History of Flight
On October 24, 2015, at 1633 Pacific daylight time, an American Eurocopter AS350B3 helicopter, N911WL, landed hard during a practice autorotation near Folsom, California. The flight instructor, pilot undergoing instruction (PUI), and tactical flight officer (TFO) were not injured; the helicopter sustained substantial damage. The helicopter was registered to Placer County and operated by the Placer County Sheriff's Department as a public aircraft flight. Visual meteorological conditions prevailed, and a company flight plan had been filed. The instructional flight departed from McClellan Airfield, Sacramento, California, at 1618.
The purpose of the flight was to perform patrol missions and provide training for the PUI, who had recently been hired. This was his first patrol training flight, and he was seated in the front left seat, with the flight instructor in the front right, and the TFO in the rear jump seat. The plan was to introduce the PUI to the helicopter's systems while on patrol and then perform a series of straight-in, 180°, and enhanced autorotations. The flight instructor described an enhanced autorotation as a maneuver where a point is picked for an emergency landing, and the pilot is tasked with landing the helicopter at that point using whatever maneuvers are necessary.
The crew departed from their base at Auburn Municipal Airport about 1230 for routine patrol work. They then transitioned to a series of autorotations with power recoveries in a flat field, all uneventful. They landed at McClellan Airfield and serviced the helicopter with about 120 gallons of fuel. After departure, they flew to a peninsula on the northern shore of Folsom Lake Reservoir to perform more enhanced autorotation training. The peninsula, normally partially submerged, was fully exposed due to drought conditions.
They surveyed the area and began the maneuver at 2,500 ft mean sea level (about 2,100 ft above the lake surface). The flight instructor stated that he was pilot-in-command and that the PUI was shadowing the controls. They performed an enhanced autorotation with a power recovery to the dry lakebed, during which the PUI appeared overwhelmed. They set up for another approach, and the flight instructor instructed the PUI to track rotor RPM and not worry about foot pedals or attitude, demonstrating that rotor RPM could be controlled with cyclic and collective.
At about 1,000 ft agl, the flight instructor felt the PUI inadvertently hindering the controls and moved his hands away. He was not concerned, as this was not unusual during training. Rotor RPM remained within limits during the descent. As they approached 100 ft agl, the flight instructor verbalized his intention to perform a power recovery, turning the throttle twist grip from idle to flight while initiating a flare. He did not hear the engine fully regain speed and observed the engine and rotor RPM needles were split. Between 10 and 25 ft from the ground, he prepared for a touchdown landing but the helicopter had moved to down-sloping terrain. He aimed to touch down flat on the skids relative to the slope and pulled the collective hard just before impact to cushion the landing. The engine then recovered to full speed, and he applied collective to lift the helicopter off the ground, maneuvering to land about 100 ft forward.
After landing, he exited and discovered the aft airframe wrinkled and the tailboom bent downwards at the intersection with the aft bulkhead. He was surprised, as the landing did not feel hard enough to cause structural damage. He recounted performing many autorotations without anomalies and that the engine sound did not match his throttle inputs. During the autorotation, he focused on audio and visual external clues rather than instruments. He did not hear any audible alerts or notice annunciator panel lights; all gauges were in the green.
The PUI recounted similar observations. He agreed that the flight instructor would fly the final autorotation while he shadowed the controls. During the descent, he kept his right hand on his lap and lightly held the collective. At one point, the cyclic brushed his hand, and the flight instructor asked what he was doing and moved his hand to his lap. There was no interference with flight controls. As they approached 100 ft agl, the flight instructor stated he was applying throttle; the PUI felt the twist grip move and released his hand. As they approached the hilltop landing spot, the flight instructor initiated the flare. The PUI had a sensation that something was wrong; he felt he should sense power being applied but did not. At about 20 ft agl, terrain fell away, and he heard a change in engine tone, then the helicopter sank rapidly. He saw the flight instructor pull up on the collective, and the helicopter landed hard, tipping forward. It then lifted back into the air under power.
Personnel Information
The flight instructor had been with the air support unit since 2000 as the chief and only helicopter pilot. He attended training at Airbus four times since 2009, most recently in May 2014. He held a commercial pilot certificate and flight instructor certificate with helicopter ratings, reporting 5,580 total helicopter hours, 1,658 in the AS350B3.
The PUI held a commercial pilot certificate with ratings for airplane single-engine land, helicopter, instrument airplane, and instrument helicopter, and a type rating for the Sikorsky S-65 (CH-53) helicopter. He reported 1,341.8 total flight hours, 12.2 in the AS350 series. The accident flight was his first autorotation training in the AS350.
Aircraft Information
The helicopter, call sign Falcon 30, was manufactured in 2008 and equipped with a Turbomeca Arriel 2B1 engine. It was maintained under a continuous airworthiness program; the last inspection was on October 9, 2015, 9.3 flight hours prior. It was equipped with the Airbus Helicopters maximum gross weight increase kit, including high skid landing gear and dual hydraulic system, giving a maximum internal gross weight of 5,225 pounds. According to the flight instructor, the helicopter weighed 5,166 pounds at the time.
Testing and Research
Post-accident examination of the twist grip confirmed functional and logical operation and compliance with service bulletins. No corrosion to microswitches or contacts was observed. The engine and digital engine control unit were examined and tested; the engine performed to nominal specifications, and the DECU passed self-test. Historical data showed no faults attributed to the accident flight. Data from the helicopter's mapping system revealed a flight track closely matching the pilots' statements.
Medical Information
The flight instructor's second-class medical certificate was suspended due to Type 1 diabetes. The department was aware and required him to show glucose levels throughout the day. He was only allowed to fly with a safety pilot on board. He was subsequently issued a third-class medical certificate in August 2017. He was awake and alert during and after the accident.