Oil sump coking leads to Saab 340 engine failure


Oil sump coking leads to Saab 340 engine failure

Key points:

  • Engine failed as a result of an internal oil fire, weakening a turbine disk and resulting in turbine blades being released
  • Fire occurred when oil leaked from an oil sump due to carbon deposits (coking)
  • Maintainers had followed the correct troubleshooting procedure but were unable to determine the reason for the high oil consumption

Coking in an oil sump led to a Saab 340 regional airliner’s right engine failing, a new ATSB investigation has established.

The Regional Express Saab 340B was operating a scheduled passenger service from Moruya to Merimbula on the New South Wales South Coast on 29 August 2019, with the aircraft’s right engine (a GE CT7) being monitored for high oil consumption. About eight minutes into the flight and shortly after levelling off at an altitude of 9,000 feet, the flight crew observed a right engine fire indication. As they conducted the engine fire checklist, the crew heard the engine surge and a loud bang, and the cabin crew member reported seeing a brief flash of light from the aircraft’s right side.

The flight crew continued the engine shutdown checklist and subsequently shut the engine down and elected to continue to Merimbula, based on their proximity to the destination and with the aircraft already having been set up for the approach.

The crew entered a holding pattern to complete all the required checklists and to ensure the availability of emergency services at the Merimbula Airport, where the aircraft landed without further incident.

An ATSB investigation found that the engine failed as a result of an internal oil fire, which weakened a turbine disk and resulted in turbine blades being released. The fire occurred when oil leaked from an oil sump (known as the B-sump) due to carbon deposits, or coking, within that sump. The coking was most likely due to either the sump not being completely clean when installed at the last major overhaul and/or accelerated coking.

As a result of the incident, GE has enhanced the troubleshooting procedures to identify internal engine oil leaks more effectively. They have also developed enhancements to the overhaul facility cleaning procedure for the affected oil sump.

This incident highlights the importance, when piloting multi-engine aircraft, of maintaining the ability to operate with one engine inoperative. Aircraft turbine engines are complex, and can fail for reasons that are rare and difficult to identify prior to the failure, the investigation notes.

In this occurrence, the maintainers had followed the correct troubleshooting procedure but were unable to determine the reason for the high oil consumption. The flight crew’s skill and knowledge, however, along with built-in system redundancies, ensured the overall safety of the flight.

The report notes that there have been only two known occurrences of CT7 engine failures or in-flight shutdowns due to significant coking in the B-sump.

You can find here the investigation report AO-2019-046: Engine failure involving Saab 340B, VH-RXX, near Merimbula, NSW, on 29 August 2019

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