What happened
On July 13, 1996, a Piper PA-36-285 aircraft with registration CS-AUB, owned by Avitrata, departed from the Benavente airfield at approximately 14:00 H for agricultural aerial work in the Vale de Cavalos area. The pilot, a 43-year-old commercial pilot with over 4,100 hours of total experience and recent currency on this aircraft type, was conducting crop dusting operations.
At approximately 15:10 H, the aircraft attempted to land on an improvised dirt track in Vale de Cavalos. This strip was normally used as an agricultural access road, characterized by a good pavement surface but extremely narrow width and no safety margins. Moderate rainfall had occurred earlier in the day, leaving the ground slippery. Upon touchdown, the main landing gear contacted the runway, but the aircraft immediately veered to the right. Despite the pilot's attempts to correct the trajectory, the limited width of the strip prevented recovery. The aircraft exited the paved surface, entering a vineyard on the right side. During this excursion, the left main landing gear strut fractured, and the left wing struck the ground, sustaining substantial damage. The aircraft came to a stop after rotating approximately 90 degrees. There were no fatalities or injuries; the cockpit remained intact, and the seat belts withstood the impact forces.
The investigation
The GPIAAF (Gabinete de Prevenção e Investigação de Acidentes com Aeronaves) investigated the circumstances and causes of the accident. The examination confirmed that both the pilot and the aircraft were properly certified and airworthy prior to the flight. The operator, Avitrata, held a valid license for aerial work from the DGAC.
The investigation focused on the landing site conditions, the aircraft's mechanical status, and the pilot's actions. The runway was identified as a dirt track with insufficient width and no lateral safety strips. The wet condition of the surface, resulting from earlier rain, contributed to reduced traction. An examination of the wreckage revealed that the left main landing gear leg broke during the excursion, leading to the left wing impacting the ground. The brake system showed no signs of malfunction prior to the incident. However, a discrepancy was noted in the altimeter installation: it was set in inches of mercury rather than meeting the technical approval requirements for altimetric setting defined in CS 23.1323.
The operator's Flight Operations Manual was found to be deficient regarding the notification of accidents and incidents, as they were unaware of specific DGAC regulations on this matter. The pilot had sufficient recent experience with the aircraft type, having flown 124 hours in the last 90 days.
Findings
The probable cause of the accident was determined to be an improper execution of the landing maneuver by the pilot. Contributing factors included the wet condition of the runway surface and the absence of lateral safety strips on the narrow improvised airstrip. The aircraft's braking system and flight controls functioned normally up to the point of impact. The operator's lack of awareness regarding accident reporting regulations was also noted as a procedural deficiency.
Safety action
The GPIAAF issued safety recommendations urging operators to utilize airfields that meet minimum safety requirements whenever possible. Additionally, it recommended that Avitrata revise its Flight Operations Manual to include specific procedures for the notification of accidents and incidents.