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Analysis of a failed Pratt & Whitney JT9D-7R4 turbofan engine

Summary

Boeing 767-238, VH-EAQ

EXECUTIVE SUMMARY

The left engine of a Boeing 767-238 aircraft (VH-EAQ) failed during the climb phase of a regular passenger transport flight from Melbourne to Sydney. After the failure, which was characterised by a single loud 'bang' and severe vibration, the engine was shut down and the aircraft returned to Melbourne.

Engineering inspections of the JT9D-7R4 engine found that one of the fan blades had failed part-way along its length and impacted the fan case at the 11 o'clock position, causing the failure of several nose-cowl bolts and substantial damage to components adjacent to the impact point. After the initial impact, the failed blade struck the inside of the nose cowl, forward of the fan. This impact was of sufficient energy to puncture the nose cowl and allow the escape of the blade segment. No damage was caused externally to the airframe or control surfaces.

ATSB laboratory examination of the blade section remaining within the fan rotor disk found that the blade had fractured as a result of fatigue crack growth from a pre-existing defect at the blade trailing edge. The defect was identified as a shallow crack that had formed during or before the last blade refurbishment operation, carried out in 1991. Non-destructive examination procedures carried out on the blade following the refurbishment had failed to detect the defect.

In 1998, the manufacturer purchased the engine for use as a lease unit. The defective blade was installed into the engine shortly thereafter. At the time of failure, the blade had operated for 7,187 hours and through 2,083 cycles following its 1991 refurbishment. Operating times and cycles before the blade refurbishment were not available.

Type: Educational Fact Sheet
Publication date: 27 November 2001
 
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Last update 07 April 2014
 
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