What happened
On September 13, 2020, an AS 350 B3 helicopter, registration PP-MRA, operated by the State Secretariat for Public Security, was performing a routine aerial patrol flight near Arapiraca Aerodrome (SNAL) in Alagoas, Brazil. The flight, which included two pilots and three police officers, was returning to the aerodrome after a local mission.
During the air taxiing phase, while performing a 9/0-degree left turn to enter a taxiway leading to the apron, the aircraft experienced a sudden loss of control. The helicopter entered an uncommanded left turn that spanned approximately 540 degrees. The pilot eventually re-established control and executed a go-around procedure, entering the traffic circuit and landing safely without further incident. There were no injuries to the five occupants and no damage to the aircraft.
The investigation
CENIPA's investigation focused on the sequence of events during the low-speed taxiing maneuver. Investigators examined the flight crew's performance, the aircraft's technical state, and the environmental conditions. The investigation noted that the pilot in command (PIC) had not operated the aircraft from the left seat for an unspecified period of time.
Additionally, the investigation looked into the pilot's workload and attention, noting that the PIC was engaged in radio communications with another aircraft during the critical phase of the flight. The investigation also reviewed the aerodynamic implications of the maneuver, specifically the risks associated with operating at speeds below 30 knots, which can lead to unexpected yaw due to tail rotor effectiveness issues.