What happened
On April 20, 2000, a Bell 206B helicopter, registration PT-HOZ, was conducting a power line inspection mission in the northern region of Rio de Janeiro. The flight, operated by Helirio Táxi Aéreo, included the pilot and two technicians from an electric utility company.
After refueling at a decommissioned airfield in Volta Redonda, the aircraft was flying at a low altitude and low airspeed (approximately 30 knots) to monitor transmission towers. As the aircraft approached a steep terrain elevation, the pilot attempted to climb by increasing collective pitch and lowering the nose to gain airspeed. During this maneuver, the aircraft experienced a loss of control, entered a right-hand turn, and collided with trees approximately 20 meters high. The impact resulted in one fatality among the passengers, while the pilot and the second passenger sustained minor injuries. The aircraft was destroyed.
The investigation
CENIPA investigators examined several hypotheses, including engine failure due to mechanical malfunction or fuel contamination. Technical analysis of the engine by Rolls Royce and fuel samples from the aircraft's tanks and filters showed no abnormalities in fuel quality. While a minor oscillation in the N1 turbine speed was detected during bench tests—linked to insufficient lubrication in the Power Turbine Governor (PTG)—engineers concluded this did not represent a loss of power.
The investigation focused on the aircraft's performance limits. At the time of the accident, the helicopter was operating at a density altitude of 3,800 feet with a total weight of approximately 2,980 lbs. According to the manufacturer's altitude-versus-weight charts, the maximum allowable weight for those conditions was roughly 2,880 lbs. Furthermore, the flight profile—low altitude and low airspeed—placed the aircraft within the "Dead Man's Curve," a high-risk flight regime where safe autorotation is difficult.
Findings
- The pilot exceeded the operational weight limits for the prevailing altitude and temperature.
- The pilot demonstrated poor judgment by attempting a high-power climb while operating within the aircraft's performance limitations.
- The flight profile involved flying at low speeds and altitudes that placed the aircraft in the manufacturer-recommended avoidance zone (the "Dead Man's Curve").
- The mission profile—inspecting power lines at low altitude—was inherently unsuitable for a single-engine helicopter.
- There was a lack of adequate flight planning regarding terrain and aircraft performance capabilities.
Safety action
- The operator was directed to implement internal mechanisms to prevent flights that exceed operational limits regarding weight, altitude, and terrain.
- The operator was instructed to improve refueling procedures to eliminate the use of precarious drum-based fueling methods.
- Safety authorities were tasked with disseminating the lessons learned from this accident to other operators performing similar power line inspection missions.