BULLHEAD CITY, AZ, USA
N6698A
CESSNA 172
The aircraft was in cruise flight at 7,500 feet when the pilot heard five loud bangs after which the engine seized. The pilot attempted an emergency landing in a farm field and collided with rough terrain and a fence. Examination of the maintenance records revealed that the engine had been in service for about 35 years and had been majored twice during 2,000 total operating hours. The most recent major overhaul occurred 13 years and 344 hours prior to the accident. Internal examination of the engine disclosed that the crankshaft had failed in fatigue at the number two main journal. Detailed metallurgical examination revealed that the number one bearing insert had been mispositioned during assembly of the crankcase causing a localized oil flow restriction to the main bearings and an eventual fatigue failure of the crankshaft.
On April 25, 1993, at 1740 Mountain standard time, a Cessna 172, N6698A, collided with a fence and rough terrain during a forced landing near Bullhead City, Arizona, following a total loss of power. Neither the private pilot nor his passengers was injured. The airplane sustained substantial damage during the off airport landing. No flight plan was filed for the personal cross country flight which had originated at Overton, Nevada, on the day of the accident. Post crash examination of the engine revealed that the crankshaft had failed between cylinder numbers three and four. The airplane had been modified in accordance with a supplemental type certificate to replace the original installation Continental 0-300 engine with a Lycoming 0-340-A1A 170 horsepower engine and a controllable pitch propeller. ENGINE INFORMATION According to records available, the engine was shipped new from the Lycoming factory to Doyn Aircraft on January 15, 1958, and put into service on or about March 8, 1958. Log book entries revealed that on October 1, 1968, a major overhaul was completed on the engine at a total time in service of about 1,386 hours. On May 13, 1980, a major overhaul was again completed. At the time of the second overhaul, the engine had accrued about 468 hours in the 13 hears since the last major overhaul. The total time on the engine was calculated at 1,854 hours. At the time of the accident on April 25, 1993, the records indicate about 344 hours had accumulated on the second major overhaul for a total time of about 2,000 hours over a period of about 35 years. TESTS AND RESEARCH The failed crankshaft and bearing inserts were sent to the National Transportation Safety Board's Office of Research and Engineering, Materials Laboratory Division, for detailed metallurgical examination. Examination of the crankshaft revealed that it had failed at the aft side of the number two bearing support journal. The number one main bearing inserts were found to have impression marks from the two bearing locator dowel pins located in the crankcase. Signatures located on the bearing inserts indicated that they were out of their designed position and partially obstructing an oil port. A copy of the National Transportation Safety Board's Metallurgist's factual report is attached.
a fatigue failure of the crankshaft due to improper assembly of the engine during the major overhaul.
Source: NTSB Aviation Accident Database
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