DEN07LA083

According to the pilot, shortly after departing runway 18 she heard what "sounded like a loud backfire, a single bang," and then the engine lost power. The pilot selected a nearby field and performed a forced landing. During the landing the nose gear collapsed resulting in substantial damage. An examination of the engine revealed that the crankshaft gear separated from the crankshaft and was loose inside the accessory case. The upper portions of five of the six screws used to secure the gear to the crankshaft were found in the accessory case. Metallurgical examination of the fracture surface revealed signatures consistent with fatigue fractures. One screw was sectioned and tested for hardness with the results of 29, 30, 30, and 31 Rockwell C Harness (HRC). According to TCM, the drawing specifies an H5 fastener with a hardness requirement of 32 through 37 HRC. In addition, the head of the screw had a diameter of .40 inches or less. The TCM drawing specifies a diameter of .44 inches. According to TCM, this could have resulted in inadequate torque for this installation. An examination of the airplane flight controls and engine controls revealed no anomalies.

On April 9, 2007, approximately 1330 central daylight time, a Beech 35, N460B, piloted by a commercial pilot, sustained substantial damage when it impacted terrain during a forced landing near Topeka, Kansas. Visual meteorological conditions prevailed at the time of the accident. The personal flight was being conducted under the provisions of Title 14 CFR Part 91 without a flight plan. The pilot sustained minor injuries and the passenger reported no injuries. The cross-country flight had just departed the Philip Billard Municipal Airport (TOP), Topeka, and was en route to Kansas City, Missouri.

According to a statement submitted by the pilot, the engine start, taxi, and takeoff were normal, without issue or incident. The pilot reported that shortly after departing runway 18 (4,331 feet by 75 feet, asphalt) she heard what "sounded like a loud backfire, a single bang," and then the engine lost power. The pilot selected a nearby field and performed a forced landing. During the landing the nose gear collapsed.

An examination of the airplane, conducted by two airworthiness inspectors with the Federal Aviation Administration (FAA), Wichita, Kansas, revealed that the firewall was wrinkled, and the fuselage skin on the right side was crushed upward. The "keel structure" in the engine compartment was bent. FAA confirmed the existence of fuel in the left and right fuel tanks. The FAA reported that a 1/4 teaspoon of particulate matter and a teaspoon of rust water was sumped from the left and right fuel tanks, respectively. An examination of the airplane flight controls and engine controls revealed no anomalies.

The engine, a Teledyne Continental Motors (TCM) E185-8, was removed from the airframe and sent to TCM in Mobile, Alabama, for further examination. The engine was examined by the Safety Board Investigator-in-Charge and TCM investigators on July 17, 2007. Examination of the engine revealed the crankshaft gear separated from the crankshaft and was loose inside the accessory case. The upper portions of five of the six screws, used to secure the gear to the crankshaft, were found in the accessory case. Safety wire remained attached to two of the five screw heads.

Examination of the gear and crankshaft-mounting surface revealed fretting. Portions of all six screws remained inside the crankshaft. Examination revealed the screws, used to mount the gear to the crankshaft, were allen wrench, capscrew style head screws. According to TCM, the drawing calls for a common hex head screw. The crankshaft gear, screws, and dowel were sent to the TCM Metallurgical Lab for further analysis.

Metallurgical examination of the fracture surface revealed signatures consistent with fatigue fractures. One screw was sectioned and tested for hardness with the results of 29, 30, 30, and 31 Rockwell C Harness (HRC). According to TCM, the drawing specifies an H5 fastener with a hardness requirement of 32 through 37 HRC. In addition, the head of the screw had a diameter of .40 inches or less. The TCM drawing specifies a diameter of .44 inches. According to TCM, this could have resulted in inadequate torque for this installation.

According to the engine maintenance records, the last engine overhaul was completed on August 13, 1970, in Akron, Ohio, at an airframe total time of 2,425.5 hours. The last annual inspection was performed on September 2, 2006, at an engine total time of 671.5 hours.