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Technical Analysis

Summary

Technical Analysis Report: Examination of an RB211-524G-T Turbofan Engine Compressor Failure

Boeing 747-438, VH-OJU
EXECUTIVE SUMMARY

An Australian registered Boeing 747-438 aircraft operating a regular passenger transport flight sustained the failure of an engine shortly after takeoff from Los Angeles, USA. The engine was subsequently shut-down and the aircraft returned for an uneventful landing.

The failed engine was a Rolls Royce RB211-524G2-T model. Preliminary inspection by the operators maintenance personnel found evidence of extensive internal mechanical damage within the high-pressure compressor section of the engine and as a result, returned the engine to Australia for inspection and overhaul.

The Australian Transport Safety Bureau examined the engine following its disassembly into primary modules. The engine had failed as a result of the liberation of a single blade from the first-stage high-pressure compressor section. That failure subsequently precipitated a titanium metal fire within the compressor, extensively damaging the following stages and rendering the engine inoperative.

The engine manufacturer has attributed three previous failures of RB211 high-pressure compressors to the loss of blades from the first-stage rotor. The blade losses were all associated with fatigue cracking of the dovetail root connection. The manufacturer identified uneven centrifugal loads on the blade roots as a significant factor in the development of blade cracking; possibly exacerbated by patchy root friction and minor mechanical imperfections in the critical blade root transition region.

Evidence from the current investigation indicated the nature of the failure to be very similar to the previously reported events.

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