What happened
On January 31, 2004, a Bell 206L-4 helicopter, registration PT-YEF, operated by Helisul Táxi Aéreo Ltda., was performing support operations for a seismic survey in the Amazon rainforest. After landing at a clearing to disembark passengers, the pilot attempted a vertical takeoff. At an altitude of approximately 30 meters, the aircraft's tailboom separated from the main fuselage. This structural failure caused the helicopter to lose all flight control, resulting in a rapid descent characterized by vertical rotation. The aircraft struck trees and the ground, causing extensive damage to the airframe. The pilot, who was the sole occupant, sustained fatal injuries.
The investigation
CENIPA investigators, with assistance from Canada's Transportation Safety Board (TSB), examined the wreckage and the aircraft's maintenance history. The investigation focused on the separation of the tailboom and the condition of the attachment fittings. Laboratory analysis of the fittings revealed that the upper fittings had fractured due to overload, while the lower left fitting showed evidence of fatigue-induced cracking originating near the rivet holes. Scanning Electron Microscopy (SEM) confirmed the presence of fatigue striations and multiple crack initiation sites.
Investigators also reviewed the maintenance records, noting that a 100-hour inspection had been performed just 19 days prior to the accident at a remote base in Porto Passarinho. Unlike the company's main headquarters, this location lacked a hangar or adequate shelter, which may have hindered the ability to detect pre-existing cracks during the visual inspection.
Findings
- The primary cause of the tailboom separation was the failure of the attachment fittings due to fatigue and subsequent overload.
- Inadequate maintenance supervision allowed a 100-hour inspection to be conducted in an environment that did not meet the required standards for proper inspection conditions.
- The lack of a hangar or protective shelter at the remote operating base likely compromised the effectiveness of the visual inspection, potentially allowing pre-existing fatigue cracks to go undetected.
- Evidence of corrosion was found on the attachment fittings, which may have contributed to the initiation of the cracks.