NTSB Factual Report

On November 24, 2016, about 0850 mountain standard time, a Cessna 182A airplane, N6077B, was substantially damaged during a forced landing following a loss of engine power near Safford, Arizona. The commercial pilot and the 3 passengers were not injured. The airplane was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal cross-country flight. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from the Safford Regional Airport (SAD) at 0815, with an intended destination of Holbrook, Arizona.

The pilot reported that during cruise flight at 8,500 ft mean sea level, he noticed that the oil pressure began to fluctuate and he decided to return to the airport. When the airplane was about 4 miles north of SAD, the engine lost power and he initiated a forced landing to an area of open desert. During the landing roll, the airplane struck two dirt berms and the nose wheel collapsed.

Post-accident examination of the airplane by a Federal Aviation Administration inspector revealed that the forward portion of the fuselage structure was substantially damaged.

Examination of the engine was conducted on July 13, 2017, under the supervision of the National Transportation Safety Board investigator-in-charge. All engine accessories with the exception of the carburetor, which was removed from the engine prior to shipment, remained attached. Two holes in the crankcase above the number 5 and 6 cylinders were observed. Silicone was observed around the crankshaft nose seal.

The crankcase exhibited normal operational signatures mostly throughout with the exception of mechanical damage surrounding the number 5 and 6 cylinder bays. Crankcase main bearings #1, #2, and #4 exhibited normal operational signatures. The #3 main bearing exhibited wear into the copper layer.

The camshaft exhibited mechanical damage to the cylinder 5 and 6 lobes. The number 5 crankshaft connecting rod bearing journal exhibited thermal discoloration along with mechanical damage. The number 6 crankshaft connecting rod bearing journal exhibited slight mechanical damage. The remainder of the crankshaft exhibited normal operational signatures.

During disassembly of the engine, cylinders 1, 2, 3, and 4 exhibited normal operational signatures. However, cylinder number 5 exhibited mechanical damage to the cylinder skirt. The piston remained inside the cylinder with mechanical damage to the piston skirt. The piston pin was separated from the piston and the connecting rod.

Cylinder number 6 exhibited mechanical damage to the cylinder skirt. The piston remained inside the cylinder and exhibited mechanical damage. The connecting rod remained attached to the piston via the piston pin. The connecting rod cap was separated as well as part of the lower portion of the cap. The remaining portion of the rod cap was connected to the yoke. The bolt was missing, and the bolt hole appeared elongated.

The remains of the number 5 and 6 pistons, rings, piston pins, and connecting rods were sent to the NTSB Materials Laboratory and subsequently examined by a Material Research Engineer.

The cylinder number 5 pistons, rings, piston pin, connecting rod, and bearings revealed that they all exhibited damage significant enough to deform the outer surfaces. All of this damage was found consistent with post-fracture damage while the engine was still running. The pieces of the number 5 connecting rod exhibited severe batter and deformation. The bushing and bearing pieces were damaged and folded onto themselves.

The connecting rod bolts were both fractured at midlength, consistent with where the faces of the connecting rod cap and connecting rod mate. Both bolts exhibited necking adjacent to their fracture surfaces. The fracture surfaces were generally oriented 90° toward the bolt length and exhibited a rough texture and dull luster, consistent with tensile overstress fractures. The most notable feature on pin side bore of the connecting rod was the fracture at the neck yoke of the rod web. A portion of the pin bore wall was sectioned away to observe the fracture surfaces and exhibited deformation consistent with having been twisted about the piston pin. The inner bore surfaces exhibited circumferential scoring marks.

The three portions of the connecting rod cap had fractured in two places, and the previously curved cap had been deformed outward in an almost flat orientation. The fracture surfaces, along with the other surfaces of the cap, exhibited severe post-fracture damage in the form of batter, gouging, and scraping. The gouging marks on the inside bearing surface were consistent with either the cap being bounced around after fracture/separation or having an adjacent object impressed into the cap.

Both endcaps of the piston pin had fractured away, but only one of the cap remnants were found. The mating fracture surfaces of the pin and pin endcap fragment had been extensively damaged, consistent with post-fracture impact. No discernible information could be obtained from examination of the fracture surfaces.

The majority of damage to the piston was present on the underside of the part to the skirt flanges. The crown or head of the piston facing the cylinder interior exhibited some combustion deposits, but there were no features consistent with severe wear, impact, or thermal damage. The underside of the piston exhibited small gouge and batter marks, consistent with impact with multiple metallic pieces. The lower portions of the piston, including those surrounding the piston pin boss, had fractured into multiple pieces. All of the fracture surfaces examined exhibited features consistent with overstress failure of aluminum castings—rough and tortuous surfaces, dull luster, and no indications of pre-existing cracks or discontinuities. Examination of the chevron marks and river patterns on the piston fracture surfaces revealed that they were consistent with fracture beginning from the inside of the piston. Many of the fracture features were consistent with having emanated from the piston pin boss.

The components from the number 6 cylinder exhibited damage significant enough to deform the outer surfaces. This damage was less than those observed on the components of the number 5 cylinder. The damage observed was consistent with post-fracture damage while the engine was still running.

The number 6 connecting rod components had been damaged with batter and other post-fracture damage, but the degree of damage was less than that of the components of the number 5 connecting rod. The bolts from the connecting rod were fractured at midlength, consistent with where the rod and cap mate. The areas on the bolts adjacent to their fracture surfaces thinned down or necked. The fracture surfaces themselves exhibited a 45° slant, consistent with tensile overstress.

The crankshaft side of the connecting rod had fractured near the yoke neck. The pin side of the rod arm was relatively undamaged. The bushing was still present inside the pin bore of the rod. The inner bearing surface of the connecting rod that had faced a crankshaft journal surface exhibited some wear marks, consistent with sliding in a lateral direction. In addition, some material smearing outward of the bearing surface was present. The fracture surface of the rod arm was generally dull in luster, with post-fracture iron oxide (rust) corrosion and smearing damage on the outer regions of the fracture surface. Examination of the undamaged portions of the fracture surface using an SEM revealed dimple rupture, consistent with overstress.

For further information, see the Materials Laboratory Factual Report within the public docket for this accident.

Review of the engine logbooks revealed that the engine was overhauled on May 20, 1996, at a tachometer time of 3,686 hours. The most recent 100-hour/annual inspection was completed on October 19, 2016, at an engine time since overhaul of 1,556.9 hours.

NTSB Probable Cause

The total loss of engine power due to the failure of the No. 5 piston, piston pin, or connecting rod assembly for reasons that could not be determined due to the severity of the post fracture damage.