The Nigerian Safety Investigation Bureau (NSIB) in its report stated that the failure of United Nigeria Airlines to probe root cause of an earlier engine problem eventually led to an engine flame out.
On 17 November 2021, United Nigeria Airline’s flight to Lagos from Abuja, made an air return after the pilots noticed an engine problem.
As the aircraft lined up for takeoff, an advisory light “impeding bypass” illuminated for the number one engine.
During the takeoff roll, a loud bang was heard from the rear of the aircraft.
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The takeoff was continued and at 4000ft, another bang was heard, and the engine flamed out, necessitating an air return to Nnamdi Azikiwe International Airport.
Speaking during a press conference to the release seven investigation reports, Alex Badeh, Director General, NSIB explained how further investigation was needed to detect the root cause of the engine problem and how failure to do this contributed to the airline’s engine flaming up.
Badeh explained in one of its reports that 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.
He said this prompted United Nigeria Airline Limited to contact, the Engine manufacturer (Rolls Royce), for advice, adding that 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 but no debris was found.
He further disclosed that on 15 September 2021, the Oil Debris message reappeared and the investigation also discovered that maintenance action was carried in accordance with FIM 79-37-00-810-801.
The NSIB director general said 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.
He however disclosed that on October 4, 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, he said.
According to the DG in his report, on October 21, 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.
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“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,” Badeh said.
Other findings according to the NSIB report showed that the flight crew were licensed and qualified to conduct the flight, the aircraft had a valid Certificate of airworthiness, the aircraft was scheduled for six sectors for that day and the incident occurred in the second sector.
“An EICAS Advisory Message “E1 OIL IMP BYP” came ON while the aircraft lined up for takeoff. The flight crew heard a loud bang from the rear during the takeoff roll. At about 4,000 ft, the flight crew heard another bang. At 08:43 h, the flight crew declared MAYDAY and the emergency services were duly informed at 08:45 h.
“The Air Traffic Controller later cancelled the Emergency alert. NUA0505 landed safely on runway 04 at 08:53 h. At the engine repair facility, Standard Aero, USA, no. 4 bearing failure was discovered,” he said.
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