Papillon Airways Airbus Helicopters EC 130 T2 accident

The helicopter was returning to the operating base following an air tour flight with six passengers. The helicopter entered a hover-taxi and the pilot initiated a slow left turn with a right crosswind of 11 knots, gusting to 20 kts. After the tail of the helicopter passed through the wind, the tail continued to swing to the right and the helicopter entered a climbing left spin. The pilot told investigators that when the helicopter started turning left, he applied right anti-torque pedal to stop the turn, and when the helicopter continued to spin left, he lowered the cyclic. The helicopter completed about 3 full left turns before descending rapidly and impacting the ground. The helicopter fuselage was substantially damaged, and 5 passengers and the pilot were seriously injured. The helicopter was equipped with an Engine Data Recorder (EDR) that stored pedal potentiometer (position) values and airport security video captured the accident sequence. The data and video evidence are consistent with the pilot initiating a left pedal turn by applying about 1/3 left pedal input (from neutral). After about 90° of heading change, as the tail passed through the wind line, the pilot applied about 3/4 right pedal input followed by reversal to 2/3 left pedal input (in the direction of rotation). The pilot then applied 1/2 - 3/4 right pedal input as he rapidly lowered the collective. The accident helicopter was equipped with an anti-torque Fenestron. Airbus Helicopters published an Information Bulletin that outlines the differing performance characteristics of a Fenestron-equipped helicopter compared to a helicopter with a conventional tail rotor (CTR). As outlined in the bulletin, on a CTR-equipped helicopter the thrust curve is more linear when compared to a Fenestron-equipped helicopter. The effect of a control input with a CTR is almost constant throughout the whole pedal range, while it significantly varies for the Fenestron. The thrust curve slope is larger, and thus the perceived efficiency of the Fenestron is greater, when coming close to the full left pedal stop. An Airbus Helicopters Safety Information Notice regarding unanticipated left yaw states “… use of the rudder pedal … may not cause the yaw to immediately subside, thus causing the pilot to make inadequate use of the pedal to correct the situation because he suspects that it is ineffective when, in fact, thrust capability of the tail rotor available to him remains undiminished.” “The key feature of an unanticipated left yaw recovery is large amplitude right pedal input. Recovery may not be immediate but will occur if the pilot persists in maintaining right pedal. In some instances, the pilot re-centered the pedal before entering again a right pedal input. This cannot help and only delays recovery from the yaw. If the yaw deceleration is not enough, more right pedal must be added, reaching the pedal end-stop if necessary.” The evidence indicates that when the pilot initiated the left hover-taxi turn he failed to apply right anti-torque pedal in a sufficient and timely manner to arrest the left turn. The helicopter subsequently entered an uncontrolled spin before impacting the ground. Six of the seven occupants received serious injuries attributable to the hard landing. The seats installed in the helicopter were equipped with energy-absorbing devices designed to reduce occupant injuries in the event of a hard landing and had been certified to standards established by the European Aviation Safety Agency (EASA) and the United States Code of Federal Regulations (CFR). Examination of the seats showed inconsistencies in the performance of the energy-absorbing devices. Measurements were taken, and it was noted that the seats did not stroke as expected when compared with the occupant’s overall stature. Energy-attenuating seats are designed to stroke to absorb an occupant’s energy, and the amount of stroke would vary based upon the weight of each occupant. In this accident there were occupants close to the size of a 50th percentile male used in certification; however, the seats did not stroke as expected. Additionally, there were larger occupants whose seats did not stroke at all, which likely contributed to the severity of the injuries of some of the occupants. A previous hard landing accident involving the same model helicopter and seats resulted in similar seat performance and occupant injuries. Those injuries were attributed to improper tightening and positioning of the seat restraints, which allowed the occupant’s positions in the seat to vary and affect the performance of the seats. Investigators could not determine if the occupant’s seat restraints were properly tightened and positioned in this accident. Performance studies of the accident determined the helicopter and the seats were subject to high lateral forces at impact as the helicopter rotated and the seat manufacturer stated the inconsistent performance of the seats was likely due to the lateral forces encountered; however neither the EASA or CFR certification standards specified lateral force testing. No anomalies were noted with the seats or energy-absorption devices during postaccident examination that would have contributed to their inconsistent performance. Therefore, the seat’s energy-absorbing devices likely performed inconsistently due to the lateral rotational forces encountered during the accident which were not required to be accounted for during the certification process.

Verbatim NTSB analysis and probable cause from the NTSB dataset