What happened
On February 11, 2021, a Thrush S2R-T34, registration F-HLDD, was conducting a locust spraying mission in the Arsi Zone of Ethiopia under the support of the FAO. After successfully completing an initial mission, the pilot departed Robe Airport at 05:57 UTC for a second target located 45NM away.
During the flight, the aircraft crossed a mountain ridge and began a descent following the terrain. As the aircraft moved through a valley, it encountered rising terrain. The pilot maintained a low altitude of approximately 200 feet above the ground, likely due to cloud cover restricting higher flight. As the aircraft climbed along a gradual, nearly imperceptible upward slope, the ground speed steadily decreased.
Shortly before reaching the target, the pilot performed maneuvers to navigate the terrain. At approximately 0 6:20 UTC, the aircraft's tracking signal was lost. The aircraft subsequently performed a forced landing on a plateau. Upon touchdown, the landing gear struck a mound, causing the aircraft to hit a second mound head-on. The impact caused the aircraft to rotate 150 degrees and catch fire. The pilot was evacuated by local residents but succumbed to injuries sustained in the fire two days later.
The investigation
The investigation examined the aircraft's flight path using Spidertracks data, analyzed meteorological reports from Meteo France, and reviewed maintenance and mission records. Investigators reconstructed the trajectory, noting that the aircraft was climbing at a rate of approximately 430 feet per minute while the ground speed dropped below 95 knots. The investigation also reviewed the pilot's experience, noting he was a highly qualified agricultural sprayer with over 7,000 total flight hours. Witnesses at the site reported seeing white smoke, suggesting the pilot may have been dumping chemical products prior to the impact.
Findings
- The pilot was an experienced agricultural specialist with a valid medical certificate.
- The aircraft and engine were well-maintained according to standard procedures.
- The pilot failed to perceive a gradual increase in terrain elevation due to a lack of external visual references.
- Weather analysis indicated a cloud layer was present, which likely forced the pilot to fly at a very low altitude to maintain visual contact with the ground.
- The terrain featured a "false flat" rising slope of approximately 2.6%, which contributed to the unnoticed loss of airspeed.
- The landing site was characterized by difficult-to-identify mounds and ditches that were not easily visible from the air.