NTSB Identification: WPR10FA133
14 CFR Part 91: General Aviation
Accident occurred Sunday, February 14, 2010 in Cave Creek, AZ
Probable Cause Approval Date: 11/07/2012
Aircraft: EUROCOPTER EC135, registration: N127TS
Injuries: 5 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
A ranch foreman who observed the flight preparations saw the helicopter owner board the helicopter through the left forward cockpit door and occupy the left front cockpit seat. The helicopter owner's 5-year old daughter also boarded the helicopter through the left forward cockpit door and sat on her father's lap. The pilot, who had accumulated 11,045 hours of total flight time, all in rotorcraft-helicopters, 824 hours of which were in the EC135 T1, was already seated in the right front cockpit seat. Both the left and right front cockpit seats were equipped with dual flight controls. Operator personnel revealed that the helicopter owner's daughter had sat on her father's lap occasionally during flights, that the owner liked to fly the helicopter, and that it was common for him to fly. Although the owner held a certificate for airplane single-engine land, he was not a rated helicopter pilot. However, it could not be determined who was flying the helicopter at the time of the accident.
About 35 minutes after departing the ranch, the helicopter approached an area about 1 nautical mile (nm) north of the accident site. Radar data revealed that the helicopter was about 2,000 feet above ground level (agl). Witnesses on the ground stated that they heard unusual popping or banging noises. Several witnesses also stated that they saw parts separate from the helicopter before it circled and dove to the ground. The helicopter impacted a river wash area north of the destination airport in a slightly nose-down and slightly left-bank attitude. The helicopter was subsequently consumed by a postcrash fire. The accident was not survivable.
A postaccident examination of the helicopter revealed that the yellow blade had impacted the left horizontal endplate and the tail rotor drive shaft in the area of the sixth hangar bearing, which resulted in the loss of control and subsequent impact with terrain. All of the damage at the aft end of the steel section of the tail rotor drive shaft was consistent with a single impact from the yellow main rotor blade. No preimpact failures or material anomalies were found in the wreckage and component examinations that could explain the divergence of the yellow blade from the plane of main rotor rotation. The most probable scenario to explain what caused the yellow blade to be in a position to strike the tail rotor drive shaft was that all of the main rotor blades were following a path that would have intersected the tail rotor drive shaft as a result of an abrupt and unusual control input. Further, witness marks that were on the tops of the blade cuffs likely occurred during the accident flight.
Flight simulation indicated that the only way that this condition could have occurred was as a result of a sudden lowering of the collective to near the lower stop, followed by a simultaneous reaction of nearly full-up collective and near full-aft cyclic control inputs. A helicopter pilot would not intentionally make such control movements.
A biomechanical study determined that it was feasible that the child passenger was seated on the helicopter owner's lap in the left front cockpit seat during the flight and that the child could fully depress the left-side collective control by stepping on it with her left foot. The child was estimated to weigh about 42 pounds at the time of the accident. The collective has a breakout force of between 2.2 and 3.1 pounds and would only need a maximum force of 5 pounds to fully move the control. Thus, the force to displace the collective fully was a maximum of 8.1 pounds, which is much less than the child's total weight and less than she would exert with her left foot if pushing to stand up from a seated position.
The biomechanical study also found that the collective lever's full range of motion was 9.5 inches from full up to full down and that the spacing between the left edge of the seat, the collective, and the door are sufficient such that a child's foot could rest on the collective and depress it. The study noted that the cyclic control could be moved to the full-aft position even with a small child of this size seated on the lap of an adult male in various positions.
Because the spacing between the upper partition, which separated the cockpit from the aft cabin compartment, and the ceiling was about 5 inches, it is unlikely that the child could shift from the left front cockpit seat to one of the rear seats during the flight.
Considering that the child was sitting on the owner's lap in the left front cockpit seat, it is highly likely that the child inadvertently stepped on the collective with her left foot and displaced it to the full down position. This condition would have then resulted in either the pilot or the helicopter owner raising the collective, followed by a full-aft input pull of the cyclic control and the subsequent main rotor departing the normal plane of rotation and striking the left endplate and the aft end of the tail rotor drive shaft.
During its investigation of this accident, the NTSB found that the pilot was involved in two incidents (in May 2003 and January 2004) while operating the accident helicopter; neither incident was reported to the Federal Aviation Administration. Of note, on May 8, 2003, the helicopter owner was operating the aircraft, and his seat slid aft while on final approach to landing. The helicopter dropped about 50 feet before impacting terrain, resulting in damage to the horizontal stabilizer. In this incident, the pilot failed to use proper cockpit discipline when he allowed the helicopter owner, who did not have a helicopter rating, to operate the helicopter's controls, particularly during a critical phase of flight. Further, an instructor pilot who conducted recurrent training for the accident pilot, reported that, during a conversation, the accident pilot commented to him about how the owner would dominate the cockpit duties, as he would get in the helicopter, flip the switches, and go.
Although it could not be determined who was flying the helicopter at the time of the accident (and it is not relevant to the cause of this accident), the previous incidents, the statement by the pilot that the helicopter owner dominated cockpit duties, and the pilot allowing the owner’s daughter to sit on his lap during flight together indicate that the pilot did not maintain strong cockpit discipline.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The sudden and inadvertent lowering of the collective to near the lower stop, followed by a simultaneous movement of the collective back up and the cyclic control to a nearly full-aft position, which resulted in the main rotor disc diverging from its normal plane of rotation and striking the tail rotor drive shaft and culminated in a loss of control and subsequent impact with terrain. Contributing to the accident was absence of proper cockpit discipline from the pilot. Full narrative available
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