Section 21 (2) of the Transport Safety Investigation Act 2003 (TSI Act) empowers the ATSB to discontinue an investigation into a transport safety matter at any time. Section 21 (3) of the TSI Act requires the ATSB to publish a statement setting out the reasons for discontinuing an investigation. The statement is published as a report in accordance with section 25 of the TSI Act, capturing information from the investigation up to the time of discontinuance.
Overview of the investigation
On the morning of 7 April 2023, a Fokker 70, registered VH-NUU, was being pushed back from a bay at Brisbane Airport, Queensland, to operate a passenger air transport flight to Roma. It was reported that during pushback at about 0640, a trail of fluid on the ground was observed and then found to be due to a fluid leak from the no. 2 (right) engine. Both engines were shut down and the aircraft was towed back to the bay.
When inspected, engineers determined there was a leak from a connection on the lower left side of the engine, between a rigid fuel line and the fuel flow regulator (FFR), and fuel had drained out of the engine nacelle through an access opening near the leak.
After removing the fuel line from the component, the source of the leak was determined to be a pair of elastomeric seals (O-rings), fitted to the fuel line, that had degraded to a point where they no longer could contain fuel under pressure. The seals were replaced, along with the FFR because of an unrelated defect. An engine ground run was carried out and the aircraft was returned to service.
After receiving notification of the occurrence on 12 April 2023, the ATSB commenced an investigation. The ATSB:
- obtained maintenance records
- examined maintenance information
- interviewed technical specialists
- obtained information from the engine manufacturer (Rolls-Royce).
During the investigation, and in consultation with the engine manufacturer, the ATSB noted that:
- no reason could be established for the degradation of the seals, which occurred over a period of about 6 years since they were likely changed
- maintenance records indicated that the components were installed and maintained in accordance with manufacturer requirements
- there were no instances of an engine fire resulting from fuel leaks from the FFR or other components in the same area on Fokker 70 and Fokker 100 aircraft in over 26 million flying hours
- the layout of the fuel lines on this engine type is routed to avoid ignition sources and there were no hot surfaces or sources of ignition in this zone
- fuel leaks from this location would drain away from the engine and then out and away from the nacelle through an access opening on the bottom of the lower cowl.
Therefore, the ATSB considered it extremely unlikely that a fire would develop as a result of this type of fuel leak. Further, if a fire did occur it could be detected by on-board systems (or visually by ground crews) and extinguished (along with the fuel supply being isolated from the engine nacelle).
Reasons for the discontinuation
Based on a review of the available evidence, the ATSB considered it was unlikely that further investigation would identify any systemic safety issues or important safety lessons. The ATSB did not identify any concerns with the assessment, management, and monitoring of this type of defect. Consequently, the ATSB has discontinued this investigation.
The evidence collected during this investigation remains available to be used in future investigations or safety studies. The ATSB will also monitor for any related occurrences that may indicate a need to undertake a further safety investigation.