What happened
On June 24, 1997, an S-61N Sea King, registration PT-YAF, operated by Aeróleo Táxi Aéreo, was performing a maintenance test flight at Macaé Airport (SBME) in Rio de Janeiro. The flight was intended to verify the integrity of recent maintenance work, which included the replacement of an engine, a tail rotor, and a left primary servo.
Prior to takeoff, the pilot identified an anomaly in the flight controls: the right-side cyclic control was returning to its original position due to a spring effect, whereas the left side remained static. After confirming this abnormal behavior on a different aircraft, the crew—which included the pilots, mechanics, and a manufacturer representative—decided to proceed with the flight, performing a hover at low altitude to test the hydraulic systems.
During the testing of the primary hydraulic system, the crew deactivated the auxiliary system. This action triggered a sudden lateral movement to the left, followed by a right-side tilt and an uncontrolled rotation around the vertical axis. Despite attempts to use the cyclic, pedals, and power reduction, the crew could not regain control. The helicopter struck the ground, impacting the main rotor blades first, followed by the right side of the fuselage, resulting in severe damage to the rotor, tail boom, and engines. The two pilots sustained minor injuries, while the other three occupants were uninjured.
The investigation
CENIPA's investigation focused on the maintenance procedures and the flight crew's decision-making. Technical examinations of the hydraulic components, conducted in coordination with engineers in the United States, revealed that the primary left servo had been installed without the necessary "sloppy link" bushings.
Investigators found that during the replacement of the servo, an auxiliary mechanic had removed the old bushings but failed to reinstall them on the new unit. This omission caused the hydraulic servo to operate improperly, characterized by abnormal forces and the potential for the piston to jam. The investigation also highlighted a breakdown in crew coordination and maintenance oversight, noting that the maintenance supervisor had failed to properly inspect the work performed by the mechanic.