History of the Flight
On Thursday, 10 May 2007, at 12:35 local time, a Piper PA-36 (registration EC-CUU) operated by Trabajos Aéreos Espejo was conducting fumigation work over oak trees near Añora, Córdoba. It was the third flight of the day, with the first two flights lasting approximately 90 and 60 minutes respectively. Fifty-five minutes into the third flight, as the aircraft climbed out of a spraying run, the engine experienced a loss of power. The pilot engaged the electric fuel pump, which restored power momentarily, but the power quickly dropped again. The pilot then disengaged the pump and prepared for an emergency landing.
The landing took place in a wooded area. During the landing run, the aircraft sustained extensive damage to the frame and wings. The main landing gear and tail wheel detached, and the right wing fuel tank ruptured when the right landing gear leg lodged in the ground. The pilot, the sole occupant, exited the aircraft uninjured.
Investigation Findings
Inspections at the accident site revealed the left fuel tank was approximately half full. The right tank had broken off and was empty, with significant fuel spillage on the ground. Examination of the engine components showed the mechanical fuel pump was completely seized and its axle shaft broken. The propeller exhibited signs that the engine was turning with negligible power at impact.
Disassembly of the mechanical fuel pump (P/N RG9080J6A, S/N D-263) revealed the rotor was broken in four places and a crack on the rear cover of the pressure vessel. Two foreign objects, each about 5 mm in size, were found inside: a piece from a manufactured plastic component with a carbon-like appearance, and a metallic piece appearing to be a small section of flattened tube. It was concluded that the metallic object had wedged between the rotor and stator, causing the pump to seize.
Electric Pump and Fuel Filter Inspection
The auxiliary electric pump (P/N 2B6-36, S/N 4AK2) was examined. All four impeller blades were seized in their housing grooves; one blade had broken in half, and all showed abnormal wear near the suction port. The carbon-like object found in the mechanical pump was identified as the missing half of the electric pump's impeller blade. Additionally, the positioning pin from the rear cover of the electric pump's pressure vessel was missing. The metallic debris in the mechanical pump was determined to be from that missing pin.
The fuel filter, located upstream of the electric pump, was found in good condition with no obstructions. No record of similar failures was found during the investigation.
Procedures and Analysis
The operator used the aircraft's Flight Manual procedures. Normal procedure required the electric pump for takeoff, approach, and landing. The emergency procedure for an in-flight loss of power at low altitude called for immediate preparation for an emergency landing and disengagement of the electric pump; at sufficient altitude, engaging the electric pump was advised.
Analysis indicated the positioning pin on the electric pump's rear cover broke loose for unknown reasons. The loose pin caused blade breakage and wear in the electric pump. Both the pin and the broken blade section were swept by fuel into the mechanical pump. The pin wedging between rotor and stator caused the mechanical pump to seize, leading to the engine power loss. The poor condition of the electric pump blades prevented successful power recovery when engaged. The pilot followed the emergency procedure for low altitude, but the correct action per the manual was an immediate emergency landing; however, the wooded terrain made a controlled landing difficult.