What happened
On June 12, 2012, at approximately 11:10 a.m., a Cessna 150M, registration HI 561, performing a flight instruction mission, was forced to perform an emergency landing in a field near Monte Adentro, Licey al Medio, Santiago. The aircraft had departed from Cibao International Airport. While flying approximately two miles northwest of the station, the crew experienced a loud noise from the engine followed by a complete engine shutdown and a total loss of electrical power.
The instructor pilot took control and selected a nearby agricultural field for the emergency landing. Due to the uneven, furrowed terrain of the field, the aircraft struck the ground and subsequently overturned, landing in an inverted position. Both occupants of the aircraft, the pilot and the student, escaped the wreckage without injury.
The investigation
The CIAA investigation focused on determining why the engine failed and why the electrical system lost power. Investigators examined the engine, the flight controls, and the propeller. A metallurgical analysis of the propeller was conducted by the manufacturer, Cessna Textron Company, to examine the fracture of one of the propeller blades.
Physical examination of the engine revealed that the intense vibrations caused by the propeller failure led to the detachment of the starter motor and the right magneto, which resulted in the loss of engine timing and subsequent shutdown. The vibrations were also severe enough to disconnect the battery, leaving the crew without communication capabilities. The investigation also confirmed that the aircraft's maintenance was up to date, with the last 100-hour inspection completed in May 2012.
Findings
- The primary cause of the accident was a propeller blade failure resulting from high-cycle fatigue.
- Metallurgical analysis showed that the fatigue cracks originated from areas of corrosion damage on the leading edge of the blade.
- The corrosion damage included pitting and intergranular cracking, which served as the initiation point for the fatigue fracture.
- The resulting aerodynamic imbalance created extreme vibrations that physically displaced engine components (starter and magneto) and disconnected the electrical system.