What happened
On December 8, 2001, an AT-401B agricultural aircraft, registration PT-XCA, was performing crop dusting operations over a soybean field near Alto Garças, Mato Grosso. While the pilot was executing a left-hand turn to return to the application area, a sudden jolt was felt in the control column. The pilot immediately realized that the aileron controls were no longer responsive.
In an attempt to regain control and reduce the aircraft's weight, the pilot jettisoned approximately 1,400 liters of agricultural chemicals. Despite this emergency action, the aircraft continued its leftward bank until the left wingtip struck the ground. The impact caused extensive damage to the propeller, stabilizers, wing, and left aileron, and the engine was torn from the airframe. The pilot sustained minor injuries.
The investigation
CENIPA investigators examined the wreckage and the aircraft's maintenance history. The aircraft was relatively new, having flown only 105 hours since its manufacture in 2000, and its maintenance records were up to date. The investigation focused on the sudden loss of lateral control during the maneuver.
Investigators recovered a broken bolt that had been used to secure the left aileron assembly. Upon inspection, it was determined that this bolt did not meet the manufacturer's specifications; it was smaller in diameter than the required part (PN AN3-13) and had been sourced from a different area of the aircraft's structure. The bolt showed clear evidence of fatigue and friction marks, indicating it had failed due to excessive stress.
Findings
- The primary cause of the accident was the failure of an improperly sized bolt used in the left aileron assembly.
- The use of a bolt with a smaller diameter than specified prevented the component from withstanding the aerodynamic loads encountered during the turn.
- The investigation could not definitively determine if the incorrect part was installed during the initial manufacturing process or during subsequent maintenance, though the aircraft's low flight hours suggested it likely contained original factory components.
- Meteorological conditions were favorable for visual flight operations at the time of the occurrence.