Urbana, IN, USA
N8910M
BEECH 35 B33
The pilot reported that, while in cruise flight, he noticed a change in the engine sound and a 100-rpm increase on the tachometer. He adjusted the propeller control to lower the rpm, but the rpm immediately increased to over 3,500, which is above the red line. The pilot reduced the propeller and throttle controls, but the propeller continued to overspeed. The propeller then separated from the airplane, and engine oil covered the windscreen. The pilot subsequently made a forced landing to a soft bean field, which resulted in substantial damage to the fuselage, wings, and engine mounts. A postaccident examination of the engine revealed that the crankshaft was fractured forward of the No. 6 rod journal across the oil transfer collar area and that the No. 6 rod had separated from the crankshaft. An examination of the fracture revealed evidence of several overheating events at the surface of the crankshaft next to the oil transfer collar hole. A crack had formed adjacent to the overheated surface, and the surface crack led to a stress crack, which formed the surface of the main separation fracture.
HISTORY OF FLIGHTOn September 24, 2013, about 0920 eastern daylight time, a Beech 35-BE33 Debonair airplane, N8910M, conducted a forced landing in a field near Urbana, Indiana. The pilot received minor injuries, the first passenger received serious injuries, and the second passenger was uninjured. The airplane sustained substantial damage. The airplane was registered to and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which operated without a flight plan, but received flight following services from air traffic control. The flight originated from the Washington Municipal Airport (KAWG), Washington, Iowa, about 0730 and was destined for the Van Wert County Airport (KVNW), Van Wert, Ohio. In a statement provided by the pilot, the airplane's engine began to malfunction while enroute to the destination. He noticed a change in the engine sound and the tachometer indicated above 3,500 RPM, which is above the red line. He reduced the propeller and throttle controls, but the propeller continued to over speed. The propeller then separated from the airplane. The pilot declared an emergency and searched for a landing location when oil covered the wind screen and side windows. He conducted a forced landing into a bean field. PERSONNEL INFORMATIONThe pilot, age 62, held a private pilot certificate with ratings for single engine land airplane. He was issued a third class medical certificate on May 10, 2012, with limitations to wear corrective lenses. His most recent flight review was completed in the accident airplane on May 28, 2012. According to the pilot, he had accumulated 1,348 total flight hours and 126 hours in the make and model of the accident airplane. AIRCRAFT INFORMATIONThe Beechcraft 35-BE33 Debonair airplane, serial number CD-690, was a single engine, low-wing, retractable tricycle landing gear, which was manufactured in 1963. The airplane was powered by a Continental Motors IO-470N engine, which drove a three bladed McCauley propeller. On October 10, 2008, the engine received a D-Shannon engine upgrade, Supplemental Type Certificate (STC) #SA5527SW. This upgraded the engine to the Continental IO-470N engine with the McCauley propeller. On March 21, 2009, the propeller was removed, repaired and reinstalled. On August 10, 2010, all cylinders were removed, de-glazed and reinstalled. On August 13, 2009, a complete top overhaul was completed at a tachometer time of 2,158. On November 21, 2012, an annual inspection was completed on the airframe, engine and propeller with no anomalies noted. METEOROLOGICAL INFORMATIONAt, 0935 the weather reported at Warsaw Municipal Airport (KASW), which was 24 miles north of the accident site, reported wind 120 at 4 knots, visibility 10 miles, sky clear, temperature 50 degrees Fahrenheit (F), dew point 45 degrees F, and altimeter setting 30.12 inches of mercury. AIRPORT INFORMATIONThe Beechcraft 35-BE33 Debonair airplane, serial number CD-690, was a single engine, low-wing, retractable tricycle landing gear, which was manufactured in 1963. The airplane was powered by a Continental Motors IO-470N engine, which drove a three bladed McCauley propeller. On October 10, 2008, the engine received a D-Shannon engine upgrade, Supplemental Type Certificate (STC) #SA5527SW. This upgraded the engine to the Continental IO-470N engine with the McCauley propeller. On March 21, 2009, the propeller was removed, repaired and reinstalled. On August 10, 2010, all cylinders were removed, de-glazed and reinstalled. On August 13, 2009, a complete top overhaul was completed at a tachometer time of 2,158. On November 21, 2012, an annual inspection was completed on the airframe, engine and propeller with no anomalies noted. WRECKAGE AND IMPACT INFORMATIONThe airplane landed upright in an open bean field. The engine compartment was displaced to the left. The wings were slightly bent aft and wrinkled and the leading edges sustained damage during the landing. The propeller was located by a land owner two months after the accident. The propeller was shipped to the engine manufacturer to be examined with the engine. ADDITIONAL INFORMATIONThe engine was shipped to Continental Motors for further examination and testing. The examination, which was observed by the NTSB investigator-in-charge, revealed that the crankshaft was fractured forward of the number six rod journal across the oil transfer collar area. All rod journals exhibited oil starvation signatures. The number six rod had released from the crankshaft. The forward portion of the crankshaft and flange remained attached to the propeller. The crankshaft cluster gear was intact and exhibited normal operating signatures. The gear bolts were tight and safety wired and the gear teeth were undamaged. The crankshaft main bearing journals were intact, undamaged and exhibited normal operating signatures. The counterweight assemblies were intact and had unrestricted movement on the hanger blades. The crankcase exhibited exterior damage concentrated at the nose and the area above the number six cylinder. Further examination of the crankshaft revealed that the fracture surface had considerable corrosion. The fracture surface was cleaned with a strong alkaline mixture and most of the rust was removed, which revealed a fatigue fracture surface indicated by beach marks. There was subsurface growth of the crack which emanates from an area below the surface, and was a secondary crack from the first crack that originated from the surface perpendicular to the axis. The crankshaft was sectioned near the initiation area. The cross section revealed several overheating events at the surface between the fracture surface and oil transfer hole. The presence of white untempered martensite indicates temperatures at the surface in excess of 1,400 degrees F. The overlapping heat affected zones indicate several heating events.
The failure of the crankshaft following several overheating events that had led to a stress crack and the subsequent fracture forward of the No. 6 rod journal.
Source: NTSB Aviation Accident Database
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