What happened
On April 25, 2001, an HB-350B helicopter, registration PT-HNO, was conducting a local instructional flight at Jacarepaguá Aerodrome (SBJR) in Rio de Janeiro. The crew, consisting of an instructor, a student, and two additional passengers, was performing a simulated hydraulic system failure training maneuver involving a running landing on a grass area.
During the approach, the student pilot experienced difficulty maintaining directional control, with the aircraft's nose drifting to the right. As the aircraft touched down on the uneven grass surface, a strong vibration was felt, which the crew misinterpreted as resonance. In an attempt to stabilize the aircraft, the student lowered the collective. The instructor then took control to execute a go-around. However, during this maneuver, the increased torque caused a significant leftward yaw. The aircraft entered a series of turns, eventually losing control and colliding with the ground. All four occupants escaped the crash without injury, though the aircraft sustained severe damage.
The investigation
CENIPA's investigation focused on the execution of the emergency simulation and the crew's response to the aircraft's behavior. The investigation examined the flight profiles, the condition of the landing area, and the proficiency of the pilots. Investigators noted that while the HB-350B remains controllable without hydraulic assistance, the controls become significantly heavier and require greater anticipation and larger control inputs. The investigation also reviewed the lack of a formal pre-flight briefing and the suitability of the training site, which featured uneven terrain.
Findings
- Improper control inputs: The student pilot failed to use adequate pedal inputs to counteract torque variations, leading to a misalignment of the aircraft's longitudinal axis.
- Misinterpretation of aircraft behavior: The crew incorrectly identified heavy vibrations during the landing roll as resonance, leading to improper collective adjustments.
- Delayed instructor intervention: The instructor did not assume control until the situation had become critical, allowing the unaligned touchdown to occur.
- Inadequate flight planning: The landing site was chosen based on an arbitrary decision to avoid uneven ground in another section, rather than a technical analysis of the terrain.
- Instructional deficiencies: There was no evidence of a pre-flight briefing, and the instructor's proficiency in flight instruction was found to be lacking despite high flight hours.
- Training environment: The grass area used for the running landing was not in optimal condition for such maneuvers.