What happened
On September 28, 1996, a Sikorsky S-61N helicopter, registration PT-YAG, operated by Aeróleo Táxi Aéreo, was performing a transport mission from Maca and towards the S.C. LANCER (NS-9) drilling rig in the Campos Basin. The aircraft was carrying three crew members and 15 passengers.
During the final approach, while descending through 500 feet at a rate of 300 feet per minute, the crew heard a loud bang from the upper section of the aircraft. This was immediately followed by intense vibrations that rendered the helicopter completely uncontrollable. The aircraft struck the sea in a slightly nose-down and right-banked attitude. The helicopter remained afloat for approximately three hours before sinking to a depth of 720 meters.
The accident resulted in one fatality, one passenger reported missing, and several injuries. The pilot sustained serious injuries, the co-pilot sustained minor injuries, and among the passengers, one suffered serious injuries and 11 sustained minor injuries.
The investigation
CENIPA investigators examined the wreckage, which was recovered with the assistance of a remote-operated vehicle (ROV). Analysis of the Flight Data Recorder (FDR) revealed extreme accelerations in all axes, consistent with a major structural failure of the rotor system. Computer simulations confirmed the most probable scenario: the loss of approximately 90% of the mass of one rotor blade during flight.
Physical examination of the wreckage identified that the "red" blade (No. 1) had suffered a catastrophic failure. Investigators found a pre-existing crack near the leading edge of this blade. Furthermore, the investigation revealed evidence of unauthorized or improper rework on the blade, including sanding marks, irregularities in the paint, and primer found within the cracks. The investigation also noted that the aircraft had been exhibiting vibration issues for four months prior to the accident, and a safety report regarding these vibrations had been filed but not effectively addressed by the operator.
Findings
- In-flight structural failure: The primary cause of the accident was the loss of approximately 90% of the mass of the No. 1 rotor blade due to fatigue-induced failure.
- Deficient maintenance: The investigation identified inadequate maintenance practices, noting that cracks on the blade could have been detected had the paint been properly inspected or removed.
- Deficient supervision: The operator failed to take a conservative approach to reported malfunctions and did not act upon the safety reports regarding aircraft vibrations.
- Operational failures: During the emergency descent, the crew did not ensure all passengers were properly restrained; specifically, the fatal injury occurred because the deceased passenger was not wearing a seatbelt, leading to a fatal head impact during the water impact.
- Organizational issues: The operator's safety culture was compromised by a lack of effective communication regarding reported hazards and a failure to ground the aircraft despite known vibration issues.