What happened
On October 5, 1998, an HB-350B helicopter, registration PP-FJC, operated by the Secretaria de Segurança Pública do Distrito Federal, was conducting a test flight to verify the integrity of a recent engine oil reservoir weld. After an initial landing to confirm there were no leaks, the aircraft took off again for a low-level pass at approximately 15 meters above the runway at the APUB ultralight airfield.
During the maneuver, the pilot attempted to establish a landing pattern using a "teardrop" approach, executing a right-hand turn followed immediately by a left-hand descending turn. During this sequence, the pilot lost control of the aircraft. The helicopter entered a high rate of descent and struck the ground on a dirt road parallel to the runway. The impact caused significant damage to the tail cone and a loss of tail rotor pedal control. The aircraft continued to fly for approximately 500 meters before colliding with a fence at the Nelson Piquet Autodrome, where it came to rest on its right side.
The investigation
The CENIPA investigation established that the aircraft was in an airworthy condition but was operating under high-stress environmental conditions. The ambient temperature was 34°C at an altitude of 3,800 feet, which significantly reduced the available power margin. The investigation also found that the aircraft was carrying five occupants, despite the mission only requiring a pilot and a mechanic, which increased the takeoff weight to 1,886kg, nearing the maximum limit of 1,950kg.
Investigators examined the aerodynamic effects of the pilot's maneuvers, noting that the abrupt cyclic input during the turn caused a reduction in the vertical component of lift. Furthermore, the investigation highlighted significant organizational deficiencies within the operator's structure, noting a lack of formal flight training programs and inadequate supervision of flight operations.
Findings
- Improper Flight Maneuver: The pilot executed a teardrop traffic pattern that violated established special air traffic rules for helicopters.
- Aerodynamic Loss of Control: The abrupt banking of the rotor disk, combined with the "coning effect" during high-load maneuvering, led to a loss of lift and a high rate of sink.
- Excessive Weight: The presence of three unnecessary passengers increased the aircraft weight, leaving a very small margin for power recovery during the maneuver.
- Organizational Deficiencies: The operator lacked a formal pilot training program and failed to provide adequate oversight of flight safety and operational planning.
- Inadequate Recovery Technique: Following the initial impact, the pilot failed to maintain the recommended 70kt airspeed required for landing without tail rotor control.