What happened
NTSB summary, verbatimDuring takeoff the No. 1 (left) engine fire warning illuminated in the cockpit. The pilot declared an emergency, shut down the No. 1 engine and discharged one fire bottle. The fire warning continued and the pilot discharged the second bottle; but the fire warning did not extinguish. The pilot performed an air turnback and landed the airplane uneventfully approximately 11 minutes later. Engine testing at the manufacturer’s facility revealed a large fuel leak emanating from the No. 2 fuel nozzle manifold adapter-to-transfer tube O-ring connection. Examination revealed two manufacturing defects in the No. 2 fuel nozzle manifold adapter. The first defect, poor surface finish, caused damage to the transfer tube O-ring during the installation process, initiating an internal fuel leak. The second defect, blockage of the internal safety tell-tale drain due to an improper machining and subsequent cleaning procedure, prevented the leaking fuel from flowing into the tell-tale drain and being detected by maintenance personnel. Examination of the transfer tubes revealed an undersized O-ring retention zone, which allowed the O-ring to fit loosely such that it was not capable of withstanding continuous maximum fuel pressure load. Eventually the O-ring failed to seal properly, fuel leaked and was ignited by the hot combustor case. The undersized O-ring retention zone was created during the cleaning and overhaul process of the transfer tube.
Photographs
1the aircraft, and what the investigators foundProbable cause
the Board's determinationThe sealing failure between the fuel nozzle adapter assembly and fuel transfer tubes that allowed fuel to leak into the nacelle fire zone where it was subsequently ignited by the hot combustor case. Contributing to the failure was a combination of manufacturing defects of the fuel nozzle adapter assembly by the manufacturer and incorrectly overhauled fuel transfer tubes by the engine manufacturer. Contributing to the incident was a second defect of the fuel nozzle adapter assembly by the manufacturer which prevented maintenance personnel from detecting the internal fuel leak.
Occurrence sequence
1 stepsNTSB coding · CICTT taxonomy- 1 · TakeoffFire/smoke (non-impact)defining event
Findings
2 causal · 0 contributing- CAUSEAircraft › Aircraft power plant › Engine (turbine/turboprop) — Incorrect service/maintenance
- CAUSEAircraft › Aircraft power plant › Engine fuel and control › Fuel distribution — Failure
Sequence of events
8 timed eventsfrom the FDR factual report · claude-sonnet-5- 19:36:38Takeoffp.3Aircraft took off
- ~19:39:38Climbp.3Autopilot engaged about 3 minutes after takeoff
- 19:41:13In-flight emergencyp.3Left engine fire warning started on the FDR, continuing until just after touchdown; master warning also indicated at this time and remained on for 6 seconds
- 19:41:25In-flight emergencyp.3Autopilot disengaged
- ~19:41:27In-flight emergencyp.3Left engine power lever angle began to decrease, followed by left engine power decrease
- ~19:41:37In-flight emergencyp.3Left engine propeller RPM reading began registering invalid data about 10 seconds after PLA began decreasing
- unspecifiedIn-flight emergencyp.3Left engine torque reached 0% and remained at that value for the rest of the flight
- 19:47:31Landingp.3Aircraft touched down
NTSB analysis
from the final reportDuring takeoff the No. 1 (left) engine fire warning illuminated in the cockpit. The pilot declared an emergency, shut down the No. 1 engine and discharged one fire bottle. The fire warning continued and the pilot discharged the second bottle; but the fire warning did not extinguish. The pilot performed an air turnback and landed the airplane uneventfully approximately 11 minutes later. Engine testing at the manufacturer’s facility revealed a large fuel leak emanating from the No. 2 fuel nozzle manifold adapter-to-transfer tube O-ring connection. Examination revealed two manufacturing defects in the No. 2 fuel nozzle manifold adapter. The first defect, poor surface finish, caused damage to the transfer tube O-ring during the installation process, initiating an internal fuel leak. The second defect, blockage of the internal safety tell-tale drain due to an improper machining and subsequent cleaning procedure, prevented the leaking fuel from flowing into the tell-tale drain and being detected by maintenance personnel. Examination of the transfer tubes revealed an undersized O-ring retention zone, which allowed the O-ring to fit loosely such that it was not capable of withstanding continuous maximum fuel pressure load. Eventually the O-ring failed to seal properly, fuel leaked and was ignited by the hot combustor case. The undersized O-ring retention zone was created during the cleaning and overhaul process of the transfer tube.