Investigation of In-Flight Shutdown of Turboprop Engine Due to Electrical Discharge Damage
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TECHNICAL ARTICLE—PEER-REVIEWED
Investigation of In-Flight Shutdown of Turboprop Engine Due to Electrical Discharge Damage Bokwon Lee . Gyu-Ho Kim . Ryan L. Karkkainen . Young-Ha Hwang
Submitted: 30 September 2017 / in revised form: 30 December 2017 / Published online: 10 January 2018 Ó ASM International 2018
Abstract A turboprop training aircraft experienced an inflight shutdown failure with complete seizure of its propeller. Disassembly of the mishap engine revealed that many of the engine components were severely damaged. The laboratory investigation of the failed engine components determined that mechanical failure of the driveshaft bearing in the gearbox was the principal contributing factor that led to in-flight complete seizure of the propeller shaft. Microscopic examination of the failed bearing remnants found electrical arc-induced pittings which played a role as crack initiation sites resulting in premature rolling contact fatigue cracking during continued engine operation. The investigation established clear evidence of electrical discharge damage (EDD) on engine components connecting from the starter-generator to the failed input driveshaft bearing. The evidence of EDD observed in multiple elements located along the electrical current path and the residual magnetism measurement suggested that the starter-generator is highly associated with the source of the EDD.
B. Lee (&) ATRI (Aero Technology Research Institute), Ayang-ro, Donggu, Daegu 41052, Republic of Korea e-mail: [email protected] G.-H. Kim Department of Mechanical Engineering, University of Texas at Dallas, 800 W. Campbell, Richardson, TX 75080, USA R. L. Karkkainen Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, FL 33146, USA Y.-H. Hwang Korea Institute of Industrial Technology, 57, Yangho-gil, Yeongcheon-si, Gyeongsangbuk-do 38822, Republic of Korea
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Keywords Electrical discharge damage Turboprop engine Bearing Starter-generator Electrical arc
Introduction A turboprop training aircraft experienced an in-flight engine shutdown during a training mission. The pilot reported white smoke had leaked from the exhaust of the engine along with a loud banging noise and vibration at the moment of the incident. The propeller did not rotate shortly after the loud noise. The pilot correctly identified the engine problem and took appropriate action to return to the base. He successfully completed an emergency landing after 48 km of flight without engine power. The mishap turboprop engine had operated for approximately 3200 h from new installation and 270 h from the last engine overhaul. The mishap engine was disassembled and inspected under supervision of the accident investigation board. The exterior surface of the engine was covered with engine oil with localized burn marks. In addition, a large amount of melted metallic particles were spread out inside of the engine components. Disassembly and laboratory examination determined that engine failure was precipitated by fracture of the input driveshaft
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