What happened
On May 16, 2012, a Beechcraft 95-A55, registration PT-WKY, was performing a private flight from Boa Vista, RR, to Flores, AM, carrying a pilot and five passengers. Approximately one hour and 45 minutes into the flight, the pilot reported hearing a loud bang, followed by significant vibrations and a change in the rotation of the left propeller.
Upon recognizing the failure, the pilot shut down the affected engine and attempted to manually feather the left propeller. However, the propeller failed to respond, resulting in increased drag. Unable to maintain the assigned altitude, the pilot executed an emergency landing on the BR-1t4 highway near KM 163 in Presidente Figueredo, AM. During the landing, the aircraft struck a road sign, causing light damage to the left landing light, the left wing's upper skin, and the left aileron. All six occupants emerged from the aircraft uninjured.
The investigation
CENIPA investigators examined the left McCauley propeller and discovered that one of the propeller blades could be moved freely by hand. Subsequent disassembly revealed that the actuator pin for one of the blades had fractured, causing the total loss of propeller pitch control.
Detailed metallurgical analysis of the fractured pin revealed that the component was not an aeronautical-grade part. While a new, certified pin was composed of martensitic stainless steel with high hardness (380 HV), the fractured pin was made of common carbon steel (192 HV) and lacked a protective surface coating. The investigation also identified that a long-standing Service Bulletin (No. 99, issued in 1972) regarding the replacement or rework of these specific actuator pins had not been implemented.
Additionally, the investigation found that the aircraft was significantly overweight at takeoff. The calculated takeoff weight was 2,565kg, exceeding the maximum takeoff weight of 2,213kg by approximately 352kg. Although fuel burn had reduced the excess weight by the time the failure occurred, the aircraft was still approximately 204kg over its limit during the incident.
Findings
- The failure of the propeller was caused by the fracture of an uncertified, non-aeronautical grade actuator pin due to fatigue.
- The aircraft was operated in an overweight condition at takeoff.
- Maintenance records for the airframe, engine, and propeller were not up to date.
- The pilot, while qualified for the flight type, lacked experience on the specific route flown.