Eden Prairie, MN, USA
N20FP
BEECH 95
The pilot stated that he had no recollection of the events leading up to the accident. The passenger reported that the airplanes' engines seemed to come up to full power during takeoff. The airplane lifted off about halfway down the runway; however, it didn't climb very well. The stall warning sounded just as the airplane was off the end of the runway, and the pilot's efforts to continue flight were unsuccessful. The right wing dropped, and the airplane descended and impacted the ground. A witness reported that the airplane's nose was pitched up 10 to 15 degrees and the wings appeared to be level, as it was flying in ground effect about 10 feet agl. He noted that the engines seemed to be running without any obvious problems. A postaccident examination revealed a lack of compression on the right engine No. 4 cylinder. Further investigation determined that the intake valve spring on the cylinder had fractured. Metallurgical examination noted that the fracture surfaces exhibited features indicative of fatigue progression initiated by corrosion pitting. Corrosion pits and red rust deposits were observed on many areas of the spring. The fatigue initiation also coincided with longitudinal tooling marks consistent with the original forming of the spring. Maintenance records indicated the right engine had been overhauled nearly 2 years prior to the accident. The cylinders were replaced with new non-original equipment manufacturer (OEM) assemblies at that time. The replacement cylinder assemblies were furnished with the valves and valve springs installed. According to the pilot, the right engine had accumulated 18 hours since overhaul.
On April 1, 2010, about 1440 central daylight time, a Beech model 95, N20FP, impacted a flooded ravine about 2 miles south of Flying Cloud Airport (FCM), near Eden Prairie, Minnesota. The flight had departed from Runway 18 (2,691 feet by 75 feet, asphalt) at FCM. The pilot and passenger both sustained serious injuries. The airplane was registered to Fisher Air LLC, and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91, as a repositioning flight after avionics maintenance. Visual meteorological conditions prevailed for the flight, which was not operating on a flight plan. The flight was originating at the time of the accident. The pilot reported that the purpose of the flight was to reposition the airplane from FCM to New Richmond Regional Airport (RNH), New Richmond, Wisconsin, after avionics work has been completed. He stated that he had no recollection of the events leading up to the accident. The passenger stated that the engines seemed to come up to full power during takeoff. The airplane lifted off about halfway down the runway; however, it didn't climb very well. The stall warning sounded just off the end of the runway about 50 feet above ground level (agl). The pilot appeared to check the gear position and auxiliary fuel pump in an attempt to troubleshoot the problem. The pilot reduced the pitch attitude in an attempt to increase airspeed, but the airplane was unable to maintain altitude. The right wing dropped, and the airplane descended from an altitude of about 300 feet agl. It came to rest in a flooded area at the bottom of the hill off the end of the runway. A witness reported that the accident airplane's nose was pitched up about 10 to 15 degrees. The wings appeared to be level and it was flying in ground effect about 10 feet agl. He noted that the engines seemed to be running, and he did not recall hearing any sputtering or seeing any smoke. A hill dropped off past the end of the runway. The airplane came to rest upright about 30 yards out into a flooded area. The wings were facing north and the fuselage was canted about 30 degrees relative to the wings. The nose section was separated from the remainder of the fuselage and the windshield was broken out. There did appear to be fuel present at the accident site. Examination of the right engine revealed a lack of compression on the #4 cylinder. Further investigation determined that the #4 cylinder intake valve spring was fractured into 5 pieces. Metallurgical examination noted that some of the spring fracture surfaces had been damaged due to mechanical contact. However, the undamaged fracture surfaces exhibited features indicative of fatigue progression. Fatigue initiation was located at corrosion pits on the surface of the spring. Similar corrosion pits and red rust deposits were observed on many areas of the spring. The fatigue initiation also coincided with longitudinal tooling marks consistent with the original forming of the spring. The accident airplane was a 1958 Beech model 95 (s/n TD-14). The airplane was powered by 2 Lycoming O-360-A1A engines, each capable of developing 180 horsepower. According to the maintenance logs, an annual inspection was completed on October 15, 2009, at 7,078.1 hours total airframe time. The left engine (s/n L515-36) was overhauled in July 1990. The right engine (s/n L2076-36) was overhauled in June 2008. The logs indicated that at the time of the annual inspection, the left and right engines had accumulated 1,837.0 hours and 2.1 hours since overhaul, respectively. On the NTSB accident report, the pilot noted that the left and right engines had accumulated 1,940 hours and 18 hours since overhaul, respectively. A flight log, entitled "Fisher Air – N20FP," was provided to the NTSB with the aircraft documentation. The log included flight times dated January 7, 2010, through April 1, 2010; the date of the accident. The flight time noted in that log totaled 14.1 hours.
The fatigue failure of an intake valve spring on the right engine, which resulted in a partial loss of engine power on takeoff.
Source: NTSB Aviation Accident Database
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