What happened
On May 9, 2002, at approximately 12:00 PM, a PA-25-235 agricultural aircraft, registration PT-WKB, was performing crop dusting operations over a banana plantation in Luiz Alves, Santa Catarina. During the fifth and final pass of the day, the pilot was flying at a low altitude in a perpendicular direction to the area when the right wing suddenly detached from the fuselage. The loss of structural integrity caused the pilot to lose control, resulting in a collision with the ground. The aircraft was destroyed upon impact. The pilot was recovered from the wreckage unconscious but sustained only minor injuries.
The investigation
CENIPA investigators examined the wreckage and conducted metallurgical analysis through the Aerospace Technical Center (IFI/CTA). Laboratory tests on components of the right wing attachment points and spars revealed that a fracture had initiated from a subcritical crack at a threaded hole on the surface. Scanning electron microscopy confirmed that the crack propagated via an intergranular mechanism. Further metallographic examinations identified other subcritical cracks associated with corrosion.
The investigation also reviewed maintenance records, which revealed that the aircraft's airworthiness logs for the airframe, engine, and propeller were outdated. Several scheduled inspections, including two 50-hour inspections and one 100-hour inspection, were missing from the records. Additionally, the investigation found that several mandatory Airworthiness Directives (ADs) related to wing strut corrosion and wing attachment prevention had expired in May 2002.
Findings
- The primary cause of the accident was the separation of the right wing due to structural failure caused by stress corrosion cracking.
- Maintenance deficiencies prevented the detection of corrosion and cracks in the wing spars.
- There was a lack of oversight regarding the aircraft's scheduled inspections, as evidenced by the missing 50-hour and 100-hour inspection records.
- Several mandatory Airworthiness Directives (AD 93-10-06, AD 95-12-01, and AD 99-01-05) intended to prevent in-flight wing separation had expired.
- Maintenance was being performed by a workshop that was not officially certified for this specific aircraft type.
- The operator failed to properly supervise the maintenance program and the continuity of required inspections.