A Qantas Airbus A330-200, registration VH-EBR performing flight QF-123 from Brisbane,QL (Australia) to Auckland (New Zealand) with 258 people on board, was climbing out of Brisbane's runway 19 when the crew declared PAN PAN, PAN PAN, PAN PAN reporting they had a problem on the #1 engine (CF6, left hand) subsequently detailing there was possible damage on the engine. The crew decided to return to Brisbane for a safe landing on runway 01 about 40 minutes after departure.
A replacement A330-200 registration VH-EBM reached Auckland with a delay of 3 hours.
The occurrence aircraft returned to service about 31 hours after landing back.
The ATSB reported during climb out the crew observed abnormal indications for the left hand engine and airframe vibrations. The crew reduced the left hand engine to idle thrust and returned to Brisbane. An engineering inspection revealed two engine blades were missing from the #1 engine resulting in severe impact with the other blades. The engine was replaced. The occurrence was rated an incident and is being investigated by the ATSB.
On Aug 19th 2020 the ATSB released their final report concluding the probable causes of the incident were:
Contributing factors
- A worn stator lever arm bushing resulted in fretting damage, initiation of a fatigue crack, and fracture of the lever arm.
- The fracture of the lever arm led to an off-schedule variable stator vane, which created turbulent airflow within the engine compressor section. This turbulent airflow led to the failure of a compressor blade at the blade root, due to high-cycle fatigue.
- The operator had conducted three non-mandatory inspections of the variable stator vane system since the engine's last overhaul. Despite these inspections being conducted, the outer bushing and lever arm at the number 24 position was able to wear, undetected.
Other findings
- The engine issue was one of two identified worldwide. Both occurred within 5 months of each other, in the same operators fleet and in the same number 24 position, and both on the left engine. The engine manufacturer, operator and the ATSB were unable to establish fully the reason for the timing, fleet, and position commonalities in the context of worldwide historical data.
The ATSB stated:
General Electric intended that replacement of the complete set of bushings was required when more than half of the accessible bushings were worn. However, the operator had proactively replaced worn bushings individually when found during maintenance. As a result, the threshold to replace the complete set would not be reached and inaccessible bushings would not be replaced.
The ATSB analysed:
Engine vibration
The combination of worn outer bushings and fretting wear on a fourth stage high-pressure compressor (HPC) variable stator vane (VSV) lever arm resulted in a fatigue crack, leading to a fracture of the lever arm. The associated stator vane rotated into an off-schedule position and created turbulent airflow that acted like a cyclic pulse on the fourth stage HPC blades, as they passed the off-schedule vane. This aerodynamic cyclic loading resulted in initiation of a high-cycle fatigue crack in at least two compressor blades, until one blade separated at its root, causing damage to the downstream engine components and a noticeable increase in measured engine vibration.
Periodic maintenance Qantas inspected the VSV system in accordance with the manufacturers non-mandatory inspection, with the exception of the individual replacement of worn bushings, as they were discovered. The inspections were generally effective in that assemblies accessible for inspection had previously been found to be loose and were replaced. However, while the failed (number 24) VSV lever arm was also accessible, no issues were found in the most recent inspections. Noting that the engine was approximately halfway between the 1,000 cycle inspections, it was possible that the looseness was not apparent at that time. Nevertheless, the inspections, as conducted, were not effective in detecting the worn bushing and thereby preventing this occurrence.
A consequence of the individual replacement of worn bushings, as opposed replacement of the entire set on a threshold of 50 per cent worn bushings, was that the inaccessible bushings would not be replaced while the engine was in service. While this would not have affected the outcome in this occurrence, modifying the replacement criteria reduced the overall effectiveness of the inspection.
Previous occurrences
This was only the second engine failure of its type on CF6-80E1 engines. The occurrences were within five months of each other, involved the same operator and failure of the VSV arm in the same position. In the absence of commonalities in engine hours, cycles or service history, the engine manufacturer determined that the failures were most probably related to maintenance in the area of the VSV arm. The ATSB review of the associated maintenance work packages did not find any evidence to positively link the occurrences.