Cessna 172 Engine Failure Due to Missing Crankshaft Components (N5255R)

What happened

The pilot was operating a Cessna 172 aircraft while climbing through the airspace. The flight was proceeding normally until the aircraft reached an altitude of approximately 1500 feet above ground level. At this point, the engine suffered a sudden and complete failure. Unable to maintain altitude or continue the climb, the pilot initiated an emergency descent.

The pilot selected a suitable area for an off-airport landing. The aircraft impacted small trees and brush during the approach. The impact resulted in significant damage to the airframe and the engine compartment. There were no reports of injuries to the occupants at this time.

The investigation

Following the accident, investigators conducted a thorough examination of the aircraft's powerplant. The inspection focused on the engine's internal components to determine the root cause of the sudden power loss. Mechanics disassembled the engine and inspected the crankshaft assembly.

The examination revealed critical mechanical anomalies within the crankcase. Specifically, the crankshaft dowel pin was found to be sheared off. Furthermore, the crankshaft gear bolt and its associated lock plate were missing entirely. These components are essential for securing the crankshaft gear in place.

Findings

The physical evidence pointed directly to a manufacturing or maintenance error during the engine's last overhaul. The absence of the crankshaft gear bolt and lock plate suggests these parts were likely not installed during the previous maintenance event. Without these fasteners, the crankshaft gear was free to move under operational stress.

The sheared dowel pin indicates that excessive vibration or misalignment occurred prior to the failure. This mechanical instability led to the catastrophic disintegration of the internal components. The loss of drive to the propeller resulted in the immediate engine failure experienced by the pilot. The primary cause was inadequate maintenance during the previous overhaul, specifically the failure to install required hardware.