What happened
On September 25, 2012, a Bell 206B helicopter, registration PT-HSN, was attempting to take off from Helisul IV Heliport in Foz do Iguaçu, Brazil, for a scenic flight. As the pilot applied power to initiate the takeoff, the aircraft suddenly experienced a high rate of descent and struck the concrete helipad surface at an altitude of approximately three meters. The impact resulted in substantial damage to the aircraft. The pilot and two passengers sustained serious injuries, while one passenger suffered minor injuries.
The investigation
CENIPA investigators examined video footage of the impact, which revealed that the pitch control rods of the main rotor were twisting toward the mast just before the collision. This mechanical movement caused the blade pitch to drop to a negative value, effectively pushing the aircraft toward the ground despite the engine producing normal takeoff power.
Technical analysis of the rotor head identified a fracture in the trunnion, the component responsible for coupling the main rotor head to the mast. The investigation found that fatigue had initiated on the external surface of the trunnion due to surface scratches that acted as stress concentrators. These scratches were only visible after removing the component's paint and sealant. Furthermore, the investigation revealed that the trunnion had exceeded its required overhaul interval by 1,085 hours due to an error in the operator's maintenance hour tracking.
Findings
- Component Fatigue: The trunnion fractured due to fatigue initiated by surface irregularities.
- Maintenance Overdue: The trunnion had accumulated approximately 5,885 total hours, significantly exceeding the 4,800-hour overhaul limit.
- Management Oversight: A failure in managerial supervision allowed an error in the maintenance tracking logs to go undetected, resulting in the use of a critical component past its service life.
Safety action
CENIPA issued recommendations to the National Civil Aviation Agency (ANAC) to evaluate the accuracy of the operator's maintenance records and to review the effectiveness of the company's Emergency Response Plan, specifically regarding medical support and fire response capabilities.