What happened
On June 2, 2016, a CAP-4 aircraft, registration PP-HIY, departed from Bacacheri Airport (SBBI) for a scenic flight over the Curitiba metropolitan area. The flight was being conducted under visual flight rules (VFR) with a pilot and one passenger on board. During the flight, a loud noise was heard within the cabin, immediately followed by a loss of engine power.
In response to the engine failure, the pilot executed standard emergency procedures and notified the Bacacheri Tower. The pilot then performed an emergency landing in an unprepared field in the municipality of Campo Magro, Paraná. Upon exiting the aircraft, the pilot discovered that the propeller had detached from the engine during flight. The aircraft sustained damage to the propeller, engine, and engine cowling, but both occupants were uninjured.
The investigation
The CENIPA investigation focused on the mechanical failure that led to the propeller separation. While the engine, a Continental C85-8F, was found to be operating normally without internal malfunctions, investigators examined the crankshaft (part number A5334).
Laboratory analysis of the crankshaft revealed fatigue fractures. Specifically, the investigation identified surface scratches and indentations within the keyway of the crankshaft. These surface irregularities acted as stress concentrators, which facilitated the material fatigue process. Investigators also noted that the installed Cruzeiro 183-BA-119 propeller was not compatible with the Continental C85-8F engine according to the operational specifications (EA-6501-02) issued by the Aerospace Technical Center (CTA).
Findings
- Material fatigue of the crankshaft at the keyway was the primary cause of the propeller separation.
- Surface scratches and deformations in the keyway acted as stress concenters, accelerating the fatigue mechanism.
- It is hypothesized that the damage to the crankshaft likely occurred during maintenance procedures, specifically during the removal or installation of the propeller.
- The installed propeller model was incompatible with the engine type according to established technical specifications.
- Maintenance practices regarding the handling of crankshafts and component compatibility were identified as contributing factors.