What happened
On December 22, 2007, a Piper PA-25-235, registration PT-DNR, was performing an agricultural spraying mission over a banana plantation in Schroeder, Santa Catarina, when the pilot experienced a sudden, loud noise followed by intense vibrations. The pilot, unable to maintain stable control of the aircraft, initiated emergency procedures and directed the plane toward an uninhabited area.
The pilot attempted a forced landing in a clearing located between a river and the plantation. During the approach, the left wing and left landing gear struck banana trees before the aircraft collided with the ground. The impact caused the left landing gear to be torn from the airframe and resulted in substantial damage to the propeller, left wing, aileron, and flaps. The pilot emerged from the accident uninjured.
The investigation
CENIPA investigators determined that the intense vibrations and subsequent difficulty in controlling the aircraft were caused by the loss of a portion of one of the propeller blades. The aircraft was equipped with a McCauley 1A200/FA8452 propeller.
Technical analysis revealed that a fracture had occurred at the final section of the propeller blade. The investigation established that the root cause was a fatigue process that originated from an impact mark on the lower surface of the blade. This impact mark acted as a stress concentrator, facilitating the propagation of a fatigue crack.
Records showed that the propeller had undergone a 100-hour inspection in November 2007, and the aircraft's annual maintenance was valid. However, the investigation noted that the maintenance program for this specific propeller did not include non-destructive testing (NDT) to detect internal discontinuities or cracks following its last overhaul in 2005. While the maintenance performed by authorized workshops was adequate and up to date, the fatigue process went undetected.