Accident Details
On August 13, 2017, about 1700 eastern daylight time, a Piper J3C-65, registration N98550, operated by Berkshire Aviation Enterprises Inc., was substantially damaged during a forced landing into trees following a total loss of engine power in cruise flight near Salisbury, Connecticut. The flight instructor and student pilot sustained minor injuries. The local instructional flight was conducted under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and a visual flight rules flight plan was filed. The flight departed Walter J Koladza Airport (GBR), Great Barrington, Massachusetts, about 1640.
The flight instructor reported providing an introductory flight to the student pilot. About 20 miles south of GBR at 2,800 feet mean sea level, the airplane experienced a total loss of engine power. The instructor took control, positioned carburetor heat on, verified fuel selector on and magneto switch to both, but the engine did not regain power. With no suitable landing areas nearby, the instructor performed a slow landing into treetops. The airplane collided with trees and came to rest nose-down entangled.
Engine and Maintenance History
The airplane was equipped with a Continental Motors C90-8F, 90-horsepower engine. Its most recent annual inspection occurred on July 13, 2017, at which time the airframe had 2,093 hours. Engine logbook review showed that maintenance records prior to 1994 were lost; a new logbook was created in June 1994, indicating the engine was overhauled at about 1,300 hours total time. In October 2013, at 689 hours since major overhaul, the engine was disassembled and inspected after a previous accident (NTSB ID # ERA11LA379). During that work, the crankshaft was replaced per the Continental Overhaul Manual dated 1-1994. The engine had accrued about 317 hours from that replacement to the most recent annual inspection.
Post-Accident Examination
A Federal Aviation Administration inspector examined the wreckage and found substantial damage to wings and fuselage. Hand rotation of the crankshaft revealed no thumb compression on two cylinders and no continuity to the rear accessory section.
A teardown examination at the manufacturer's facility under NTSB supervision revealed that the crankshaft gear screws were fractured and the gear had separated from the crankshaft. Fretting was observed near two of four crankshaft screw holes, corresponding to two elongated screw holes on the gear. The gear had an oil stain witness mark aligned with a dowel pin hole on the crankshaft; however, no dowel pin was present as specified in the latest manufacturer illustrated parts catalog (IPC) and overhaul manual (OM). Additionally, the crankshaft gear lacked a dowel pin hole, consistent with a C65 engine gear rather than a C90 gear. The manufacturer's most recent IPC and OM (August 2011) contained instructions to use a gear with a dowel pin hole and align it with a dowel pin to pilot the gear on the crankshaft.