N3156VCessna 150M · 1974

On June 11, 2024, about 1250 mountain standard time, a Cessna 150M airplane, N3156V, was substantially damaged when it was involved in an accident near Roll, Arizona. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that she departed Yuma International Airport (NYL), Yuma, Arizona, with a full load of fuel. At approximately 5,500 ft, the engine made a loud bang followed by a total loss of power. She attempted to restart the engine but was not successful and then began to look for a suitable place to land. The pilot stated that by the time she located a nearby private airport, she was parallel to the runway. She turned toward the south, and as she turned back toward the runway, she realized she would not be able to make it and initiated an off-airport landing in a field. During the landing sequence, the airplane struck trees, which resulted in substantial damage to both wings.

Postaccident examination of the engine revealed that only partial rotation of the engine was possible; therefore, the cylinders and pistons were removed from the crankcase. The internal crankcase surfaces and internal engine components were undamaged and were covered in a light oil residue except for the cylinder No. 2 intake valve head, which was embedded in the No. 2 piston head. The intake valve head had separated from its stem near the radius at the head and its stem was found in the carburetor throat. The separation surfaces on the valve head and stem were jagged in appearance. The No. 2 piston was cracked in half. The No. 2 exhaust valve was removed from the cylinder and examination of the valve stem revealed pitting corrosion about 1 inch from the head. The No. 2 cylinder assembly including the valves, pushrods, and piston, as well as the intake and exhaust valves from the Nos. 1, 3 and 4 cylinders, were shipped to the National Transportation Safety Board’s Materials Laboratory for further examination.

The engine had accrued 3,182.5 hours of time since new and 846.7 hours of time since overhaul. According to the maintenance logbooks for the airplane, the engine was overhauled in February 2017, when new Superior (part number SA10200-A20P) cylinders were installed. More than 75 percent of the engine time in service since the overhaul were accumulated after February 2022.

The intake valve for the No. 2 cylinder was fractured at the neck (where the stem met the head) and the stem was bent. The piston had impact marks consistent with contact from the intake valve head and stem, and cracks emanated from the valve head impact area. The piston rings were fractured in the area where the piston was cracked. Intake valve impact damage was also observed on the internal surfaces of the cylinder head, and the inboard end of the intake valve. The No. 2 pushrods were both rolled on a flat table, and each rod rolled smoothly with no gaps, consistent with straight rods.

The external surfaces of the cylinder head had a uniform yellow-gray color and showed no external evidence of tinting from high temperature exposure. However, the rocker box had black flaky deposits of coked oil, particularly around the exhaust valve guide. One valve inner spring and one valve outer spring were also covered with coked oil deposits, and coked oil deposits covered the exhaust valve spring seat.

Both rocker arms had a drive screw at the pushrod end of the rocker arm consistent with an oil channel between the pushrod and the rocker bushing. However, neither of the rocker arms had a drive screw or an oil orifice for valve stem lubrication at the rocker pad end. The Continental Aerospace Technologies Standard Practice Maintenance Manual (SPMM) includes a section titled “Rocker Arm Identification,” that shows differences between the intake and exhaust rocker arm part numbers 639614 and 639615, respectively, that are installed on Continental O-200-series engines. Both rocker arms have oil channels with drive screws at the pushrod end, but the part number 639615 exhaust rocker arm also has an oil channel with a drive screw and orifice at the rocker pad end. According to the SPMM, the distinction is important: “Installing rocker arms in the incorrect position may cause oil starvation to the valve train and/or shorten cylinder life.”

A closer view of the No. 2 intake valve, valve seat, and keeper halves, revealed that one of the keeper halves was loosely held within the valve spring seat and could not be separated from the seat when manipulated by hand. The inside diameters of both intake keeper halves were severely worn, and the locking tab that retained the intake valve in place was missing on both halves. The outside diameter surfaces were also worn, and corresponding wear was observed on the inside diameter of the valve spring seat. Additionally, the inboard edges of the intake keeper halves were deformed outboard, a deformation that contributed to trapping one of the keeper halves within the valve spring seat.

The valve stem had a dark tint extending up to 2.5 inches from the head end face. Substantial pitting damage was observed on the stem between 1.5 inches and 2.2 inches from the head end face. The valve seat contact area had a predominantly black, glazed appearance. The contact area for the valve seat appeared uneven around the circumference. Isolated areas of dark gray deposits and radially oriented streaks were also observed on the valve seat contact area around the circumference.

On the intake valves from cylinders Nos. 1, 3, and 4, the tip end faces generally had a smooth, worn appearance with circular wear patterns. Isolated pits with rounded edges were also observed on each of the tip end faces. Remnants of linear grinding marks consistent with marks from the original manufacture were observed at the outer edge of the tip end face on valves Nos. 1 and 3. Each of the intake valves from cylinders Nos. 1, 3, and 4 had circumferential gouges and adjacent linear scrape marks near the tip end of the valve stem. Thick black deposits were observed on the stem side of the head on each of the intake valves from cylinders Nos. 1, 3, and 4. Flattened deposits were also observed on the valve seat contact surfaces on each valve.

On the exhaust valves from cylinders Nos. 1, 3, and 4, the tip end faces generally had a smooth, worn appearance with a circular wear pattern. Isolated pits with rounded edges were also observed. Coked oil was observed between the stem shoulder and the tip end face on each of the exhaust valves from cylinders Nos. 1, 3, and 4. The keeper lock contact areas on the outboard sides of the keeper grooves were slightly worn on each of the exhaust valves. Dark tinting was observed on the Nos. 1, 3, and 4 exhaust valve stems extending up to 2 inches. Pitted areas were observed within the dark tinted areas on each of the exhaust valves.

The Nos. 1, 3, and 4 exhaust valve seat contact faces all had a black glazed appearance. Isolated areas of dark gray deposits and radially oriented streaks were also observed around the circumference on each of the exhaust valve seat contact areas. The inside and outside diameters of the No. 2 intake valve were measured to be within the specified range. Additionally, the No. 2 intake valve stem-to-guide clearance was less than the corresponding service maximum value.