Overview
On November 17, 2021, United Nigeria Airlines flight NUA-505, an Embraer ERJ-145 registered 5N-BWW, experienced a flameout of the left engine during climb after departure from Abuja, Nigeria, en route to Lagos. The incident was caused by a failure of the #4 bearing in the left engine, which resulted in engine failure at 4,000 feet. The flight returned to Abuja and landed safely on runway 04.
No injuries or aircraft damage were reported. However, the failure was classified as a serious incident by the Nigerian AIB (Accident Investigation Bureau) due to the significant mechanical failure.
Incident Summary
Flight Details
• Aircraft Type: Embraer ERJ-145
• Registration: 5N-BWW
• Flight Number: NUA-505
• Operator: United Nigeria Airlines
• Departure Airport: Nnamdi Azikiwe International Airport (DNAA), Abuja
• Destination Airport: Murtala Muhammed International Airport (DNMM), Lagos
• Occupants: 43 passengers, 4 crew
• Phase of Flight: Climb
Sequence of Events
1. Pre-Takeoff: While lining up for departure from runway 22, the crew observed an “E1 OIL IMP BYP” advisory on the Engine Indicating and Crew Alerting System (EICAS). Following the Quick Reference Handbook (QRH) procedures, they determined the message was a crew awareness advisory and proceeded with takeoff.
2. First Indication: Shortly after takeoff, a loud bang was heard from the rear of the aircraft, but engine parameters appeared normal.
3. Engine Failure: At approximately 4,000 feet, another loud bang occurred, and the left engine flamed out. The crew declared an emergency and requested a direct return to Abuja.
4. Landing: The aircraft landed safely on runway 04 approximately 14 minutes after departure.
Technical Analysis
Engine Details
The aircraft was powered by Rolls Royce AE3007A1 engines. Engine #1 experienced a flameout due to the failure of the #4 bearing, caused by metal debris contamination and insufficient diagnostic efforts to identify the root cause.
Key Findings
1. Recurring Oil Bypass Warnings:
• August 2021: The first “E1 OIL IMP BYP” advisory was registered, indicating potential oil contamination.
• September 2021: The warning reoccurred but inspections of the diagnostic chip collector plugs did not reveal debris.
• October 2021: Metal debris was detected during inspections. Rolls Royce recommended detailed inspections, including a borescope examination of the oil pump screen and midspan bearing, but no abnormalities were identified.
2. Insufficient Maintenance Actions:
• The operator relied solely on borescope inspections, which were inadequate to diagnose the root cause.
• A full engine teardown at a maintenance facility was not performed, delaying the identification of bearing deterioration.
3. Mechanical Failure:
• Metal debris clogged the oil filter, triggering bypass mechanisms that allowed unfiltered oil to circulate in the engine.
• The contaminated oil led to overheating and the eventual seizure of the #4 bearing, causing the engine flameout.
4. Compressor Surge:
• The engine experienced a self-recoverable compressor surge during initial climb, indicated by fluctuations in Inter Turbine Temperature (ITT). This may have contributed to the loud bangs heard by the crew.
Contributory Factors
1. Maintenance Oversight:
• Failure to conduct a comprehensive investigation into recurring oil bypass advisories.
• Over-reliance on visual inspections without deeper diagnostic procedures.
2. Operational Decisions:
• Continuation of flights despite recurring advisory messages.
• Crew’s decision to proceed with takeoff despite the “E1 OIL IMP BYP” advisory.
3. System Design Limitations:
• The oil bypass system prevented catastrophic failure initially but allowed unfiltered oil to circulate, accelerating bearing wear.
Recommendations
Maintenance Improvements
1. Enhanced Diagnostic Protocols:
• Operators must prioritise comprehensive investigations, including engine teardown, for recurring oil bypass advisories.
2. Training for Maintenance Teams:
• Emphasise the limitations of borescope inspections and the need for deeper diagnostic methods.
Operational Recommendations
1. EICAS Message Review:
• Review the classification of oil bypass advisories to provide clearer guidance on operational risks.
2. Crew Training:
• Enhance training on recognising and addressing persistent engine warnings during preflight checks.
Manufacturer Actions
1. Component Reliability:
• Rolls Royce to assess the design and durability of #4 bearings in AE3007A1 engines.
2. Improved Documentation:
• Provide clearer maintenance guidance for addressing oil contamination warnings.
Conclusion
The engine flameout on flight NUA-505 was caused by the failure of the #4 bearing in engine #1, exacerbated by recurring metal debris contamination. The incident underscores the importance of thorough maintenance practices and timely diagnostic actions to address potential failures.
The quick response by the crew ensured a safe outcome for all occupants. Moving forward, stronger collaboration between operators, manufacturers, and maintenance teams is critical to preventing similar incidents.
Disclaimer
This report is based on available evidence and facts at the time of writing. While every effort has been made to ensure accuracy, we apologise for any missed details or inaccuracies. If you are the rightful owner of any associated images and wish for their removal, please email takedown@cockpitking.com.
