CHI99IA350

The airplane sustained an in-flight failure of the right engine. The captain performed the checklist to shut down the engine and performed the single engine landing. No injuries were reported. A review of the engine history revealed that this was the third "in-flight shutdown" for this engine. The engine's time since new was 21,101.8 hours, its time since overhaul was 2,414.3 hour, and its time installed on the airplane since its last maintenance was 76.4 hours. The reason for the last maintenance was an "in-flight shutdown." The accessory section was examined at the NTSB Materials Laboratory. The report stated that the spur gear appeared undamaged. The spur gearshaft had portions of teeth missing. The housing had markings and impressions consistent with splined spur gear contact. The splined spur gear was found fractured and deformed into an oval shape, resulting in a gap between the mating fracture faces. The outer surfaces parallel to the circumferential plane of the splined spur gear appeared rubbed, and portions had a blue-purple tint consistent with frictional heating. Areas of the fracture surfaces also had a similar blue-purple tint. Portions of five external gear teeth were missing. All of the internal spline's teeth peaks were missing and the teeth were deformed. One radial fracture face had smooth flat features, consistent with fatigue and crack arrest lines were found. The fatigue had multiple origins. Inner diameter origins were located in the root of a spline. The contact surface of the spline tooth adjacent to the fracture origin was deformed consistent with rotational contact with spline crowns. Hardness of the splined spur gear was measured to be 38 HRC, which was within its specified range.

On August 27, 1999, at 1110 central daylight time, a British Aerospace Jetstream 3010, N460CE, operated as Chicago Express flight #3294, piloted by an airline transport pilot rated captain and commercial rated first officer, sustained an in-flight right engine failure and engine shutdown. The flight diverted for an emergency landing at Michiana Regional Transportation Center Airport, near South Bend, Indiana. Visual meteorological conditions prevailed during the 14 CFR Part 121 flight. The 2 flightcrew and 18 passengers on board reported no injuries. The scheduled domestic passenger flight originated at 1025, from Chicago Midway Airport, Chicago, Illinois, and was en route to Kent County International Airport, near Grand Rapids, Michigan, at the time of the incident.

The first officer said, "We leveled off at 9,000 MSL [mean sea level] and had been handed over to South Bend Approach. We had just been given direct Grand Rapids when the right engine abruptly quit. I was flying at the time." He said that he continued to fly as the captain "...ran the appropriate memory items and checklist to shut down and secure the engine." He stated, "We then declared an emergency and briefed the passengers. We requested to land at South Bend, it being the closest airport, and Grand Rapids approx 70 miles away. South Bend vectored us on to final." The first officer said that the captain assumed control and performed a single engine landing.

A Federal Aviation Administration (FAA) inspector examined the accessory section from the right engine, a Garrett TPE 331-10UGR-513H, serial number P63082. The engine history was reviewed. The review revealed that this occurrence was the third "in-flight shutdown" for this engine. The engine's time since new was 21,101.8 hours, its time since overhaul was 2,414.3 hour, and its time installed on the airplane since its last maintenance was 76.4 hours. The reason for the last maintenance was an "in-flight shutdown." The FAA inspector forwarded the accessory section for a detailed examination at the National Transportation Safety Board Materials Laboratory.

The Materials Laboratory Factual Report number 01-071 stated that the spur gearshaft and the spur gear were joined together and rotated freely within the first stage idler housing and that the splined spur gear was received separated from the other components. As assembled in the engine, the splined spur gear is located within the housing and meshes with the spur gearshaft. The report stated, "The spur gear appeared undamaged. Portions of 16 teeth were missing from the spur gearshaft, with not more than four adjacent teeth damaged. Markings and impressions were observed on the interior surface of the housing, consistent with sliding contact with teeth of the splined spur gear." The splined spur gear was found fractured and deformed into an oval shape, resulting in a gap between the mating fracture faces. The report stated, "No pieces appeared to be missing from between the fracture surfaces. The outer surfaces parallel to the circumferential plane of the splined spur gear appeared rubbed, and portions had a blue-purple tint consistent with frictional heating. Areas of the fracture surfaces also had a similar blue-purple tint. Portions of five of the external gear teeth adjacent one of the fracture surfaces were missing. The peaks on all of the internal spline teeth were missing, and the teeth were deformed circumferentially." One face of the radial fracture had smooth flat features, consistent with fatigue, across most of its surface. The report stated, "Crack arrest lines were visible, and at higher magnification using scanning electron microscopy, striations were observed." The fatigue features were reported to have emanated from multiple origins at the splined inner edge. The fracture origins at the inner diameter were located in the root of a spline adjacent to a spline tooth base. The report stated, "The contact surface of the spline tooth adjacent to the fracture origin was deformed consistent with rotational contact with spline crowns on an externally splined shaft (not received by the materials laboratory). According to the engineering drawings for the splined spur gear, the internal splines were flat root, side fit, involute splines. A view of the profile of several of the deformed splines is shown in figure 5 on a cross section through the gear. The root of one of the splines is shown at higher magnification in the center photograph. Cracks were observed in several of the spline roots, including the magnified root shown in figure 5. The cracks were located at both of the root corners adjacent to the bases of the spline teeth. Some of the cracks had secondary cracks, such as the one shown in figure 5. The surface roughness measured from the profile at 80 times magnification was approximately 125 microinches in the root, as specified in the engineering drawings. No fillet was observed at the base of the tooth where it intersected the root, and none was specified in the engineering drawings. According to Machinery's Handbook, 22nd Edition, 'the fillet which joins the sides to the bottom of the tooth space, if generated, has a varying radius of curvature. Specification of this fillet is usually not required. It is controlled by the form diameter which is the diameter at the deepest point of the desired true involute form.'" Hardness of the splined spur gear was measured to be 38 HRC, which was within its specified range. (See appended report.)