What happened
On October 29, 2024, an Air Tractor AT-301, registration HK5177, was conducting agricultural spraying operations over banana plantations in the Zona Bananera municipality, Magdalena, Colombia. The aircraft departed from La Lucha airfield (9DL) for a scheduled mission involving the spraying of several plots.
Shortly after takeoff, the pilot reported hearing an unusual noise coming from the engine. Although cockpit parameters initially appeared normal, the aircraft began to lose altitude and failed to maintain an adequate climb rate. The pilot declared a Mayday via internal frequency and performed a forced landing in an unprepared field at Finca Burdeos. Upon impact, a post-crash fire erupted, destroying approximately 80% of the aircraft's structure and affecting nearby crops. The pilot sustained minor burns but successfully evacuated the wreckage.
The investigation
The GRIAA investigation focused on the mechanical condition of the Pratt & Whitney R-1340-AN1 engine and the aircraft's maintenance history. Investigators examined the wreckage, noting that the impact caused the aircraft to pivot to the right due to the interaction of the engine and right main gear with the terrain. The investigation also confirmed that the fire occurred after the landing rather than during flight.
A detailed teardown of the engine at an authorized workshop revealed that the supercharger section had suffered significant internal damage. Specifically, investigators found wear on the impeller faces and material loss on the impeller shaft teeth. While the engine's overall components were within certain manufacturer limits, the investigation highlighted a lack of statistical traceability regarding the engine's total time in service (TSN), which complicated the verification of component life limits.
Findings
- The primary cause of the accident was a gradual failure of the impeller shaft bearing.
- This bearing failure induced eccentricity and misalignment, causing the impeller to rub against the supercharger casing.
- The resulting mechanical friction led to reduced air compression within the superdrag/supercharger system.
- This loss of compression decreased the air-fuel mixture delivered to the cylinders, resulting in a significant loss of engine power during the critical climb phase following takeoff.
- The aircraft's weight reduced the available margin for maneuvering once power was lost.