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N7XZ accident description

Oregon map... Oregon list
Crash location 44.094444°N, 121.200000°W
Nearest city Bend, OR
44.058173°N, 121.315310°W
6.2 miles away
Tail number N7XZ
Accident date 30 Jun 2008
Aircraft type Cessna TR182
Additional details: None

NTSB Factual Report

On June 30, 2008, at 1658 Pacific daylight time, a Cessna TR182, N7XZ, was substantially damaged during a forced landing near Bend, Oregon. The airplane was registered to and operated by Spirit Flight Inc. doing business as Wings of the Cascades, Redmond, Oregon, under contract with the United States Forest Service. The local fire reconnaissance flight was operated under the provisions of 14 Code of Federal Regulations (CFR) Part 135 and visual flight rules (VFR) with a company flight plan in effect. Visual meteorological conditions prevailed. The airline transport pilot sustained serious injuries and the sole passenger sustained minor injuries. The cross-country flight departed from the Roberts Field Airport (RDM), Redmond, Oregon, about 1543 with an intended destination of Prineville, Oregon.

In a written statement, the pilot reported that during cruise flight, the engine began to run rough as she noticed the propeller revolutions per minute (RPM) was beyond the redline indication and oil began to splatter on the windscreen. The pilot intended to return to Redmond or Bend, Oregon, however, was unable to do so and initiated an off airport landing in an open field near her position. As the airplane approached the field, oil continued to coat the left and right sides of the windscreen. The pilot stated that the oil was originating from the cowling aft of the propeller and made "forward visibility nearly impossible." Prior to landing in the field, the pilot turned the fuel selector to the OFF position and positioned the mixture to idle cut-off. During the landing roll, the airplane struck a barbwire fence and came to rest upright on a two-lane highway.

Examination of the airplane by local law enforcement revealed that the right wing was buckled throughout, the engine firewall was bent, and oil was observed on the windscreen. The airplane was recovered to a secure location for further examination.

On October 15, 2008, at the facilities of Specialty Aircraft Services, Redmond, Oregon, the engine was examined by a representative from Textron Lycoming Engines under the supervision of the Safety Board investigator-in-charge (IIC).

Examination of the Lycoming O-540-L3C5D engine, serial number L-21341-40A, revealed that it remained attached to the airframe via all engine mounts. All of the engine accessories remained attached to the engine crankcase. The engine was disassembled and visually inspected. The crankshaft, serial number V7379, was found intact; however, exhibited a crack about 380 to 400 degrees around the circumference of the forward bearing journal that radiated outwards from the oil-through hole. Both forward main bearings were found severely worn through the babbitt layer, exposing the copper layer of the bearings. The first or forward most connecting rod bearing also exhibited wearing through the babbitt layer. No further anomalies were noted with the engine. The crankshaft, left and right crankcase halves, and forward main bearings were sent to the NTSB Office of Research and Engineering, Materials Laboratory Division for further examination.

Examination of the crankshaft by an NTSB Materials Engineer revealed that the spiral crack originated from the oil through-hole at the forward bearing journal. The crack faces on either side of the oil through-hole extended for 2 millimeters (mm) along a right-hand spiral at a 9 degree rise to the transverse plane. The crack path then changed to a left-hand spiral direction at a 45 degree rise to the transverse plane. The left hand spiral extended for 20 mm in the clockwise direction and 40 mm in the counter-clockwise direction (as seen looking from aft to forward). The crack then changed to a right hand spiral at a 45 degree rise that continued around the perimeter of the journal before terminating on the opposite side of the cracks origin.

Scanning electron microscopy (SEM) of the intact end of the oil through-hole revealed multiple short cracks emanating from either side of the undamaged oil through-hole end. The origin of the fracture was found to be consistent with a brittle intergranular fracture through the nitride layer.

Examination of the fracture surface revealed multiple crack arrest marks on the left-hand spiral segment of the fracture surface. The shape and orientation of the marks indicated that the fracture originated at the oil through-hole. The crack arrest marks terminated at the point where the spiral path changed from a left-handed to right-handed spiral. The fracture surface on the right-handed spiral surface was on a slant plane consistent with overstress separation. The chemical composition of the crankshaft was tested and found to be within the manufacturer's specified limits. (Refer to the attached Materials Laboratory Factual Report.)

According to the owner/operator of the airplane, the engine was removed from the airframe in mid to late 2005 to undergo an engine overhaul. This was due to the engine total time since overhaul approaching the manufacturer's recommended time limits. The engine was initially disassembled and partially overhauled over the course of a few months by two separate airframe and powerplant (A&P) mechanics. It then remained disassembled and in storage until about April, 2006, when a third A&P mechanic completed the overhaul.

Review of aircraft logbook records revealed that an engine overhaul was completed on May 1, 2006, at an engine total time of 3,521 hours. The engine was installed on the airframe on May 15, 2006, at a tach time of 813.3 hours. The most recent annual inspection of the engine and airframe was conducted on May 30, 2008, at a tach time of 1,065.6 hours, 252.3 hours since engine underwent a major overhaul.

A service tag from Engine Components Incorporated (ECI) of San Antonio, Texas, dated November 10, 2004, indicated that the crankshaft, serial number V7379, part number LW17626 was repaired in accordance with MPP-9045 and was found within "new limits." According to a work order obtained from ECI regarding the crankshaft, the main bearing journals were polished and the propeller flange was slightly ground. The crankshaft underwent a magnaflux inspection and no anomalies were noted.

NTSB Probable Cause

The failure of the crankshaft during cruise flight due to fatigue.

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