What happened
On November 19, 2016, an AS 350 B3 helicopter, registration PR-IDR, operated by the Rio de Janeiro State Military Police (PMERJ), crashed in the Jacarepaguá region of Rio de Janeiro. The aircraft was conducting a local surveillance mission in support of police operations.
While the crew was performing a hover at an altitude of approximately 1,000 feet, the aircraft experienced an uncommanded leftward yaw. This led to a loss of directional control, causing the helicopter to spin around its vertical axis. As the aircraft lost altitude, it struck the ground on the banks of a river with high vertical speed and a steep impact angle. The crash resulted in four fatalities, as all crew members on board perished due to the impact forces. The aircraft sustained substantial damage.
The investigation
CENIPA's investigation focused on the aerodynamic phenomena occurring during the hover. Testing conducted during the investigation revealed that in the event of a tail rotor drive failure while hovering outside of ground effect, the aircraft would enter an undamped left yaw. This rotation rate was observed to increase significantly—from 33°/s to 57°/s—upon the application of the collective control, nearly reaching the aircraft's structural limit of 60°/s.
Investigators examined the flight profiles and the crew's reactions. The investigation established that the aircraft was considerably heavy at the time of the accident and was operating at a height and speed that left little margin for error. The wreckage analysis showed that the main rotor blades suffered significant damage consistent with impact while rotating, and the tail boom had disconnected due to the shearing forces of the crash.
Findings
- Loss of Tail Rotor Effectiveness (LTE): The primary aerodynamic trigger was an uncommanded yaw that the crew could not counteract.
- Inappropriate Control Inputs: The pilots likely applied upward collective control, which increased the yaw rate, and delayed the necessary forward cyclic input to increase translational speed.
- Lack of Specific Training: The crew lacked specialized training in managing aerodynamic phenomena like LTE or unanticipated yaw, which prevented them from executing the correct recovery maneuvers.
- Operational Risks: The mission was conducted at 1,000 feet outside of ground effect while the aircraft was heavily loaded, a condition that reduced the possibility of recovery.
- Organizational Deficiencies: There was an absence of established operational standards or manuals for conducting surveillance hovers in support of police operations, alongside inadequate management oversight regarding mission planning.