Pine Bluff, AR, USA
N3101S
AYRES S2R600
After the airplane sustained a complete loss of engine power during initial climb, the pilot performed an off-airport landing. Postaccident examination revealed that three teeth in the torque sensor spur gear separated after four of the five torque sensor mounting bolts became loose. The loose bolts caused the torque sensor housing to move radially away from the gear case, causing the teeth to overload and separate. Subsequently, the engine’s fuel pump and fuel control were no longer driven by the gears in the gear train, which were normally driven by the torque sensor spur gear, thus the engine was starved of fuel. Metallurgical examination showed that the bolts became loose because a bolt that was undersized and of the incorrect configuration had been installed. A maintenance record showed that the engine had previously been disassembled due to a torque sensor failure and an overhauled torque sensor had been reinstalled.
On July 6, 2011, about 1030 central daylight time, an Ayres S2R600 G6, single engine airplane, N3101S, was substantially damaged when it impacted terrain following a complete loss of engine power during initial climb near Pine Bluff, Arkansas. The airplane was owned and operated by Swan Lake Flying Service, Inc. The pilot reported no injuries. Visual meteorological conditions prevailed and a flight plan had been not filed for the 14 Code of Federal Regulations Part 137 agricultural flight. At the time of the accident the airplane was departing from Ladd Airstrip, Pine Bluff, Arkansas, for a local flight. The pilot reported that his take-off and initial climb were normal. He had started a turn and was about 150 feet above ground level when the engine suddenly quit producing power. The pilot performed a forced landing near the end of the runway, impacted terrain and a drainage ditch, and came to rest upright. The impact resulted in substantial damage to the engine mounts and forward fuselage and both main landing gear partially separated from the airplane. Airframe and engine maintenance logbooks were not available for examination. One maintenance record from a repair facility showed that the engine from the airplane had been disassembled and repaired three years previously following a torque sensor failure. The record showed that the torque sensor and several other parts had been installed in the engine in an overhauled condition. The repaired engine was approved for a return to service on September 13, 2008, and was reinstalled on the airplane A postaccident examination of the engine disclosed that four of five torque sensor assembly mounting bolts were loose. One of the loose bolts holding the torque sensor was undersized, of the incorrect configuration, and was not the part specified. The torque sensor in the engine was the same serial numbered part listed in the September 13, 2008, maintenance record. Heavy wear was observed on the torque sensor housing around two bolt holes and the mounting hardware that corresponded with the two holes was also worn. The difference in bolt shank diameter displayed motion of the torque sensor housing relative to the gear case as evidenced by the separation of anti-rotation tabs which left deep wear grooves in the torque sensor housing and were indicative of tab contact. Three teeth were found separated from the torque sensor spur gear. The torque sensor spur gear is part of an assembly that drives the fuel pump and fuel control. Metallurgical examination showed that the failure mode of the separated teeth exhibited distinct features indicative of high cycle fatigue initiation and tip loading of the gear teeth after the torque sensor mounting bolts became loose. According to the manufacturer, when the engine fuel pump and fuel control are no longer driven by the gears in the gear train, which are driven by the torque sensor spur gear, the engine will stop running.
The use of an incorrect mounting bolt by maintenance persons to attach the engine torque sensor, which resulted in an internal failure of the torque sensor and subsequent loss of engine power due to fuel starvation.
Source: NTSB Aviation Accident Database
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