What happened
On March 22, 1999, at approximately 09:26 local time, a Bell 206L-4 helicopter, registration PT-YAA, was conducting a low-altitude power line inspection mission near Ipatinga, Minas Gerais. The aircraft, operated by CEMIG, had previously stopped in Ipatinga to embark two technicians for the inspection of electrical infrastructure.
While flying along the power line corridor, the helicopter encountered a high-voltage line belonging to another utility company, CENIBRA, which crossed the inspection path at an approximately 90-degree angle. The aircraft struck these wires, which became entangled in the helicopter's wire cutters. Although the cutters eventually severed the line, the impact and entanglement caused the pilot to lose control of the aircraft. The helicopter subsequently struck the ground at Morro Caravelas, resulting in the three fatalities of the pilot and the two passengers.
The investigation
CENIPA's investigation focused on the operational conditions and the pilot's decision-making process. Investigators conducted a reconstruction flight along the same axis and direction as the accident. This reconstruction revealed that the sun was positioned directly in the pilot's forward field of view, creating significant glare that obscured the visibility of the crossing wires.
The investigation also examined the technical state of the aircraft and the infrastructure. The Bell 206L-4 was found to be in airworthy condition with all maintenance logs up to date. However, investigators noted that the intersection of the two power grids lacked the required visual signaling for aircraft, as mandated by Brazilian technical standards (ABNT NBR 6535). Furthermore, the investigation highlighted that the pilot had the option to perform the inspection in the opposite direction, which would have placed the sun behind the aircraft, significantly improving visibility.
Findings
- Improper flight planning: The pilot failed to account for the sun's position and its impact on visibility during the mission.
- Poor decision-making: The pilot chose to fly toward the sun rather than in the opposite direction, which would have mitigated the risk of obstacle collision.
- Environmental factors: The position of the sun directly in the aircraft's path caused a failure in perception, making the crossing wires nearly invisible.
- Lack of infrastructure marking: The power line intersection was not properly marked with the required aviation warning signals.
- Overconfidence: The pilot's extensive experience and familiarity with the area contributed to a lack of adequate attention to potential obstacles.
Safety action
- The Civil Aviation Department was tasked with requesting that the National Electric Energy Agency (ANEEL) ensure all utility companies comply with NBR 6535 regarding the installation of warning signals at power line intersections.
- Regional Safety Action Centers (SERAC) were directed to alert all power line inspection operators regarding the critical importance of mission planning, specifically regarding flight time, altitude, and sun position.
- CEMIG was instructed to train its pilots to adopt safety precautions that avoid flying in conditions where environmental factors, such as sun glare, unnecessarily increase operational risk.