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IAE redesigns compressor blades

INTERNATIONAL AERO Engines (IAE) is to offer redesigned compressor blades for the V2500-A1 turbofan, following a series of in-service failures with two carriers.

Two incidents on a Dragonair Airbus Industrie A320, in February 1995 and December 1994, are the latest manifestation of a problem which it has taken IAE nearly two years to address.

The fault has been limited to two carriers - Air Lanka (four events) and Dragonair (two events). The engine manufacturer says that it has narrowed down the problem to a specific batch of -A1 engines.

It is working on a blade redesign which will ultimately become standard and is meanwhile reducing the chances of recurrence through careful airline monitoring of specified parameters.

Flexing of the N2 (high-pressure compressor) shaft, caused by differential cooling, has been identified as the origin of the problem. That increases the blade-tip/compressor-casing clearance beyond design limits, leading to blade vibration and, ultimately, failure just above the platform root.

IAE says that the treatment was to reduce differential cooling by introducing a manual-start cycle, which it has incorporated into the normal start-system software. It has advised operators that incipient blade-trouble is detectable by careful monitoring of exhaust-gas temperature trends, which climb when rotor bowing occurs. In addition, the manufacturer has advised operators to reduce borescope inspection-cycles to 50h.

IAE says that tests on a redesign to strengthen the blades are in progress, paving the way for a new standard blade.

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