Incident Summary
On June 8, 2022, at about 1100 central daylight time, a Beech 58 airplane, registration N78KL, sustained minor damage during an incident near Evansville, Indiana. The pilot and four passengers were not injured. The flight was operated as a personal flight under Title 14 Code of Federal Regulations Part 91.
According to the pilot, no anomalies were noted during the preflight inspection. The airplane departed from Kirk Field Airport (PGR) in Paragould, Arkansas, with a destination of James M. Cox Dayton International Airport (DAY) in Dayton, Ohio. About one hour into the flight, while at an altitude of approximately 9,000 ft mean sea level and an airspeed of about 180 knots, the pilot heard a “boom” noise. The airframe began vibrating and the airplane yawed to the left. The pilot contacted approach control, reported the need for an immediate landing, and was directed to divert to Evansville Regional Airport (EVV) in Evansville, Indiana.
The pilot reduced power on the right engine and maneuvered the airplane for landing on runway 18 at EVV. The landing was completed without incident. After exiting the airplane, the pilot observed that one aluminum propeller blade on the left engine had separated at about mid-span. The separated blade segment was not recovered. No other damage was noted on the propeller, engine, or airframe.
Aircraft and Propeller Information
The airplane was equipped with two Hartzell Propeller model HC-C4YF-2E/FC7063Q propellers, each featuring four blades. These propellers were installed under Federal Aviation Administration (FAA) Supplemental Type Certificate SA1762SO on November 12, 2002. The fractured blade was manufactured on September 6, 2000.
Maintenance History
Airplane registration records show that the airplane was sold on May 13, 2021. The previous 100-hour inspection, completed before the sale, occurred on December 17, 2020, at which time the propeller had accumulated 1,097 hours of time since overhaul (TSO). The most recent 100-hour inspection of the propeller took place on January 10, 2022, when the propeller had accumulated 1,172 hours TSO. At the time of the incident, the propeller had accumulated 1,200 hours TSO.
The mechanic who performed the most recent 100-hour inspection reported a visual examination of the blades and recalled observing only normal damage, such as small nicks, which he dressed. He did not recall performing any paint work on the blades.
Examination of Fractured Blade
The fractured blade (design number FC7063Q, serial number J51843) was removed from the hub and sent to the National Transportation Safety Board Materials Laboratory for examination. The fracture surface showed signatures consistent with high-cycle fatigue failure. The blade fractured approximately 16.9 inches from the blade butt. The deice boot was severed at the fracture and partially debonded on both the camber and face sides.
The fatigue origin area coincided with an area of damage covered with a thick black paint that had a slightly different composition than the thinner paint on the rest of the blade. No evidence of a repair was found in this area. The pilot reported no knowledge of paint work on the blades or previous propeller blade impacts.
Regulatory Guidance
FAA Advisory Circular 20-37E, Aircraft Propeller Maintenance, discusses propeller blade failures and notes that propellers are highly stressed components subjected to centrifugal forces, bending, and vibratory loads. It states that damage such as nicks, scratches, or corrosion can create stress concentrations leading to crack formation and eventual blade failure.
FAA Special Airworthiness Bulletin NE-08-22, Propeller Search Inspection (General Visual Inspection), addresses cosmetic repairs, emphasizing that an exposed defect can be inspected while a hidden defect cannot, and that cosmetic repairs creating hidden defects are unacceptable.