History of the Flight
On June 18, 2015, a team providing aerial spraying services arrived at the Biscainho Brandão agricultural airstrip near the farm of the service contractor. The aircraft, a Piper PA36-375 with registration CS-AUC, was prepared for the mission and supplied with fuel and spraying product.
The pilot, while waiting for the ground team to finalize procedures, observed vegetation movement due to wind, indicating a tendency to use runway 13 for take-off. According to the pilot, the wind intensity did not seem to prevent a take-off on runway 31, which had the threshold closest to the filling position.
After aligning on runway 31, the aircraft started the take-off run, which the pilot considered normal and following usual procedures. With flaps set to the first notch, the aircraft did not reach the required airspeed for take-off (80 mph); however, the pilot continued the take-off run.
Ground personnel stated that the aircraft took off at the end of the runway, probably after the initial 450 meters, and oscillatory wing movements were observed. During the final phase of the take-off run, the pilot stated that he selected full flaps without triggering the emergency cargo release system, allegedly because it was inoperative, and this did not avoid loss of control.
The aircraft, unable to overcome obstacles and sinking, initially struck a cork tree with a pronounced left semi-wing down attitude, followed by a collision with a second tree while practically inverted, and finally stopped at the base of a third tree.
The morning had clear skies; wind recorded at a nearby surface station was from the northeast at 5 to 10 knots, temperature 28°C.
It was not possible to measure the aircraft's mass at the time of the accident; fuel and chemical quantities were estimated by the ground crew at 80 and 450 liters, respectively.
Injuries and Damage
The pilot, found unconscious, was removed from the wreckage by a member of the agricultural support team. Multiple rescue teams attended the site; the pilot was evacuated by helicopter to a hospital in Lisbon, where serious chest injuries, head trauma, and various abrasions were confirmed. The aircraft was destroyed. All flight control surfaces were identified and confirmed connected; no evidence of in-flight structural failure was found. The propeller blades appeared in a fine pitch range at impact, consistent with high engine power. Both engine and propeller detached from the primary structure due to forces from the collision with the third tree.
The Agricultural Airstrip
The airstrip, in use for several years, was well known to the operator and injured pilot. It did not comply with (nor was required to have) windsock installation or firefighting and rescue requirements from Regulation No 401/2017, nor conditions from D-L No. 238/2004 and No. 283/2007 for ultralight aircraft runway operations. The declared runway length was 500 meters, with a clearway of about 600 meters and a clay surface. Runway 31 had a positive slope of about +1.7% in the first 400 meters, and at the end of 600 meters there were large cork trees approximately 10 meters high.
Probable Cause
The low speed of aerodynamic control caused a collision with a pronounced left semi-wing down attitude, evidence of aircraft loss of control due to asymmetric aerodynamic stall.