Aviation Accident Summaries

Aviation Accident Summary LAX06LA048

San Diego, CA, USA

Aircraft #1

N3936D

Cessna 182A

Analysis

The engine experienced a loss of power and the airplane collided with a fence while the pilot was performing a forced landing. As the airplane approached the vicinity of the destination airport, the engine experienced a total loss of power. The pilot made a forced landing on highway about 2 miles from the airport. During the landing roll, the airplane impacted a fence. A post accident examination of the engine revealed that rotation of the crankshaft did not generate rotation of the camshaft. Removal of the starter drive gear assembly revealed that four gear teeth were missing from the camshaft sprocket and one gear tooth was missing from the crankshaft sprocket. The gear teeth were retrieved and sent to the Safety Board Materials Laboratory for examination. The camshaft gear sprocket failed due to fatigue initiating at the root of one of the teeth. Several other teeth had fatigue consistent with secondary initiation due to load shedding from the original failed tooth; the crankshaft gear failure was also secondary. Microstructural examination and hardness testing was performed on a section of a camshaft tooth, which met drawing specifications. A thin layer of decarburization was observed on the surface.

Factual Information

HISTORY OF FLIGHT On November 27, 2005, at 1326 Pacific standard time, a Cessna 182A, N3936D, experienced a loss of engine power and collided with a fence while performing a forced landing on Highway 67 near Gillespie Field, San Diego, California. The private pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The pilot was not injured; the airplane sustained substantial damage. The personal cross-country flight departed Livermore, California, about 1115, with a planned destination of Gillespie Field. Visual meteorological conditions prevailed and a flight plan had not been filed. In both written and verbal statements, the pilot reported that after making contact with the control tower, he configured the airplane for landing at Gillespie Field. As the airplane approached the vicinity of the airport, the engine experienced a total loss of power. The pilot made a forced landing on Highway 67, about 2 miles from the airport. During the landing roll the airplane impacted a fence and its corresponding support pole, incurring damage to the right wing spar. AIRPLANE INFORMATION The Cessna 182A, serial number 34636, was manufactured in 1957. According to the pilot, the airplane had accumulated a total time in service of 2,896 hours. A review of the logbooks revealed that the most recent annual inspection of the airframe and engine was performed on January 01, 2005, corresponding to 76 flight hours prior to the accident. The powerplant, a Teledyne Continental Motors O-470L, serial number 67624, is a six cylinder, air cooled, direct drive, horizontally opposed, normally aspirated (carburetor), internal combustion engine rated at 230 horsepower at 2,600 revolutions per minute (rpm). The maintenance records listed a total time for the engine the same as the airframe, with 2,820 hours at the last annual inspection. The engine accrued 1,145.2 hours since its last major overhaul. The pilot, who additionally held an airframe and powerplant (A&P) certificate with inspection authorization (IA), had signed the logbooks to reflect that he performed all recent maintenance on the accident airplane. TESTS AND RESEARCH An aviation maintenance technician with inspection authorization performed an examination of the engine at the request of a National Transportation Safety Board investigator. Upon removal of all of the spark plugs, he noted no anomalies with the coloration (light gray) or wear signatures. He reinstalled the bottom spark plugs and attempted to obtain thumb compression via rotation of the crankshaft. He noted no compression on cylinders number 1, 4, and 6; he was able to obtain strong compression from remaining cylinders 2, 3, and 5. While rotating the crankshaft, he noted that the camshaft did not appear to rotate. Removal of the starter drive gear assembly revealed that four gear teeth were missing from the camshaft sprocket and one gear tooth was missing from the crankshaft sprocket. He subsequently retrieved the missing gear teeth from the compromised oil pan with the aid of narrow cylindrical magnet. The gear teeth were sent to the Safety Board Materials Laboratory for examination. The fracture surface on the crankshaft gear tooth appeared smooth and rubbed, consistent with an overstress fracture in tension. The tooth contained a contact mark near the center of the inside bend radius. Tension cracks were located along the outside bend radius. The fracture surfaces of two of the camshaft teeth had relatively smooth features with curving arrest lines, consistent with fatigue. One tooth had fatigue features that emanated from an origin area near the aft flank and extended across approximately 95 percent of the fracture. The other tooth's fatigue features extended 70 percent of the fracture, with multiple origins. Microstructural examination and hardness testing was performed on a section of a camshaft tooth, which met drawing specifications. A thin layer of decarburization was observed on the surface.

Probable Cause and Findings

The failure of the camshaft due to fatigue of one of the gear teeth, which resulted in a loss of engine power. Factors were the fence and the fence post.

 

Source: NTSB Aviation Accident Database

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