What happened
On 12 May 2007, a Piper Pawnee PA 25-2Spl aircraft, registration PK-PNM, was performing routine agricultural spraying operations for PT Perkebunan Nusantara II at the Klumpang tobacco plantation in Deli Serdang, North Sumatra. During its third flight of the day, the aircraft was maneuvering between spray lines in areas 5 and 6.
After completing a pass on the first line, the pilot climbed to 200 feet and initiated a right turn toward the next target. As the aircraft descended to approximately 150 feet while crossing a river, the pilot experienced a sudden loss of power and altitude. In an attempt to recover, the pilot applied full throttle; however, the aircraft encountered a downdraft that caused the right wing to strike a cluster of bamboo trees. The impact caused the aircraft to lose control and crash into the vegetation. The pilot sustained minor injuries, while the aircraft suffered major damage.
The investigation
The investigation examined the aircraft's flight path, the environmental conditions, and the impact site. Investigators noted that while the plantation terrain is generally flat, the presence of irrigation rivers and taller vegetation, such as bamboo, oil palm, and teak, creates a complex flight environment.
Witnesses at the scene, including an aircraft maintenance engineer, reported extremely strong and sporadic winds coming from approximately 300 degrees. This contradicted the official meteorological report, which indicated a wind of 120 degrees at 8 knots. The investigation also looked at the aircraft's load, noting it was carrying 100 liters of pesticide and 100 liters of fuel, operating within approved weight and balance limits.
Findings
- The aircraft was airworthy and the pilot held a valid commercial license.
- The aircraft was operating at a high load weight during low-altitude maneuvers.
- The primary cause of the accident was the aircraft encountering turbulence and a downdraft at a low altitude, which led to an uncontrolled impact with bamboo trees.