Incident Overview
On March 23, 2018, a Cessna 182C, registration LV-GMG, departed from Aeroclub San Rafael at 11:50 UTC for an aerial application flight. The aircraft, loaded with full fuel, conducted sterile insect dispersal over a predetermined area at a cruising altitude of 1,500 feet above ground. During cruise, the engine and propeller stopped. The pilot executed an emergency landing in an unprepared field at minimum speed (55 knots) with full flaps. The touchdown was smooth and controlled, but due to soft ground, the nose wheel sank and collapsed. The aircraft nosed over and came to rest facing 180 degrees. The accident occurred in daylight and good weather conditions. The two occupants, the pilot and one companion, were uninjured. The aircraft sustained substantial damage.
Investigation Findings
The engine failure was caused by a severe internal failure. Examination of the Continental IO-470-R engine at Aerotec S.A. revealed that the connecting rod of cylinder number 4 had detached from the crankshaft. The rod struck the upper part of the engine block, creating a 12 cm hole. Investigators checked all connecting rod nuts for torque and compared them to the manufacturer's specification (690-710 in/lb per Service Bulletin SB96-7C). The nut on the number 4 connecting rod was found completely unscrewed. This allowed the rod cap to separate, deforming and fracturing the remaining bolt, leading to the rod's complete detachment. All other connecting rod nuts showed torque values below the required range.
The aircraft's landing marks indicated a smooth three-point touchdown, with a 57-meter ground roll before encountering a small elevation change. That impact caused the nose gear to collapse and the aircraft to nose over. The propeller blades showed pronounced plastic deformation without leading-edge damage, consistent with the engine being stopped at impact. The lubrication system functioned until the failure, with no signs of abnormal wear or high temperatures on bearings.
Conclusion and Probable Cause
The investigation concluded that the engine failure was the immediate triggering event. The connecting rod detached because the nut on the rod-to-cap bolt loosened due to insufficient torque during assembly. This allowed bolt deformation and fracture. The probable cause of the accident was the incorrect torque applied to the connecting rod nut, leading to its loosening, connecting rod failure, and engine stoppage.