SA Airlink RJ85 at Johannesburg on Mar 27th 2019, engine shut down in flight
Last Update: August 4, 2020 / 20:09:34 GMT/Zulu time
South Africa's Civil Aviation Authority (SACAA) released their preliminary report stating the engine failed while delivering 90% N1 climb thrust. The cause of the failure is not yet known. The engine had accumulated 25 579.28 hours since new and 230.28 hours since the last engine shop visit on Aug 10th 2018.
On Aug 4th 2020 SACAA released their final report concluding the probable cause of the serious incident was:
The number 4 engine failure was due to the failure of one of the first stage compressor blades, likely caused by a fatigue crack at the root of the blade.
The SACAA analysed:
The aircraft, a British Aerospace Avro 146-RJ85, was powered by four Honeywell LF507-1F turbofan engines. The number 4 engine was installed in the number 4 position on 10 December 2018 at a total engine time of 25 349.12 hours and 19 972 engine cycles. At the time of the serious incident, the engine had accumulated a total of 25 579.28 hours and 20 148 cycles. The engine had been in service for 230.16 hours and 176 cycles following maintenance intervention from an approved engine overhaul facility on 10 August 2018.
All applicable Airworthiness Directives (AD) and Service Bulletins (SB) were reviewed and were found to have been carried out as required.
The last borescope inspection on this engine was carried out in June 2015 and the failed engine had operated for 4443, 28 hours since the last borescope inspection. The borescope inspection limits require that it should be carried out at every 6000 hours initially, and subsequently, at every 3000 hours. The borescope conducted in June 2015 resulted in the replacement of the LP compressor blades on the number 4 engine. The engine was due for a borescope after an additional 1556. 72 hours, thus, it was still within its limits.
The blades have a life limit of 50 000 flying hours (FH) and 25 000 cycles; and the failed blades had accumulated 4443,28 hours and 2333 cycles, thus, they were not due to be changed yet.
According to the engine condition report, the first stage compressor blades were fitted new at the IC-03 on 9 June 2015 at 21 136 hours and 17 815 engine cycles. The first stage compressor blades accumulated a total of 4443.28 hours and 2333 cycles before one of the blades failed.
The first stage compressor blades were inspected according to Honeywell Service Bulletin ALF/LF-72-1105 during the last shop visit on 10 August 2018 at 25 349.12 hours and 19 972 engine cycles. No defects were recorded during the inspection. The blades had operated for a further 230.16 hours since the last shop visit and 4443.28 hours since their fitment to this engine.
The aircraft was fitted with a Honeywell D-FDR. The unit was downloaded by an approved facility. From the data, the number 4 engine N1 suddenly spooled down at the same time the aircraft lateral accelerometer recorded an instantaneous increase in vibration levels from 0.008 to 0.115 units for a short time.
The investigation revealed that the serious incident occurred because of failure of one of the first stage compressor blades which had cracked at the root before it separated. The blade travelled to the rear of the compressor section, damaging the LP and HP compressors and some internal engine components in the compressor section of the engine.
The first stage compressor blade failed at 230.16 hours following the last shop visit where the compressor section was inspected; no defects were noted during that inspection. It is likely that the crack on the blade root was due to fatigue given that it failed at 230.16 hours after the last shop visit.
This article is published under license from Avherald.com. © of text by Avherald.com.
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