CHI95IA286

The airplane sustained minor damage following an uncontained failure of the number two engine during approach. The crew received a fire indication of the number two engine. They secured the engine and discharged the nacelle fire extinguishing system. They landed and evacuated the airplane without further incident. Examination revealed several penetrations of the right fuselage side and number two cowling. The gearbox housing had a hole at the 12 o'clock position in the plane of rotation of the helical drive (bull) gear. The combustion plenum had a hole at the five o'clock position. Fragments of the bull gear were recovered from within the gear box. Metallurgical examination of the bull gear revealed a fatigue crack that emanated from the root radius of a gear tooth. The crack progressed to an area of the fracture that contained 'features typical of overstress separation.' The hole in the combustion plenum was attributed to excessive temperature. No other metallurgical anomaly was noted.

On August 18, 1995, at 1348 central standard time, a British Aerospace BAE Jetstream 3201, N425AM, operated by Trans State Airlines as TW Express Flight 440, sustained minor damage following the uncontained failure of the number two engine, and subsequent in-flight fire, during approach to the University of Illinois Airport, Champaign, Illinois. The flight crew landed and evacuated the airplane without further incident. There were no injuries to the crew of 2, or the 16 passengers aboard the airplane. The scheduled domestic passenger flight, operated under 14 CFR Part 121, originated at the Lambert-St. Louis International Airport, St. Louis, Missouri, with a planned destination of Champaign, Illinois. An IFR flight plan was filed, and visual meteorological conditions prevailed.

The operator reported the crew received a fire indication on the number two engine. They secured the engine and discharged the nacelle fire extinguishing system.

Examination of the airplane revealed several penetrations of the right fuselage side and number two cowling. Fuel lines, oil lines, and electrical wiring in the number two engine nacelle were burned and soot covered in the vicinity of the plenum at the five o'clock position. The number two engine was removed from the airplane and examined at Allied Signal Aerospace, Phoenix, Arizona, on August 23, 1995.

The plenum case had a large hole located in the 5 o'clock position. The exposed combustion chamber exhibited no evidence of penetration. The exterior plenum was covered with black sooty residue around the hole.

The gearbox housing had a hole in the 12 o'clock position in the plane of rotation of the helical drive (bull) gear. Fragments of the bull gear were recovered from within the gear box. The air inlet had a hole immediately opposite the hole in the gearbox. Examination revealed severe foreign object damage and loose metallic debris throughout the engine.

The hole in the plenum was analyzed by a materials engineer at Allied Signal Aerospace. The materials engineer wrote "the hole in the plenum was attributed to a stress rupture fracture that resulted from localized, short-time exposure (minutes or less) to temperatures in excess of 1800 degrees fahrenheit."

The bull gear fragments were examined by a NTSB metallurgist. In his factual report he wrote that a fatigue crack, emanating from the root radius of a gear tooth, progressed to an area of the fracture that contained "features typical of overstress separation." No other metallurgical anomalies were noted.

Additional persons included Bill R. Brown, Jetstream Aircraft, Ltd., P. O. Box 17276, Nashville, Tennessee, 37217.