What happened
On 8 November 2017, an Avro 146-RJ85A operated by Airlink was performing a scheduled international flight from Harare International Airport, Zimbabwe, to OR Tambo International Airport, South Africa. While cruising at 34,000 feet over the Limpopo province, the aircraft experienced a sudden, loud bang followed by a significant rightward yaw.
During the cruise phase, the number 2 engine suffered an uncontained failure. Debris from this failure struck the number 1 engine, damaging its FADEC box and causing an uncommanded shutdown. This left both engines on the port side of the aircraft inoperative. The crew immediately declared a MAYDAY and initiated emergency procedures. After consulting with the operator's maintenance control centre and evaluating the aircraft's stability, the crew elected to continue to their destination. The aircraft landed safely at OR Tambo International Airport with no injuries to the 34 passengers or 4 crew members.
The investigation
SACAA AIID examined the wreckage and engine components to determine the sequence of events. The investigation focused on the physical damage to the port-side engines, where the number 2 engine's casing had been breached by the fourth-stage turbine rotor wheel. Investigators also reviewed maintenance records for the fourth-stage turbine rotor disc assembly, which had been replaced approximately 340 flying hours prior to the incident.
Findings
Technical analysis revealed that the uncontained failure of the number 2 engine was caused by the low-pressure turbine retaining nut becoming dislodged. This allowed the fourth-stage turbine rotor disc to disengage from the shaft. The investigation identified that the maintenance procedure used during the recent disc installation was incorrect; specifically, a procedure intended for a pre-service bulletin engine configuration was applied to a post-service bulletin configuration. This led to the improper installation of the assembly, potentially involving incorrect torque settings or the misstacking of the over-speed ring.
Safety action
Following the investigation, BAE Systems issued an All Operator Message to alert the industry to the findings. The manufacturer is also working to amend the Aircraft Maintenance Manual (AMM) to include specific dimensional check references for the installation of the fourth-stage turbine rotor disc assembly to prevent similar occurrences in the future.