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N77MN accident description

Oregon map... Oregon list
Crash location 43.166389°N, 119.484166°W
Nearest city Alkali Lake, OR
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Tail number N77MN
Accident date 26 Jun 2011
Aircraft type Christen Industries Inc Pitts S-1T
Additional details: None

NTSB Factual Report

On June 26, 2011, about 1015 Pacific daylight time, a Christian Industries Inc. Pitts S-1T, N77MN, sustained substantial damage during a forced landing following a partial loss of engine power about 26 miles northeast of Alkali Lake, Oregon. The airplane was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. The commercial pilot, the sole occupant of the airplane, sustained minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the personal flight. The cross-country flight originated from Burns, Oregon, about 0950 with an intended destination of Lakeview, Oregon.

The pilot reported that during cruise flight at 6,500 feet mean sea level (msl), a large amount of oil suddenly coated the windscreen. The pilot turned away from the edge of a plateau and noticed that the engine oil pressure gauge indicated "0." The pilot stated that during the off airport landing, she attempted to pull the nose up and drag the tail on the ground to slow the airplane, but had no response from the elevator or ailerons. Subsequently, the airplane impacted the ground in a nose-low attitude and cart wheeled before it came to rest upright.

Examination of the airplane by the pilot revealed that the upper and lower right wings were folded upwards and the fuselage exhibited structural damage. The wreckage was recovered to a secure location for further examination.

Examination of the recovered Lycoming AEIO-360-A1E engine, serial number L-24247-51A, revealed that a heavy amount of visible oil and oil covered dirt was observed surrounding the forward portion of the engine and engine cowling. All engine accessories remained attached to the engine crankcase and accessory case. All cylinders remained secure to the engine crankcase. The propeller remained attached to the crankshaft propeller flange. All oil line fittings were found tight and secure.

The propeller and top spark plugs were removed. The crankcase front bearing oil seal was partially extruded from the crankcase nose seal bore. The crankshaft was rotated by hand at the crankshaft propeller flange. Rotational continuity was established throughout the engine and valve train. Thumb compression and suction was obtained on all four cylinders.

The front bearing oil seal was removed from the crankshaft and examined. The spring was found intact and undamaged. A slight amount of sealant type material was found around the circumference of the forward portion of the seal. The hose extending from the crankcase breather fitting was removed. Compressed air was applied to the end of the removed hose and air was felt expelling from the crankcase breather fitting and the crankcase nose seal bore area. The reason for the front bearing oil seal to become extruded from the crankcase bore area was undetermined.

Review of the airplanes maintenance logbooks revealed that the front bearing oil seal was replaced on September 14, 2010, at a tachometer time of 1,845.4 hours and replaced again on June 8, 2011, at a tachometer time of 1,910.2 hours. At the time of the accident, the airplane had accumulated 10.1 hours since the front bearing oil seal was replaced.


NTSB Probable Cause

The loss of engine oil during cruise flight due to the failure of the front bearing oil seal.

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