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ATSB: Part Failures Behind 787 Engine Incidents

Part failures were the root cause of two Boeing 787 engine incidents for Jetstar Airways and Scoot Airlines in August and September 2016, respectively.

WASHINGTON—Part failures were the root cause of two Boeing 787 engine incidents for Jetstar Airways and Scoot Airlines in August and September 2016, respectively.

Just-released preliminary reports on both incidents by the Australian Transport Safety Bureau (ATSB) reveal that fixes to both issues have been deployed, a modified transfer gearbox component for the GEnx-1B engine based on the Jetstar 787 incident, and new hydraulic hoses in the nacelle as a result of the Scoot incident.

Of the two, the Jetstar incident was the more serious, in that it resulted in an in-flight shutdown of one engine and a diversion. According to the ATSB preliminary report, Jetstar Flight JQ12 was about two hours into its flight from Tokyo to Queensland, with 11 crew members and 309 passengers on board, when the crew received an electric-generator-drive fault message on the No. 2 generator on the right engine.

The generators, which power electrical systems on the engine and aircraft, are run by a mechanical shaft connected to the rotating portion of the engine. The crew followed the appropriate checklist and disconnected the generator from the engine, powering up the auxiliary power unit to take its place. The fault message is linked to the engine-debris monitoring system, which was detecting metal chips in the engine oil.

About 30 min. later, at a cruise altitude of 40,000 ft., the crew received messages that the right engine oil pressure was low, faults that resulted in the shutdown of the right engine. The crew declared an emergency and flew to Guam, the nearest airport, 200 nm south of their position.

On the ground, a maintenance crew found “a large quantity of oil throughout the engine, and a considerable amount of metallic debris within the engine oil system,” according to the ATSB.

The source of the leakage and debris was a fracture in the housing of a transfer gearbox, which is connected to the engine by a mechanical shaft. GE determined that the failure “was consistent” with a mechanical resonance issue addressed by a service bulletin issued in March.

The fix included changes to the gearing to dampen vibrations. Jetstar had begun the replacing the components in its GEnx engines, but had not completed the work on the incident engine, as it was in the lowest-risk category due to its low time. The carrier, in response, modified its service-bulletin compliance time, making it a priority to implement the service bulletin on at least one engine on each 787. All modifications were completed as of November, according to the ATSB.

The Scoot 787 incident occurred when the aircraft used maximum reverse thrust during its landing in Melbourne after a flight from Singapore, according to the ATSB preliminary report. Controllers called the pilot, saying they had seen smoke coming from the aircraft’s right engine, although there were no anomalous indications in the cockpit, nor any evidence of issues externally on the engine compartment.

Mechanics later found that a damaged hydraulic hose in the right engine pylon hydraulic bay had leaked hydraulic fluid, likely causing or contributing to the smoke (The Rolls-Royce Trent 1000 also naturally emits smoke in some cases due to incomplete air/oil separation, according to the ATSB).

Boeing analyzed the issue, determining a root cause and identified the population of hoses that might be affected, alerting airlines of the issue. The ATSB said Scoot identified which hoses in its fleet might be affected and ordered replacement parts.

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