the right engine, performed an in-flight air turn back to OERK, and made an uneventful landing with no injuries reported.

Post-landing inspection of the right engine by GE on-wing support in the Kingdom of Saudi Arabia revealed indications of an undercowl fire and potential fuel leak locations (Photo 1 and 2).

Photo 1: Sooting Damage

Photo courtesy of GE

Photo 2: Fuel Manifold B-nut Wetted at Top of Engine – Possible Leak Source

Photo courtesy of GE

The Kingdom of Saudi Arabia Aviation Investigation Bureau (AIB) informed the NTSB of this event on April 14, 2022, and the investigation was ultimately delegated to the NTSB. Due to the similarities with an on-going NTSB investigation (ENG22LA020), a joint Powerplant Group Chair Factual Report was created to document the findings for these two events.

The engine has 18 fuel nozzles and fuel is provided to the fuel nozzles by two fuel manifolds mounted on the outside of the combustion case (Figure 1).

Figure 1: Fuel Nozzle and Fuel Manifold Diagram

Figure courtesy of GE (modified by NTSB)

The engine was shipped back to GE Cincinnati to be evaluated. At fuel nozzle locations Nos. 12, 14, 16, and 18, the fuel manifold b-nut connections appeared shiny and lacked sooting and were thought to be possible leak locations. A leak check using nitrogen at pressures well below normal and takeoff operational engine fuel pressures was attempted but no leak was produced in the fuel system. A torque check of all the fuel nozzle-to-fuel manifold b-nut connects found that five had very low torque values, less than 200 inch-pounds, when compared to the other b-nut connection locations and the required installation torque of 285 inch-pounds nominal. One of the five low torque locations was fuel nozzle No. 18. All the other fuel manifold b-nut connection torque values were within the expected ranged.

After all the fuel manifold b-nuts were loosened, an attempt was made to retighten them by hand. Several fuel manifold b-nuts on the left fuel manifold could not be run down using normal force. Loosening of the fuel nozzle attachment bolts at those locations enabled the fuel manifold b-nuts to be retightened freely by hand onto the fuel nozzle threads. This was indicative of a slight misalignment between the fuel nozzle and the fuel manifold.

Fuel nozzle No. 18 male bullnose sealing surface exhibited galling along with and 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) on the fuel nozzle male bullnose sealing surface in the form of craters, indentations, and imbedded material on the sealing surface, along with diagonally orientated abrasive material marks/material removal consistent with what appears to be previous repair (Photo 3). According to GE, there was no record of a repair operation being performed on this specific nozzle at the fuel nozzle manufacturer or at the engine assembly site which would account for the observed abrasive material removal; therefore, GE concluded that this possible repair may have occurred sometime during engine assembly. The engine manual does not allow for any nicks or scratches but does allow for blending. However, blending is only allowed in the circumferential direction for conical/cylindrical parts; the blend/abrasive material removal marks on fuel nozzle No. 18 male bullnose sealing surface were in the diagonal direction along the axis of the part. Therefore, the observed blending in the area would be inconsistent with the engine manual blending instructions.

Photo 3: No. 18 FN Male Bullnose with Abrasive Marks and Particle Impression

Photo courtesy of GE (modified by NTSB)

Only the fuel nozzle No. 18 male bullnose sealing surface 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 (Photo 4). GE was unable to confirm the source of the contaminates.

Photo 4: High Magnification of Similar Shaped Debris Damage on Fuel Nozzle Male Bullnose Sealing Surface on Nos. 13 and 16

Photo courtesy of GE (modified by NTSB)

During the investigation into the Palm Beach and Riyadh fuel manifold leaks event, two additional engines were found to have fuel manifold b-nut connection leaks; those were discovered during inspections performed by Bombardier in response to the Palm Beach and Riyadh events. The two fuel manifold leak engines found by Bombardier did not show any evidence of an undercowl fire. GE performed similar leak, torque, and alignment checks on all those engines along with visual examination of the fuel nozzle and fuel manifold sealing surfaces to determine if there were common causes/anomalies for all the observed fuel manifold leaks. Additionally, GE conducted a series of acceptance test procedure engine runs, developmental engine runs, and component static rig tests to: 1) better understand the effects of fuel nozzle-to-fuel manifold pigtail misalignment, 2) gather assembly and operational loads/stresses on the fuel manifolds under a variety of installation sequence scenarios, 3) validate and develop fuel manifold and fuel nozzle installation best practices and procedures, 4) gather operational data on torque (clamp) relaxation on the fuel manifold b-nut connections, and 5) develop methods to minimize the amount of relaxation experienced in operation.

Based on all the data gathered from the event engines, the 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 fuel manifold female ferrule and fuel nozzle male bullnose sealing surfaces, resulting in high resistance in the threads, low effective clamping force, and a false (high) torque reading. This low effective clamped connection can relax/loosen during engine operation as the manifold geometry normalizes and the connection shifts. All the leaking fuel manifold b-nut connections were found on those connections with lower than expected torque values. Since no fuel leaks occurred during the development engine tests, and leaks could be induced and stopped with slight variations in torque during the component rig tests, GE concluded that multiple factors can be present to create a leak and they are false (low) torques due to misalignment, higher than anticipated assembly loads due to dimensional variation, and poor/distressed sealing surface condition.

Several corrective actions were taken by GE and the Federal Aviation Administration to address and mitigate the risk of GE Passport 20-19BB1A engines fuel manifold leaks. GE issued service bulletins to borescope the engine compartment for signs of an undercowl fuel leak or fire damage (72-00-0141-00A-930A-D-001), and to retorque the fuel manifold b-nut connections as well as the fuel manifold-to-fuel manifold b-nut connection (72-00-0142-00A-930A-D-001); the Federal Aviation Administration followed up with Airworthiness Directive AD 2022-13-12 requiring a visual inspection of the core compartment, a retorque of the core compartment coupling nuts, a ground power assurance check, and a follow-up borescope inspection to ensure that there were no leaks before the airplane was returned to service. GE reviewed the fuel manifold and fuel nozzle installation and assembly procedures and made several changes to provide more specific guidance. The changes focused on eliminating possible ambiguities in the written procedures and to minimize any misalignments or unintended installation loads based on the results from the static rig and engine tests. In addition, feedback from the assembly mechanics were included to improve the overall effectiveness of the proposed installation and assembly changes. GE issued a “change in design” to finalize and clarify the optimum fuel nozzle and fuel manifold installation and assembly procedure using the best practices developed during testing.