The pilot reported that, while maneuvering the Cessna 180B on floats about 2,500 feet above ground level, he heard a “slight squeal” coming from the engine before it started to sputter.
After the plane had descended to about 1,500 feet, the engine and propeller “completely stopped.”
The pilot determined that the plane would not reach a nearby lake and chose an unpaved road in the woods near Piscataquis County, Maine, for the forced landing.
The right wing hit a tree about 60 feet above the ground, and the plane then hit the road, which resulted in substantial damage to the wings, fuselage, and empennage.
Examination of the engine revealed that the crankshaft could be rotated freely by hand, and removal of the oil sump revealed piston material and the No. 3 exhaust valve head, which was fractured at the stem below the head.
Disassembly of the engine revealed normal wear and appearance on all of the cylinders except for the No. 3 cylinder, piston, and exhaust valve.
Metallurgical examination of the No. 3 exhaust valve revealed that the fracture had initiated at the outer surface of the valve stem and that the valve had fractured due to fatigue at the transition of the stem to the valve.
The NTSB determined the probable cause as the fatigue fracture of the No. 3 exhaust valve, which initiated at the outer surface of the valve stem and resulted in the subsequent total loss of engine power over terrain unsuitable for landing.
NTSB Identification: ERA14LA446
This September 2014 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.