What happened
On April 11, 2003, a Piper PA-25-260 Pawnee was conducting a solo agricultural flight training mission at the Sebastián Almagro Aerodrome in Palma del Río, Córdoba. The pilot was performing maneuvers to obtain an agricultural pilot rating, with an instructor monitoring the progress from the ground.
During the second training period of the day, the pilot took off from runway 25 with an estimated water load of 300 to 400 liters. At an altitude of approximately 100 feet, the pilot reduced engine power to level the aircraft and prepare for a left turn to execute a standard water drop. During this phase, the pilot noticed abnormal engine behavior and attempted to apply full power; however, the aircraft's performance did not improve.
In an attempt to manage the situation, the pilot initiated the water drop while maintaining the runway heading. The sudden release of the water load caused a severe pitch-up moment. The aircraft reached an extreme angle of attack, leading to a stall and a left wing drop. The aircraft subsequently plummeted, impacting an olive grove with a nose-low attitude and left bank. The impact destroyed the aircraft.
The investigation
The CIAIAC investigation focused on the sequence of events leading to the loss of control and the failure of the pilot's restraint system. Investigators examined the engine performance, noting that the mixture lever had likely been inadvertently retarded from the rich position, causing the perceived engine malfunction.
Crucially, the investigation scrutinized the shoulder harness system. Although the pilot suffered head injuries from striking the instrument panel, the investigation revealed that the harness failed to properly restrain the pilot during the impact. The investigation found that the retractor mechanism was not functioning as an inertial reel, contrary to common pilot belief. Furthermore, the locking mechanism was inoperative due to a misadjusted stop, and the internal cable had detached from its hollow screw connection, allowing the harness to extend freely until it reached its limit.
Findings
- The primary cause of the accident was the excessive pitch-up moment caused by the sudden release of the water load, which led to an unrecoverable stall at a low altitude.
- The pilot's perception of engine failure, likely caused by an inadvertent reduction in fuel mixture, contributed to the decision-making process during the maneuver.
- The aircraft's restraint system was defective: the retractor lacked inertial capabilities, the locking mechanism was misadjusted, and the cable-to-screw connection had failed.
- The pilot's injuries were exacerbated by the failure of the shoulder harness to maintain proper tension during the impact.