LAX93LA338

The propeller separated from the left engine after experiencing a propeller blade separation from its hub assembly. The pilot landed, gear-up, in an open area. A metallurgical examination on the separated propeller blade revealed fatigue cracking of its retention screw. The retention screw was the subject of two service bulletins which were issued by the manufacturer on October 23, 1981, and August 27, 1982. These bulletins required replacement of the older retention screws with the newer retention screws at the next overhaul. The recommended overhaul time for this propeller assembly is five calendar years or 2,000 hours, whichever comes first. The engine log book revealed the last recorded propeller overhaul was performed on January 5, 1978.

On August 29, 1993, at 0953 hours mountain standard time, a Beech 95, N9CE, collided with a barbed wire fence during an emergency landing near Kingman Airport, Kingman, Arizona. The forced landing was precipitated by the loss of a propeller blade and subsequent in flight loss of the left engine. The pilot was conducting a visual rules personal flight to Goodyear Airport, Goodyear, Arizona. The airplane, registered to the pilot's brother, sustained substantial damage. The certificated commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed. The flight originated at Kingman Airport at 0951 hours.

According to the enclosed Pilot/Operator Report, NTSB Form 6120.1/2, the pilot stated that the airplane had arrived from Goodyear Airport, Phoenix, Arizona, earlier that morning with no apparent problems. The pilot reported that he had departed runway 21 and had retracted the landing gear when he heard "a loud bang and shaking." He said he looked at the left engine and noticed that the cowling was loose and realized the left engine had "some sort of catastrophic failure." The pilot said he pitched the aircraft down to maintain airspeed. He reported that the airplane was yawing and turning to the left and estimated his altitude to be "approximately 200 feet above ground level." The pilot reduced power on the right engine to control the yaw and planned to land "gear up" straight ahead. After the landing, he turned off all the switches and fuel valves and exited the airplane. The owner of the airplane and the pilot examined the airplane after the forced landing was made. The examination revealed that the left engine was missing from the "firewall forward."

Additionally, the airplane was examined by an Airframe and Powerplant mechanic located in Kingman, Arizona, under the direction of the Federal Aviation Administration, Scottsdale Flight Standards District Office. The Airworthiness Safety Inspector reported that the propeller blade separated outboard of the clamp on the left engine. Subsequently, the left engine broke loose from the mount and separated. (See the enclosed inspection report for additional details.)

The propeller hub assembly and inboard portion of the blade was submitted to the NTSB Materials Laboratory Division in Washington, D.C., for examination. According to the NTSB Materials Laboratory Division report dated January 10, 1994, examination of the fracture surfaces on separated components revealed no evidence of pre-existing cracking, such as fatigue or stress corrosion cracking. All fractures of these components were typical of overstress separations.

The No. 1 propeller blade had separated through the retainer radius at the inboard end allowing the blade to depart from the hub. Additionally, the examination disclosed that the clamp screw/bolt (Hartzell Propeller, Inc., refers to affected part as a "bolt") on the trailing edge side of the clamp was broken in both clamp assemblies. The threaded portions of both of these broken screws were retained inside the screw holes.

Examination of the fracture face of the recovered blade, serial number D21937, revealed fractures typical of fatigue cracking over approximately 60 percent of the blade cross section. A fatigue crack arrest pattern emanated from an origin area indicated by bracket "01" in figure 2. This origin area was located in the blade retention radius at the position corresponding to the trailing edge of the blade.

Examination of the separated inner clamp screws disclosed that the screws were first manufacturered in 1952, in accordance with part number A-282 drawing and were "bronze" colored. In 1982, the part number A-282 drawing was replaced with a part number A-321 drawing. These screws were color coded "green." Remnants of bronze color were visible on the head of the separated screw, indicating that the screw was the original part number A-282 screw.

According to the attached report, examination of the fracture face revealed features typical of fatigue cracking over about 90 percent of the screw fractured cross section. The fatigue cracking emanated from multiple origins located at the root of a thread. The plane of the fatigue fracture zone was relatively flat and smooth, typical of high cycle fatigue cracking under bending loads. Further examination of the screws with the aid of the stereomicroscope disclosed that both screws had extensive fatigue cracks that emanated from the thread roots.

On October 23, 1981, and August 27, 1982, Hartzell Propeller, Inc., issued service bulletins number 130 and 137, respectively, which indicated that in all steel-hub propellers installed on reciprocating engines, the "bronze" color coded A-282 inner clamp bolts should be replaced with the "green" color coded A-321 screws. The recommended overhaul time from the manufacturer is 5 calendar years or 2,000 hours, whichever occurs first.

According to the engine log book, the last propeller overhaul on the accident airplane was performed on January 5, 1978. (See section 9 for further information.)