History of Flight
On April 14, 2013, at about 1020 Pacific daylight time, an Engineering and Research Corporation Ercoupe 415-C, registration N87114, experienced a propeller separation during initial climb and subsequently executed a forced landing into rocky desert scrub near Mesquite Airport, Mesquite, Nevada. The private pilot, operating under 14 CFR Part 91, sustained minor injuries. The airplane sustained substantial damage to the right wing and firewall. The cross-country personal flight departed Mesquite at about 1015, with a planned destination of Ely Airport, Ely, Nevada. Visual meteorological conditions prevailed, and a visual flight rules flight plan had been filed.
The pilot reported that the ground run-up, takeoff, and initial climb were uneventful, with the airplane maintaining a climb rate of 500 feet per minute at 2,300 rpm. About 5 minutes after departure, he felt a low-frequency vibration. Assuming it was an engine speed related harmonic, he reached forward to adjust the throttle. As he did so, the engine speed surged to 4,000 rpm, and he immediately retarded the throttle. The pilot could not see any propeller movement, and the engine did not appear to be producing thrust. Advancing the throttle again caused the engine to surge to 4,200 rpm. The pilot then realized that the propeller had separated and configured the airplane for a forced landing. Due to the altered center of gravity with the propeller missing, he was unable to maintain positive control at airspeeds below 85 mph. He subsequently performed a forced landing about 5 miles from the airport.
Aircraft and Engine Information
The airplane had undergone an annual inspection on August 6, 2012, at a tachometer time of 264.2 hours. Maintenance records showed that the Continental C85-12 engine, serial number 27027-7-12, had accrued 320.2 hours since overhaul in July 1996. An entry dated July 27, 2012, indicated that the propeller was removed to facilitate installation of the crankshaft oil seal at a tachometer time of 252.3 hours. The tachometer at the accident site indicated 294.5 hours.
The crankshaft was of the tapered type, with the propeller hub and flange assembly held in place by a single hub nut. The tapered portion was keyed to accept the propeller hub assembly. The crankshaft tip, propeller hub, and hub nut each contained four safety holes drilled 90 degrees apart radially. The design called for a flat-head pin installed through one of these holes once aligned after correct hub nut torque, retained by a cotter pin. According to Continental Motors representatives, after correct torque application, the flat-head and cotter pins should be loose within the assembly; a tight fit indicated that the hub nut had backed off.
Examination Findings
Neither the propeller nor its associated hub hardware forward of the crankshaft seal was recovered. The crankshaft was removed for inspection. Its threaded portion exhibited flattening and peening damage to about 45 percent of its surface. Three of the four safety holes were round and appeared undamaged, while the fourth showed elongation in the plane of rotation and material smear on its outer lip.
The owner stated that the crankshaft oil seal was replaced due to an oil leak. He did not recall seeing a cotter pin ever installed on the hub nut, noting instead the use of a cadmium-plated bolt and Nyloc nut.