Accident Details
On March 27, 2025, at about 1200 Hawaii-Aleutian standard time, a Piper PA-28-140, registration N261FC, was substantially damaged when it crashed near Royal Kunia, Hawaii. The flight instructor and student pilot reported minor injuries. The airplane was operated under 14 Code of Federal Regulations Part 91 as an instructional flight.
The flight instructor and student pilot departed Honolulu Airport (HNL), Honolulu, Hawaii, for the student's first instructional flight. As the airplane climbed to about 1,500 ft mean sea level, the instructor felt a slight vibration not present on an earlier flight in the same airplane that day. He initiated a climb and turned back toward HNL. Subsequently, a loud bang was heard, the engine lost all power, and the nose dropped.
Emergency Landing
The flight instructor performed an off-airport emergency landing into a field. During landing, the airplane struck several small trees and vegetation, resulting in substantial damage to the fuselage, wings, and empennage.
Propeller Separation and Examination
After landing, the flight instructor noted the propeller was missing. It was later found at a nearby residence; no one at the residence was injured.
Examination of the separated propeller revealed the engine crankshaft had fractured and separated just aft of the crankshaft propeller flange (CPF). The separated CPF, mating flywheel starter ring gear, and six attaching bolts with washers were sent to the NTSB Materials Laboratory for examination.
The laboratory examination determined that the CPF had separated from the crankshaft through the webs between lightening holes at roughly the same radial location. The separation was due to multiple fatigue fractures through the flange webs. Fracture surfaces on two diametrically opposite webs were perpendicular to embedded cylindrical-shaped items consistent with bolt shanks. The fatigue fractures initiated at these bolt pieces in two of the crankshaft propeller flange webs and propagated over a long period.
Maintenance History
Maintenance records indicated that the Lycoming O-320-62A engine and the Sensenich propeller were installed on the airplane on September 15, 2019. Available records did not include any entries noting removal or alteration of the propeller assembly since its initial installation. The most recent annual inspection was completed on February 5, 2025, recording 1,805.1 hours on the engine since overhaul. The most recent 100-hour inspection of the propeller was on March 7, 2025, with about 3,975.6 hours since new.
No record of a crankshaft modification was found, and no part markings were observed on the outer diameter of the propeller flange as specified on the manufacturer's drawing; therefore, the exact age and model of the crankshaft could not be determined. Historical engine records indicating the date and details of the last engine overhaul could not be located.