NTSB Factual Report

HISTORY OF FLIGHT

On April 14, 2013, about 1020 Pacific daylight time, an Engineering and Research Corporation (Ercoupe) 415-C, N87114, landed hard during a forced landing shortly after takeoff from Mesquite Airport, Mesquite, Nevada. The pilot was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. The private pilot sustained minor injuries; the airplane sustained substantial damage to the right wing and firewall during the accident sequence. The cross-country personal flight departed Mesquite 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 an engine speed of 2,300 rpm. About 5 minutes later, he felt a low frequency vibration, and assuming it was an engine speed related harmonic, reached forward to adjust the throttle. Just as he reached forward, 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. In an attempt to diagnose the problem, he advanced the throttle again, and the engine surged to 4,200 rpm. The pilot realized that the propeller had separated from the engine, and began to configure the airplane for a forced landing.

He stated that due to the altered center of gravity with the propeller missing, he was unable to maintain positive airplane control at any airspeed below 85 mph. He subsequently performed a forced landing into rocky desert scrub, about 5 miles from the airport.

The airplane had undergone an annual inspection on August 6, 2012, at a tachometer time of 264.2 hours. Maintenance records indicated that at the time of inspection, 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 the installation of the crankshaft oil seal at a tachometer time of 252.3 hours. The tachometer on the airplane at the accident site indicated 294.5 hours.

The crankshaft was of the tapered type, with the propeller hub and flange assembly being held in place with a single hub nut. The tapered portion of the crankshaft was keyed to accept the propeller hub assembly. The crankshaft tip, propeller hub, and hub nut all contained four "safety holes" drilled 90 degrees apart radially. The design was such that a flat-head pin was installed through one of these holes once they were aligned, after the correct hub nut torque was applied. A cotter pin was utilized to retain the flat-head pin. According to representatives from Continental Motors, once the correct hub nut torque was applied, the flat-head and cotter pins should be loose within the assembly, a tight fit indicating that the propeller hub nut had backed off.

Neither the propeller nor its associated hub hardware forward of the crankshaft seal was recovered. The crankshaft was removed from the engine to facilitate 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, with the fourth exhibiting elongation in the plane of rotation, and material smear of 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.

NTSB Probable Cause

Separation of the propeller from the engine during initial climb due to the incorrect torque applied to the propeller hub nut during maintenance.