Aviation Safety Council （ASC） releases the occurrence investigation report as follows: a Roc Aviation Company BN-2B-20 aircraft returned to Fongnian Airport due to left engine failure. The failure was resulted from number 3 cylinder separated from crankcase and protruded outwards to damage left engine which caused engine cowling burst and deformation.

On April 16, 2015, a Roc Aviation Company, BN-2B-20 aircraft, B-68802, executed a ferry flight mission from Fongnian Airport to Songshan Airport. After took off, the aircraft encountered dual generator warning lights on and left engine failure conditions during climb. The flight crew contacted Kaohsiung Approach and requested radar vector to return to Fongnian Airport for maintenance. Except the instructor pilot and copilot, the flight departed with one additional copilot and one maintenance personnel, totally four people on board. There was no injury to the persons on board.

According to the Republic of China （ROC） Aviation Occurrence Investigation Act, and the content of Annex 13 to the Convention of International Civil Aviation Organization （ICAO）, the ASC, an independent aviation occurrence investigation agency, was responsible for conducting the investigation. The organization or agency been invited to join the investigation team included: Civil Aeronautics Administration of Ministry of Transportation and Communications, Roc Aviation Company, National Transportation Safety Board of the United States of America （NTSB）, Air Accidents Investigation Branch of the United Kingdom （AAIB）, engine manufacturer, Lycoming and aircraft manufacturer, Britten Norman. The Final Report was reviewed and approved by ASC’s 44th Council Meeting on April 26, 2016.

Findings related to probable causes: A post occurrence examination found that 5 out of 8 stud bolt nuts were not at their positions. During engine overhaul, under torque condition might exist when number 3 cylinder was installed. This caused insufficient tightness of number 3 cylinder and crankcase connection. The accumulated flight hours of left engine were more than 1,400 hours. Long term operation of engine and axial movement of piston led to the looseness of stud bolt nuts. Some stud bolt nuts might be separated before the occurrence to produce vibration at the mating surface of number 3 cylinder and crankcase during engine operation. Subsequent bending or fracture of stud bolts thus caused the separation of number 3 cylinder from crankcase and then damaged to left engine.

Findings related to the risks: The flight crew did not follow the procedures of the Aircraft Operation Manual to declare emergency immediately when encountering engine failure. The flight crew did not apply standard callout procedures and accurately express the situation of aircraft and flight crew’s intention to Kaohsiung Approach Control Tower and Fongnian Tower. As a result, controllers could not realize aircraft condition at that time to provide timely assistances.

Aviation Safety Council issued a total of three Safety Recommendations.

To Roc Aviation Company: Enhance the promulgation to flight crew following company’s manuals to declare emergency immediately when encountering engine failure condition.

To Civil Aeronautics Administration: Supervise Roc Aviation Company to enhance the promulgation to flight crew following company’s manuals to declare emergency immediately when encountering engine failure condition.

To Lycoming engine: It is recommended that Lycoming follows the suggestions of Special Airworthiness Information Bulletin NE-14-13 issued by the Federal Aviation Administration to control overhaul quality of 540 series engine.

Full investigation report is available for download at http://www.asc.gov.tw

Sherry Liu, Engineer
Tel: 89127388-330
Email:sherry@asc.gov.tw