What happened
On December 29, 2012, an AS-350B3 helicopter, registration PP-BRJ, operated by the Rio de Janeiro Military Fire Department (CBMERJ), was conducting a rescue mission near Copacabana Beach, Rio de Janeiro. The aircraft took off from the Lagoa Private Helipad with a pilot in command and three special equipment operators on board.
While the aircraft was hovering over the sea, it experienced a sudden loss of engine power and a loss of main rotor rotation. The pilot was forced to execute an autorotation at a low altitude, resulting in a forced landing on the water. The impact caused substantial damage to the aircraft's structure and components due to seawater contact. Despite the emergency, all four occupants evacuated the submerged aircraft unharmed and were assisted by lifeguards who were also on board.
The investigation
CENIPA's investigation focused on the sudden loss of power. While the engine itself showed no mechanical evidence of failure, data from the Digital Electronic Control Unit (DECU) revealed that the engine was at IDLE at the moment of impact.
Investigators examined the TWIST GRIP engine power control system, which uses microswitches to send electrical signals to the DECU. The investigation found that the microswitch box was not properly sealed against water. Furthermore, the investigation identified that the aircraft had experienced previous electrical issues, such as a total loss of radio communication due to humidity, which had not been properly documented in the maintenance logs.
Findings
- Saltwater ingress through unsealed attachment points on the microswitch box caused electrolytic corrosion on the microswitches.
- This corrosion created an electrical path that triggered the 54K relay, sending an unintended IDLE signal to the DECU regardless of the pilot's actual twist grip position.
- Organizational culture issues contributed to the accident, as the operator failed to formally monitor and record previous technical breakdowns and maintenance interventions.
- Managerial oversight was noted because the lack of formal registration for previous malfunctions prevented the identification of a recurring risk pattern.
- The crew was not wearing life jackets during the operation, which increased the risk during the emergency evacuation.