N1197
BELL 407
The commercial pilot was conducting an on-demand air taxi commuter flight in the helicopter. The pilot reported that, after the helicopter lifted off of the oil platform and entered a hover, the engine started to lose power. He nosed the helicopter forward to clear the platform, and the low-rotor speed horn sounded and the warning light illuminated. The pilot subsequently inflated the floats, leveled the helicopter, and landed it in the water. After shutting down the engine and securing the main rotor, the passengers and pilot safely exited the helicopter. A postincident engine examination revealed a rupture in the brazed patch area of the outer combustion case (OCC). Metallurgical examination revealed a fatigue crack in the outer skin beneath and extending beyond the perimeter of the patch. The portion of the patch adjacent to the rupture had braze material nearly covering the mesh screen. The braze alloy had also flowed into the crack and covered portions of the fracture surface. The evidence is consistent with the patch being rebrazed after the crack had formed, likely in an attempt to repair the crack. In addition, the braze alloy composition in this area did not conform to the engineering drawing requirement. The engine maintenance manual permitted welding to repair OCC cracking; however, it did not authorize brazing to repair OCC cracking. The maintenance records provided by the operator indicated that cracks had been repaired by welding about 3 years before the incident. The records did not include any subsequent entries related to the OCC, which precluded a determination of when or by whom the unauthorized braze repair had been attempted. Although the OCC was last inspected about 100 hours before the accident, it could not be determined whether the cracking would have been visible or concealed under the repair patch at that time.
On May 30, 2014, about 0945 central daylight time, a Bell Helicopter model 407, N1197, experienced a loss of engine power after lifting off from the Eugene Island 182A oil rig helipad. The pilot deployed the emergency flotation system and safely landed on the Gulf of Mexico. The pilot and five passengers were not injured. The helicopter was not damaged during that landing; however, it subsequently capsized and was substantially damaged during the recovery effort. The helicopter was registered to GM Leasing Company and operated by Westwind Helicopters Inc. under the provisions of 14 Code of Federal Regulations Part 135 as an on-demand air taxi flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The flight was originating at the time of the accident. The intended destination was the Abbeville Chris Crusta Memorial Airport (IYA), Abbeville, Louisiana.The pilot reported that after picking up into a hover, he applied forward cyclic to begin the takeoff. About the time that the helicopter reached the edge of the platform, the engine started to lose power. He nosed the helicopter forward to clear the platform. The low rotor speed horn came on and the warning light illuminated. The pilot inflated the floats, leveled the helicopter, and landed in the water. After shutting down the engine and securing the main rotor, the passengers and pilot safely exited the helicopter. A postincident examination of the engine was performed under direct oversight of a Federal Aviation Administration inspector. Metallurgical examination was performed by the engine manufacturer with final review by a National Transportation Safety Board (NTSB) metallurgist. The engine examination revealed a rupture in the left side brazed patch area of the outer combustion case (OCC). It was located in the sheet metal area between the compressor discharge tube flange and the turbine inlet flange. Subsequent metallurgical examination revealed the presence of a fatigue crack in the outer skin beneath the brazed patch. The crack measured about 2.7 inches in length and extended beyond the perimeter of the brazed patch. The portion of the brazed patch adjacent to the rupture exhibited braze material that nearly covered the mesh patch. In addition, the braze alloy had flowed into the crack and covered portions of the fracture surface. The braze alloy composition in this area did not conform to the engineering drawing requirement. The Engine Control Unit (ECU) was downloaded. The ECU Incident Recorder contained three events. The first was triggered due to a high engine measured gas temperature (MGT). The ECU is designed to automatically limit fuel flow in response to a MGT exceedance. The second event was recorded about 1.5 seconds later due to a low rotor speed (92-percent Nr) event. The recorded data indicated that the rotor speed recovered to 100 percent, consistent with the pilot lowering collective in order to enter an autorotation. However, the rotor speed subsequently decayed below 92-percent triggering a third event. According to the flight and maintenance records provided by the operator, the most recent 150-hour engine inspection was completed on May 6, 2014, at 16,319.5 hours total airframe time and 2,359.5 hours total engine time. A continuous airworthiness inspection and a 300-hour corrosion inspection were completed on May 21, 2014, at total airframe and engine times of 16,389.2 hours and 2,422.7 hours, respectively. On May 27, 2014, the engine did not start before the first flight of the day. Ignition components were subsequently replaced. Later that day, after 4.4 flight hours had elapsed, a turbine bearing oil tube was found to be damaged. It was replaced and a subsequent engine test run revealed no further anomalies. The airframe had accumulated 16,309.7 hours total time and the engine had accumulated 2,449.7 hours total time. At the time of the incident, the airframe and engine had accumulated 16,420.1 hours and 2,460.1 hours, respectively. The maintenance records also included a Transport Canada Authorized Release Certificate related to the OCC. The certificate noted that cracks in the OCC were repaired by welding in February 2012. No other entries or documentation associated with the OCC was included in the maintenance records provided by the operator. The engine manufacturer noted that the brazed patch was incorporated on the OCC in order to provide additional structural support for the component. In March 2013, they issued an Alert Commercial Service Letter to inform operators that cracking had been observed in the OCC. In addition, routine inspection of the OCC was moved from the 300-hour inspection procedure to the 150-hour inspection procedure to provide for a more detailed inspection of the OCC. The engine maintenance manual noted that cracks in the outer shell and the liner inner basket may be repaired by welding. However, the maintenance manual did not include any provision for using brazing repairs for OCC cracking.
The improper repair of the outer combustion case, which led to its ultimate failure due to the continued progression of a fatigue crack and resulted in a partial loss of engine power during takeoff.
Source: NTSB Aviation Accident Database
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