What happened
On August 14, 2001, a Bell 407 helicopter, registration PT-YZD, operated by the Brazilian Federal Police, was performing a local instructional flight at the Brasília Model Aircraft Track. The flight was intended for pilot adaptation, involving various maneuvers such as simulated hydraulic failure landings and running landings. The crew consisted of an instructor pilot and a student pilot.
During the execution of a running landing following an autorotation exercise, the aircraft's main rotor blades collided with the left vertical finlet of the horizontal stabilizer. The collision occurred as the pilot attempted to decelerate the aircraft at the end of the runway. The impact caused damage to the upper portion of the vertical finlet, compromising the aircraft's airworthiness.
The investigation
CENIPA investigators determined that the collision occurred due to intense control inputs applied as the aircraft reached the end of the limited runway. To stop the forward movement, the pilot applied significant aft cyclic and low collective commands. This maneuver caused the rotor disk to tilt and the blades to flex downward, reducing the clearance between the blade tips and the stabilizer.
The investigation found that the aircraft's hydraulic system was engaged, making the cyclic controls highly sensitive. Additionally, the aerodynamic effect of the advancing blade on the right side caused the left side of the rotor disk to dip. The investigation also noted that the aircraft's flight manual advises pilots to disregard the cyclic position warning light during running landings on uneven terrain, even though the light is designed to prevent large control amplitudes on the ground.
Operational deficiencies were also identified. The training area—a narrow, 10-meter wide model aircraft track—lacked necessary emergency infrastructure and provided an extremely slim margin for error. Furthermore, the operator's training program was found to be outdated, as the listed missions did not correspond to the specific equipment being flown.
Findings
- Design Deficiency: The structural clearance between the rotor blades and the vertical fin was insufficient to prevent contact during the specific control inputs described.
- Deficient Supervision: The Federal Police training department permitted instructional maneuvers in an inadequate location with insufficient runway width.
Deficient Judgment: The instructor selected a training site that lacked the necessary dimensions and safety infrastructure for the maneuvers being performed.
- Operational Risk: The use of aggressive aft cyclic inputs during running landings on this aircraft type poses a significant risk of rotor-to-stabilizer contact.