United Nigeria E145 at Abuja on Nov 17th 2021, engine flamed out

Last Update: January 2, 2025 / 19:27:52 GMT/Zulu time

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Incident Facts

Date of incident
Nov 17, 2021

Classification
Incident

Airline
United Nigeria Airlines

Flight number
NUA-505

Departure
Abuja, Nigeria

Destination
Lagos, Nigeria

Aircraft Registration
5N-BWW

Aircraft Type
Embraer ERJ-145

ICAO Type Designator
E145

A United Nigeria Airlines Embraer ERJ-145, registration 5N-BWW performing flight NUA-505 from Abuja to Lagos (Nigeria) with 43 passengers and 4 crew, was lining up for departure from runway 22 when the crew received a "“E1 OIL IMP BYP" advisory. The aircraft commenced takeoff and was climbing out of Abuja's runway 22 when a loud bang came from the rear of the aircraft, all engine parameters showed green. At about 4000 feet another loud bang was heard from the back and the engine instruments indicated the left engine had flamed out. The crew requested a direct return to runway 04 at Abuja. The aircraft landed safely on runway 04 about 14 minutes after departure.

On Apr 26th 2022 Nigerai's AIB released their preliminary report rating the occurrence a serious incident. There were no injuries, there also was no damage to the aircraft. The flight data recorder did not record this flight, the last recording on the FDR had been on Feb 14th 2021.

On Dec 28th 2024 Nigeria's AIB released their final report concluding the probable causes of the serious incident were:

Causal factor

Failure of the no. 4 bearing of engine no. 1 leading to the engine flameout at 4,000 ft.

Contributory factors

The inability to probe beyond borescope inspection is the cause of the impending bypass advisory message.

The AIB analysed:

Engine Health Monitoring/Advisory for 5N-BWW

Correspondence regarding the no.1 engine between Rolls Royce and United Nigeria Airlines showed that an impending bypass advisory message was registered on the Centralized Maintenance Computer (CMC) on 24 August 2021. This prompted United Nigeria Airline Limited to contact, the Engine manufacturer (Rolls Royce), for advice. The investigation found that Rolls Royce advised the United Nigeria Maintenance team to inspect all the diagnostic chip collector plugs for metal chips as per the Fault Isolation Manual (FIM) 79-37-00-810-801, which was carried out. No debris was found.

On 15 September 2021, the Oil Debris message reappeared. The investigation also discovered that maintenance action was carried in accordance with FIM 79-37-00-810-801. The diagnostic plugs were re-inspected, and no debris was found for the second time. Hence, this allowed United Nigeria Airlines to continue operating the aircraft as the manufacturer advised.

However, on 4 October 2021, the United Nigeria maintenance team informed Rolls Royce that chips were found at the collector plugs during the inspection.

Rolls Royce advised United Nigeria to inspect the gearbox, use an X10 magnifier glass to inspect the harness, inspect the oil pump screen with a borescope, inspect the midspan bearing, Permanent Magnet Alternator (PMA), and gear shaft for movement.

On 21 October 2021, United Nigeria informed Rolls Royce that their maintenance team carried out a borescope inspection of the Engine as advised, and nothing was found.

According to the investigation, borescope inspection alone was insufficient to determine the cause of the impending bypass advisory light. Hence, further investigation was needed to detect the root cause of the engine problem. The Engine should have been removed and taken for a shop visit, where the root cause would have been detected. This could have prevented the Engine from flaming out. The Engine continued service until the incident occurred on 17 November 2021.

Filter bypass system of 5N-BWW

An Engine Indicating and Crew Alerting System (EICAS) advisory message, "E1 OIL IMP BYP," came ON while the aircraft lined up for takeoff. The crew consulted the Quick Reference Handbook (QHR) for the Embraer 145, Emergency/Abnormal procedure, which says it was a crew awareness message. Therefore, the crew continued with the takeoff roll.

The oil filter on engine No. 1 of 5N-BWW was clogged by metal particles (debris) in the oil, sending a message to the EICAS. The impending bypass functions as a safety measure to prevent the Engine moving part from lubricating oil starvation when the oil filter becomes clogged, allowing unfiltered oil to go into the Engine for lubrication. The impending bypass indication will be illuminated when the differential pressure switch in the engine oil filter is actuated.

Numerous drilled or core passages usually lead to various lubrication points on the Engine. These passages are usually small and easily clogged by impurities when unfiltered oil is allowed to pass through them.

The EICAS message “E1 OIL IMP BYP” will be illuminated when the pressure differential across the oil filter exceeds 22 psi and the oil is about to bypass the filtering element when the filter is contaminated.

Also, the visual and electrical impending bypass indicators will be activated when the pressure differential across the oil filter reaches 19 to 25 psi.

In the case of 5N-BWW, the persistent advisory messages of oil impending bypass show evidence of impurities of metal particles on the affected Engine, the cause of which was not determined by the operator. This led to the mechanical failure, which resulted in engine flameout.

Compressor surge during climb

If a compressor surge occurs during high power at takeoff, the flight crew will hear a loud bang accompanied by yaw and vibration. A surge from a turbofan engine results from instability in the Engine's operating cycle. Compressor surges may also be caused by engine deterioration.

The flight crew stated, "During the climb, there was a loud bang from the rear, and all engine parameters were checked and all in green.”

According to the FDR data, there was an Inter Turbine Temperature (ITT) spike at the start of the flight, and the control loop went into surge avoidance for a second. This phenomenon is known as a single self-recoverable surge. The fluctuation in engine parameters might not be noticed unless someone looked at the gauges at the time of the surge. This might have been a surge that caused the loud bang from the rear, as reported by the flight crew. Although the crew couldn't notice the fluctuation, they said all parameters were checked, and all were in green.

At about 4,000 ft, the flight crew further stated they heard another bang followed by a flameout.

Data from the FDR shows that engine no.1 failed at 4000ft, followed by N2 RPM, which indicated zero. The no. 1 engine failure necessitated an air return by the flight crew.

The preliminary finding of the affected Engine, which was taken to a maintenance facility in Standard Aero, USA, revealed that the #4 bearing seized, leading to a bearing failure.

The bearing might have seized because metal debris entered its clearances
Incident Facts

Date of incident
Nov 17, 2021

Classification
Incident

Airline
United Nigeria Airlines

Flight number
NUA-505

Departure
Abuja, Nigeria

Destination
Lagos, Nigeria

Aircraft Registration
5N-BWW

Aircraft Type
Embraer ERJ-145

ICAO Type Designator
E145

This article is published under license from Avherald.com. © of text by Avherald.com.
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