Accident Overview
On June 12, 2017, at about 0615 eastern daylight time, a Cessna 172M, registration N13306, was substantially damaged during a forced landing to a golf course near Suffolk, New York. The private pilot was not injured. The aircraft was operated under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed and no flight plan was filed. The flight originated from Brookhaven Airport (HWV) in Shirley, New York, and was destined for Bayport Aerodrome (23N) in Bayport, New York.
Pilot Account
According to the pilot, the purpose of the flight was to purchase fuel at HWV and then return to 23N. While en route to 23N, he heard a "loud pop" and the engine experienced a total loss of power. The pilot checked the fuel selector and mixture, then searched for a location to perform a forced landing. He declared an emergency, unsuccessfully attempted to restart the engine, and turned toward a golf course. During the landing, the airplane struck a tree, resulting in substantial damage to the right wing.
Maintenance History
According to Federal Aviation Administration (FAA) airworthiness records, the airplane was manufactured in 1973 and originally equipped with a Lycoming O-320 engine. The most recent engine overhaul was completed on April 9, 2011, as recorded in the maintenance logs. The log entry stated, "Engine assembled and overhauled per Lycoming maintenance manual." It noted that several components, including the crankshaft and crankshaft gear, were overhauled. Airworthiness approval tags (FAA Form 8130-3) for these components noted in the remarks section, "Inspected and/or repaired per Lycoming SB 475 C excluding paragraph 6." The entry did not explicitly state the final crankshaft gear bolt torque, note the installation and bending of the lockplate against the bolt head, or confirm that the inspections and rework required by Lycoming Service Bulletin Number 475C were accomplished. At the time of installation, the engine had accumulated 4,337 total hours.
The most recent 100-hour inspection was performed on June 15, 2016, at which time the engine had 4,520.5 total hours and 183.5 hours since major overhaul. A note in the engine maintenance log dated June 5, 2017, indicated 216.5 hours since major overhaul, with no other remarks.
Post-Accident Examination
Following the accident, the aircraft was recovered to a local maintenance facility. Fuel was plumbed to the engine, but three unsuccessful start attempts were made. The left magneto was removed; rotating the propeller by hand revealed no rotation of the left magneto drive gear. Similarly, the right magneto showed no movement. Further inspection revealed that the crankshaft drive gear was displaced from the aft end of the crankshaft. Disassembly showed that the crankshaft drive gear retention bolt had backed out about 0.25 inch but still had some threads engaged. The lockplate was in place and bent around the bolt.
The dowel pin (part number STD-1065) was measured at 0.245, 0.241, 0.240, and 0.234 inches in remaining portions, all below the minimum diameter of 0.3095 to 0.3100 inches specified in the manufacturer's service bulletin. No thread damage was found on the bolt or the crankshaft counterbore. The bolt was marked "SL GR 8" rather than the required part number 2246 as per the service bulletin.
The crankshaft gear and attaching hardware were examined at the NTSB Materials Laboratory. The alignment dowel exhibited a fatigue fracture with multiple crack origins and arrest marks, consistent with unidirectional bending transitioning to reverse bending. The pilot flange outer diameter showed rubbing damage, and the lockplate tab was bent but not aligned with its plastic hinge.
Findings
Lycoming Service Bulletin No. 475C outlines mandatory procedures for attaching the crankshaft gear during overhaul, including proper torque, seating checks, and the use of a new bolt and lockplate. The bulletin specifies that a logbook entry must document the final bolt torque, verify lockplate bending, and confirm compliance with the bulletin's inspections and rework.