Sugar Grove, IL, USA
N471BB
RAYTHEON AIRCRAFT COMPANY B36TC
The pilot reported that shortly after takeoff, the airplane’s engine lost partial power and shook violently. The pilot elected to land the airplane in a cornfield off the end of the runway, where the it sustained substantial damage to both wings. A postaccident engine run performed with the engine still mounted on the airframe revealed no anomalies, but full-power testing could not be performed due to shortening of the propeller blades to facilitate the test. A mechanic who performed work on the engine after the accident reported that the turbocharger was full of oil and that the shaft appeared to be loose. As a result, the turbocharger was replaced with an overhauled unit. The mechanic also reported that the mechanical fuel pump was replaced after the accident but prior to arrival at the engine repair facility. It was reportedly replaced to correct a lean mixture condition, but the mechanic could not verify the reason. Based on the available information, the reason for the engine's partial loss of power could not be determined during the course of the investigation.
On July 25, 2012, about 0850 central daylight time, a Raytheon Aircraft Company model B36TC airplane, N471BB, collided with a corn crop and the ground just after takeoff from runway 36 at the Aurora Municipal Airport (ARR), Sugar Grove, Illinois. The pilot and passenger were not injured. The airplane received substantial damage to both wings. The aircraft was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal 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 and its intended destination was the Wittman Regional Airport, Oshkosh, Wisconsin. A postcrash examination of the airplane's wings revealed leading edge wing skin and substructure damage along the entire spans. The pilot reported that he had arrived at ARR two days prior to the accident flight and had filled the fuel tanks at that time from the airport’s self-service fuel pumps. He reported that on the day of the accident, he performed a pre-flight examination of the airplane and found no anomalies. The examination included sampling of the fuel sumps which revealed clear samples that were free of debris. The pilot stated that the weight and balance calculations placed the airplane near full gross weight, but within the operating envelope. The pilot elected to depart using runway 36 which was the nearest runway to the fixed base operator where he had parked the airplane. The pilot said that the weather reports indicated that using runway 36 would result in a 5 to 7 knot quartering tailwind, but calculations he had performed indicated that the takeoff roll would require about 1,500 feet of runway given those conditions. The pilot reported that the ensuing takeoff roll required about one-half of the 3,198 foot runway and that after retracting the landing gear, the engine sputtered and shook violently. The pilot estimated that the airplane was between 50 and 100 feet above the ground at this point. He elected to land the airplane in the corn crop directly ahead of the airplane with the landing gear retracted. Subsequent to the accident, the NTSB investigator-in-charge (IIC), along with a representative from the Federal Aviation Administration performed an engine test run at ARR with the engine still mounted on the airplane. Damage to the propeller blades required that the blades be cut about 18 inches outboard of the propeller hub. In addition, the airframe was secured to prevent movement during the test. The NTSB IIC operated the engine from the pilot seat using the normal engine controls. The start-up was performed using the procedure found within the Pilot’s Operating Handbook. The engine started without hesitation and idled normally. The engine speed was increased, but due to the shortened blades it was necessary for the NTSB IIC to limit throttle movement as to prevent exceeding the maximum allowable engine speed. During the test, all gauge readings were normal and no defects were noted in operation. Although the test did not show any anomalous indications in engine operation, full power testing could not be performed due to the shortened propeller blades. The pilot noted in his report that during repair operations, the facility performing the engine repairs found “a significant and suspicious” quantity of oil on the turbocharger. Discussions with the mechanic at the repair facility revealed that the turbocharger was replaced after the accident with an overhauled unit due to excess oil in the turbocharger and an apparent looseness in the shaft. The mechanic also stated that prior to arrival at the engine repair facility; the engine’s mechanical fuel pump had been replaced reportedly due to fluctuations that prevented proper mixture adjustment of the fuel system. The mechanic could not verify this anomaly because the replacement of the fuel pump occurred after the accident and prior to its arrival at the engine repair facility. During testing at the repair facility, the engine did not exhibit this anomalous behavior, but the new fuel pump had already been installed at that time.
The partial loss of engine power for reasons that could not be determined because postaccident testing and examination did not reveal any anomalies that would have precluded normal operation.
Source: NTSB Aviation Accident Database
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