What happened
On July 29, 2002, at approximately 19:00 local time, an Air Tractor AT-802, registration EC-GHL, was conducting aerial forest fire surveillance operations in the province of Barcelona. The aircraft, operated for firefighting purposes, had been active throughout the day, performing water drops near Nova de Segre and visiting various aerodromes including Igualada and La Seu d’Urgell.
While flying near Cardona, the aircraft experienced an engine failure in flight. The pilot attempted to restart the engine but was unsuccessful, necessitating an emergency landing. The pilot identified a harvested cereal field and attempted to land within it. During the approach, the aircraft clipped the treetops of adjacent pines. The subsequent heavy impact caused the aircraft to bounce across the field, resulting in the breakage of the tail skid and a loss of control. The aircraft eventually came to a stop after the right wing struck a tree. The aircraft sustained serious damage to both wings, the tail skid, the depth rudder, the propeller, and the main landing gear. The pilot escaped the accident without injury.
The investigation
The investigation focused on the cause of the engine failure and the condition of the fuel system. The aircraft's engine, a Pratt & Whitney PT6A-67AG, was inspected by the manufacturer. While damage was found on the compressor turbine blades and the power turbine, these findings were not considered significant enough to have caused the engine failure, though they may have reduced performance.
Inspectors examined the fuel system, which consists of two wing tanks feeding a central header tank. Upon draining the tanks, it was discovered that the right tank was completely empty, while the left tank contained approximately 200 liters. This imbalance occurred because the fuel system allows free flow between tanks, and the left tank was positioned lower than the right, causing fuel to migrate via gravity.
Findings
- The engine failure was likely caused by fuel starvation resulting from a significant imbalance between the two wing tanks.
- The fuel system design allowed fuel to migrate from the right tank to the left tank, eventually emptying the right tank and the central header tank.
- The aircraft had not been equipped with any of the manufacturer's recommended modifications to improve fuel indication or prevent migration, such as a dual fuel gauge or a larger header tank.
- The engine's internal damage was not the primary cause of the shutdown, as no foreign object damage (FOD) was found in the forward sections of the engine.