What happened
On October 27, 2020, a commercial pilot was conducting aerial spraying operations over the Fundo La Rosa in the Las Cabras commune, Chile. Approximately 10 minutes into the flight, while performing the fourth spraying pass at an altitude of only 25 meters and a speed of 80 mph, the engine of the Grumman G-164A suddenly ceased operation.
With very little time to react due to the low altitude, the pilot was forced to perform an emergency landing in an unprepared area near the flight path. The aircraft struck the terrain at a nose-down angle, causing it to bounce and subsequently flip onto its back. The pilot was able to exit the aircraft safely and sustained no injuries, though the aircraft suffered significant damage.
The investigation
DGAC Chile investigators examined the aircraft, the engine, and the maintenance records. The investigation focused on the mechanical state of the Pratt & Whitney R985AN-14B engine and the circumstances of the impact.
Investigators found that the aircraft had undergone a 100-hour inspection just 11.3 hours prior to the accident, and no discrepancies regarding the engine or supercharger were noted at that time. Fuel analysis confirmed that the AVGAS 100LL used was within standard parameters and that sufficient fuel was on board for the mission. The inspection of the wreckage revealed that the propeller blades showed no signs of rotational energy at impact, confirming the engine had stopped before contact with the ground. The damage to the airframe, including the detached landing gear and deformed wings, was consistent with the impact and subsequent inversion.
Findings
- The primary cause of the accident was an engine failure in flight caused by the degradation of the bearings supporting the impeller shaft within the supercharger system.
- This bearing degradation caused the impeller shaft to become off-center, leading to wear on the supercharger case and a loss of lubrication for the gear train.
- The failure caused a loss of compression in the air-fuel mixture entering the engine cylinders and resulted in broken gear teeth where the system connects to the engine's crankshaft.
- The low altitude of 25 meters and the low airspeed at the time of the failure left the pilot with insufficient time to execute a controlled landing, necessitating the emergency maneuver in unprepared terrain.