Bombardier Inc BD-700-2A12 N63RP incident near West Palm Beach, Florida

Probable cause

An in-flight engine fire resulted from a fuel leak from fuel nozzle No. 16 pigtail-to-fuel manifold b-nut connection that contacted hot engine parts and ignited. Contributing to the manifold fuel leak was the misalignment between fuel manifold female ferrule and fuel nozzle male bullnose sealing surfaces coupled with distress of the ferrule sealing surface.

NTSB analysis

Post-event inspection of a GE Aviation Passport 20-19BB1A turbofan engine found light thermal distress on the outside of the engine core compartment near the top of the engine from the 10:00 to 11:00 o’clock position, aft looking forward, and localized discoloration on the inside of the core cowls in the general location of fuel nozzle No. 16 location consistent with an undercowl engine fire. This corroborates the pilot’s report of an in-flight engine fire during takeoff climb. The fuel nozzle No. 16 location appeared shiny, lacked the sooting that neighboring fuel nozzle pigtail-to-fuel manifold b-nut connections exhibited; therefore, it was considered a possible fuel leak location. The engine was removed and sent to GE for evaluation; a fuel system leak check was performed but the source/location of the fuel leak could not be identified. The fuel pressure and nitrogen check pressure used during the leak tests were well below the fuel pressure the engine experienced during the event and was determined to be insufficient to replicate the leak.

A torque check of all the fuel manifold b-nut connections found four locations, all located on the left fuel manifold, which 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 four low torque locations was fuel nozzle No. 16 that was identified as a possible leak source during the initial examination. Detailed analysis of the fuel nozzle No. 16 pigtail-to-fuel manifold b-nut connection revealed evidence of galling and intermediate contact marks consistent with and indicative of misalignment and relative movement within the connection; none of the other low torque b-nut connection locations exhibited this type of surface distress.

Since the post-event fuel system leak checks performed by GE could not induce a fuel leak, the exact location/source of the fuel leak could not be determined by testing and observations. However, the combination of low torque, misalignment between fuel nozzle No. 16 pigtail-to-fuel manifold b-nut connection, and sealing surface distress created the conditions by which there was insufficient sealing allowing fuel to leak during high engine power and high fuel pressures. No other fuel nozzle locations had this combination of factors that would have allowed a fuel leak.

Text from the NTSB. Open the NTSB docket for ENG22LA020 for the full record.