Accident Avro RJ85 ZS-ASW,

ASN Wikibase Occurrence # 319778

Date:	Wednesday 8 November 2017
Time:	19:38
Type:	Avro RJ85
Owner/operator:	Airlink
Registration:	ZS-ASW
MSN:	E2313
Year of manufacture:	1997
Total airframe hrs:	29636 hours
Engine model:	Lycoming LF507-1F
Fatalities:	Fatalities: 0 / Occupants: 38
Aircraft damage:	Substantial
Category:	Accident
Location:	over Limpopo province - South Africa
Phase:	En route
Nature:	Passenger - Scheduled
Departure airport:	Harare Airport (HRE/FVHA)
Destination airport:	Johannesburg-O.R. Tambo International Airport (JNB/FAOR)
Investigating agency:	CAA S.A.
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
Airlink flight 8103 took off from Harare International Airport (FVHA) in Zimbabwe on an international scheduled flight to from Johannesburg, South Africa.
The Avro RJ85 took off at about 18:45 hours local time. At approximately 19:38 during cruise flight at a height of 34000 ft (FL340) within South African airspace, a loud bang was heard on the flight deck and a subsequent right yaw was experienced. The crew observed an immediate visual indication on the cockpit engines instruments that engines no. 1 and 2 had experienced catastrophic failure. According to the flight recordings, the no. 1 engine failed first. This was due to damage to the full authority digital electronic control (FADEC) box, which had been struck by the turbine blades debris from engine no.2.
Following the incident, the crew declared a MAYDAY call due to the instant failure of the two engines on the port wing, and immediately followed emergency operating procedures. Contact was made with the operator's maintenance control centre (MCC) to report and discuss the situation. A decision was then made by the crew following considered assessment of the situation to continue with the flight to the destination, a distance of approximately 240 nm. The aircraft landed uneventfully on runway 21R at 20:39.

It was found that that fourth-stage Low Pressure turbine rotor disc of engine no.2 had failed. The fourth-stage disc assembly was fitted on 27 July 2017 as a repaired unit which had a total of 11885 hours and 9419 cycles. During this disc change a wrong procedure was followed: pre-SB (Service Bulletin) engine configuration type procedure was applied during a post SB engine configured installation. During replacement of the fourth-stage disc assembly, a retaining nut that had been fitted before was reused and a new locking cup was used.

Probable Cause:
The cause of the no2 engine uncontained failure was attributed to the LP turbine retaining nut becoming dislodged resulting on the fourth-stage turbine rotor disk disengaged from the LP turbine shaft. The fourth-stage turbine rotor disc compromised the turbine casing and turbine debris from the no. 2 engine struck the no. 1 engine, causing an un-commanded shutdown and leading to a catastrophic failure of both port-side engines.
Contributory factor:
1. The incorrect application of torque settings; or improper installation due to a possible mis-stacking of the over-speed ring during maintenance.

Accident investigation: