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TSB report on Westjet's YLW engine failure


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TSB # A08/2005

TRANSPORTATION SAFETY BOARD OF CANADA'S INVESTIGATION FOUND MAINTENANCE MANUAL DID NOT WARN OF COMPRESSOR BLADE FATIGUE CRACKING

(Gatineau, Quebec, May 19, 2005) - The Transportation Safety Board of Canada (TSB) today releases its final report (A03P0054) into an in-flight engine failure of a WestJet Airlines Boeing 737-200 at Kelowna Airport, British Columbia, on March 11, 2003.

In its investigation, the TSB found that the maintenance manual for the Pratt & Whitney JT8D engine did not have a warning about potential compressor airfoil fatigue cracking that may develop on engine blades as a result of a compressor stall or a compressor surge. Consequently, maintenance personnel may be unaware that compressor airfoil fatigue cracking could occur as a result of a compressor surge. Also, the manual's troubleshooting flowchart did not include a reference to a test procedure that should have been performed after replacement of the pressure ratio bleed control (PRBC) valve, which controls the evacuation of excess air to prevent surges during low-power operations, such as engine start-ups, idling and decelerations.

In this incident, because of a compressor surge, the airflow in one of the aircraft's engine compressor gas paths was altered by either the failure of an airfoil retaining pin, or by a detached stator in close proximity to a rotor. Airflow instabilities caused rotors to vibrate, leading to widespread fatigue cracking in the rotor blades. As a result of this cracking, a rotor blade detached during the initial climb, resulting in severe engine damage and loss of engine power.

The TSB issued a Safety Advisory on December 2, 2003 to Transport Canada, with copies to Pratt & Whitney USA, Boeing Commercial Aircraft, and WestJet Airlines. The advisory suggests a review of current aviation maintenance practices and procedures regarding engine performance troubleshooting and compressor stalls, with a view to ensuring that information identifying possible compressor airfoil fatigue damage is not overlooked or dismissed.

As a result, Pratt & Whitney reworded and clarified sections of its JT8D Maintenance Manual (part number 481671) regarding engine troubleshooting.

Transport Canada responded by issuing a Service Difficulty Advisory (2004-05), which strongly advises maintainers, operators and other responsible persons that compressor surging should be given the same attention as compressor stalls. Surges should be considered to be minor stalls, and the potential for damage should not be underestimated. The Advisory also stated that compressor surges and stalls can induce latent fatigue fractures culminating in engine failures.

The Boeing 737-200 departed Kelowna Airport, British Columbia, on March 11, 2003 at 8:40 a.m. local time, with 6 crew and 50 passengers on board. Shortly after take-off, the pilots heard a loud bang, similar to that of an engine compressor stall. The revolutions per minute (rpm) of one of the engines' rotors reduced rapidly, and the engine's exhaust gas temperature reading exceeded the highest value on the indicator. The pilots shut down that engine (Pratt & Whitney JT8D-17A) and levelled the aircraft at about 6000 feet. The crew declared an emergency and returned to the airport. The aircraft landed with only one engine operating and taxied back to the terminal without further incident.

The TSB is an independent agency that investigates marine, pipeline, railway and aviation transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.

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I hadn't seen that report.

It's good to see that all the applicable procedures were followed correctly.

It just goes to show that even after an engine that has been around as long as the JT8D has can still ruin your day in unexpected ways.

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