What happened
On August 4, 2004, an AS-350 B2 helicopter, registration PR-HFB, operated by the Federal Police, was conducting a visual flight rules (VFR) mission from Ponta Porâ to a farm near Coronel Sapucaia, Mato Grosso do Sul. As the crew approached the landing site, they executed a steep approach to avoid obstacles such as a corral and low vegetation.
At an altitude of approximately 15 meters, the aircraft experienced a sudden left yaw and began an uncontrolled rotation. The pilot attempted to correct the descent by increasing main rotor torque; however, this action increased the yaw rate. The tail rotor struck the ground, causing the aircraft to capsize and the main rotor to impact the terrain. The accident resulted in one fatality (the tactical operator), two serious injuries (the pilots), and three minor injuries (the passengers). The aircraft was destroyed.
The investigation
CENIPA investigators examined the wreckage and the flight control components, including the tail rotor control rod and teleflex cable. Microscopic analysis conducted by the Technical Center of Aeronautics (CTA) confirmed that the fractures in these components were the result of structural overload during the impact, rather than mechanical failure during flight. Technical inspections by Helibrás also confirmed that the tail rotor drive system was functioning correctly until the collision.
The investigation also reviewed the operational conditions, noting that the aircraft was operating at a weight of approximately 2,217 kg at the time of impact, which was within limits, though the takeoff weight had slightly exceeded the maximum allowable limit. The investigation also addressed the crew's experience, noting that while the pilot was qualified, the co-pilot was still undergoing training for this specific model.
Findings
- Loss of Tail Rotor Effectiveness (LTE): The combination of high power settings, a steep approach angle, and gusty winds contributed to the loss of directional control.
- Environmental Factors: Strong and variable winds, characterized by gusts, significantly impacted the effectiveness of the tail rotor.
- Pilot Input: The application of increased collective pitch to arrest the descent, combined with improper pedal usage, exacerbated the uncontrolled yaw.
- Operational Judgment: The crew selected a landing site that required a high-power, steep-angle approach under challenging meteorological conditions.