Incident Details
At 1658 Pacific daylight time on June 30, 2008, a Cessna TR182, registration N7XZ, made a forced landing in an open field near Bend, Oregon, resulting in substantial damage. The aircraft, registered to Spirit Flight Inc. (doing business as Wings of the Cascades) and operating under contract with the United States Forest Service, was on a local fire reconnaissance flight under 14 CFR Part 135 and visual flight rules. Visual meteorological conditions prevailed. The pilot, an airline transport pilot, sustained serious injuries; the sole passenger received minor injuries. The flight had departed Roberts Field Airport (RDM) in Redmond, Oregon, at approximately 1543, intending to fly to Prineville, Oregon.
According to a written statement from the pilot, during cruise flight the engine began to run rough, the propeller rpm exceeded the redline, and oil splattered onto the windscreen. The pilot intended to return to Redmond or Bend but could not, so she initiated an off-airport landing in an open field. As the airplane approached the field, oil continued to coat the windscreen, originating from the cowling aft of the propeller, making forward visibility nearly impossible. Before landing, the pilot turned the fuel selector to OFF and set 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.
Local law enforcement examination revealed the right wing was buckled, the engine firewall bent, and oil on the windscreen. The airplane was recovered for further examination.
Engine Examination
On October 15, 2008, at Specialty Aircraft Services in Redmond, Oregon, a representative from Textron Lycoming Engines, under the supervision of the NTSB investigator-in-charge, examined the Lycoming O-540-L3C5D engine (serial number L-21341-40A). The engine remained attached to the airframe via all mounts, and all accessories were still attached to the crankcase. Disassembly and visual inspection revealed the crankshaft (serial number V7379) was intact but exhibited a crack approximately 380 to 400 degrees around the circumference of the forward bearing journal, radiating outward from the oil-through hole. Both forward main bearings were severely worn through the babbitt layer, exposing the copper layer, and the forwardmost connecting rod bearing also showed wear through the babbitt layer. No other anomalies were noted.
The crankshaft, crankcase halves, and forward main bearings were sent to the NTSB Materials Laboratory for further examination.
Crankshaft Analysis
NTSB Materials Laboratory examination of the crankshaft revealed a spiral crack originating from the oil through-hole at the forward bearing journal. Initial crack faces extended 2 mm along a right-hand spiral at a 9-degree rise to the transverse plane, then changed to a left-hand spiral at a 45-degree rise for 20 mm clockwise and 40 mm counter-clockwise (viewed from aft to forward). The crack then changed to a right-hand spiral at a 45-degree rise that continued around the journal perimeter until terminating opposite the origin.
Scanning electron microscopy of the intact oil through-hole end showed multiple short cracks emanating from both sides. The fracture origin was consistent with a brittle intergranular fracture through the nitride layer. Multiple crack arrest marks were present on the left-hand spiral segment, indicating the fracture began at the oil through-hole. The marks ended where the spiral changed from left-hand to right-hand. The right-hand spiral fracture surface was on a slant plane consistent with overstress separation. The crankshaft's chemical composition was within manufacturer's specifications.
Maintenance History
According to the owner/operator, the engine was removed from the airframe in mid to late 2005 for an overhaul due to time approaching recommended limits. Two separate A&P mechanics partially overhauled it over several months, then a third mechanic completed the overhaul in April 2006. Logbook records show the 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 tach time 813.3 hours. The most recent annual inspection was on May 30, 2008, at tach time 1,065.6 hours (252.3 hours since major overhaul).
A service tag from Engine Components Incorporated (ECI), San Antonio, Texas, dated November 10, 2004, indicated the crankshaft (serial V7379, part LW17626) was repaired per MPP-9045 and found within new limits. A work order stated the main bearing journals were polished and the propeller flange slightly ground; the crankshaft passed magnaflux inspection with no anomalies.