What happened
On September 9, 1999, a Bell 206 B3 helicopter, registration PT-HPQ, operated by Líder Táxi Aéreo Ltda, crashed into the Guarapiranga Reservoir in São Paulo. The flight had departed from Congonhas Airport (SBSP) to perform vibration and tuning tests on the main rotor. On board were the pilot and three passengers.
During the execution of a "Latch Down" procedure—a controlled descent at 60 knots with a constant rate of 1,000 feet per minute—the pilot experienced a significant optical illusion. Because the sun was setting, the water surface created a mirror-like reflection. This phenomenon caused the pilot to suffer spatial disorientation, leading him to believe the aircraft was at a higher altitude than it actually was. While momentarily diverting attention to engine instruments, the pilot failed to monitor the descent rate. Upon realizing the proximity to the water, the pilot attempted a recovery maneuver, but it was too late to prevent the aircraft from impacting the water.
The impact caused the tail rotor, fuselage, transmission shaft, engine, and main rotor to sustain severe damage, rendering the aircraft a total loss. All four occupants sustained minor injuries and were rescued from the submerged aircraft by a passing fishing club boat.
The investigation
CENIPA's investigation focused on the environmental conditions and the pilot's decision-making. The investigation established that the pilot was experienced and held a valid technical rating, although his IFR certificate had expired. The aircraft's maintenance was up to date, and the center of gravity was within limits.
Investigators examined the impact of the sunset, noting that the sun's position created a "mirror effect" on the reservoir, which is a known hazard for depth perception over water. The investigation also noted that the flight carried three passengers who were not directly involved in the maintenance tests, which was contrary to established regulations. Furthermore, the pilot was reportedly under high levels of professional stress due to intense work responsibilities within the company.
Findings
- Spatial disorientation caused by visual illusions from the sun reflecting off the water surface.
- Inadequate flight planning, as the chosen time and location presented high risks of optical illusions.
- Deficient judgment regarding the altitude required to safely complete the autorotation procedure.
- Environmental factors, specifically the sunset creating a mirror effect on the water, which obscured depth perception.
- Lack of specialized infrastructure, noting the absence of a dedicated, safe area for helicopter training and testing in the São Paulo region.
Safety action
- Líder Táxi Aéreo Ltda was directed to establish specific procedures for all experience flights, defining safe locations, times, and protocols.
- The São Paulo Air Traffic Service (SRPV-SP) was tasked with studying the possibility of demarcating a specific area for helicopter testing and training.
- The Department of Civil Aviation (DAC) was instructed to disseminate information regarding this accident to helicopter operators to increase awareness of environmental risks during training flights.