What happened
On December 9, 2023, at approximately 06:30 local time, an Air Tractor AT-301, registration HK4952, was conducting agricultural spraying operations over banana crops in the Zona Bananera municipality, Magdalena. The flight originated from La Lucha airfield (9LD) for work near the Marte farm.
During the third spray pass, the pilot noticed the smell of burning oil. Shortly thereafter, the engine's oil pressure dropped, the chip detector light illuminated, and engine temperatures began to rise. The pilot observed oil leaking from the right side of the aircraft accompanied by heavy engine vibrations. While attempting to divert to the Orihueca airfield (ORH) for an emergency landing, the pilot determined that the aircraft could not reach the runway and instead executed a forced landing in a nearby banana plantation at the Finca La Sierra.
The aircraft sustained substantial damage, including significant impact to the wing leading edges, damage to the ventral section near the spray pump, and the separation of the left main landing gear. The pilot evacuated the aircraft without injury, and no post-impact fire occurred.
The investigation
The GRIAA investigation focused on the mechanical failure of the Pratt & Whitney R-1-340 radial engine. Investigators examined the engine's internal components and maintenance records. The probe revealed that metal shavings were present in the engine crankcase. Physical examination of the cylinders showed discoloration due to extreme heat and plastic deformation at the connection points of the connecting rod bolts to the master rod.
Maintenance record reviews indicated that while the aircraft was airworthy and compliant with maintenance programs, there were discrepancies in documentation. Specifically, certain items in the flight log were not completed, and the operator had failed to account for the Time Since Overhaul (TSO) hours provided by the repair shop. Additionally, the investigation noted that the engine had previously undergone bench testing due to low oil pressure earlier in the year, but the traceability of its removal was not clearly documented.
Findings
- The primary cause of the accident was the obstruction of the lubrication lines between the crankshaft and the master connecting rod.
- This obstruction caused excessive friction and high temperatures, leading to engine seizure and the separation of all connecting rod bolts.
- A gradual oil leak occurred during flight, likely due to the poor condition of the lubrication lines for the cylinder valves.
- The pilot's decision to execute a forced landing in an unprepared field was a direct result of the engine failure during flight.