History of Flight
On December 15, 2015, about 1723 mountain standard time, an Airbus AS350 B3 helicopter, registration N74317, was substantially damaged when it impacted terrain while maneuvering near Superior, Arizona. The helicopter was registered to and operated by Air Methods Corporation, doing business as Native Air Ambulance, under Title 14 Code of Federal Regulations Part 135. The commercial pilot and flight nurse sustained fatal injuries; the flight paramedic sustained serious injuries. Visual meteorological conditions prevailed, and a company VFR flight plan was filed for the repositioning flight. The cross-country flight originated about 1708 from Phoenix-Mesa Gateway Airport (IWA), Mesa, Arizona, with an intended destination of Globe, Arizona.
According to the operator, the helicopter was based in Globe and had transported a patient from Cobre Valley Community Hospital in Globe to Baywood Heart Hospital in Mesa. After transporting the patient, the pilot flew to IWA for refueling before the return flight to Globe. The flight paramedic stated that after refueling, they departed IWA and headed east toward the Superstition Mountains.
Local radar and flight data from an onboard Appareo GAU2000 data logger showed the helicopter departed IWA about 1708 and headed east-northeast maintaining about 500 feet above ground level (agl). The helicopter made a 360° right turn over Gold Canyon at 1715. According to the flight paramedic, the flight nurse's daughter was outside her house waving as they flew by at 400-500 ft agl. Over the next 4 minutes, the flight track continued east along the south side of the Superstition Mountains at or below 500 ft agl.
About 1719, the helicopter entered mountainous terrain, and its height above terrain varied as terrain elevation changed. Between 1718 and 1720, altitude varied between 240 ft agl and 1,150 ft agl. Between 1720 and the end of the flight, altitude varied between 30 ft agl and 770 ft agl. About 1721, the helicopter turned from a heading of about 80° to about 45° and followed a canyon beneath ridgelines. It flew nearly perpendicularly over Rogers Canyon, and at 1723:07, it continued through a saddle, clearing terrain by about 30 ft. As it passed over the eastern ridgeline, it banked right, changing ground track from about 43° to 76°, reaching a ground speed of about 120 knots. After clearing the ridge, it descended and accelerated to a maximum ground speed of 148 knots at 1723:21. It banked right (about 5° to 10° roll), and heading changed from 76° at 1723:18 to about 90° at 1723:32.
At 1723:32, the GAU2000 recorded an abrupt increase in pitch rate and right roll rate, consistent with right and aft cyclic inputs. According to the paramedic, the pilot said an expletive in a panicked voice. The paramedic looked up and saw a ridgeline immediately in their flight path and terrain filling the view. He described subsequent motions as a violent hard right bank, and the pilot made jerky fast hand movements. The helicopter impacted terrain on the northwest facing slope of a ridgeline near a saddle, at about 5,035 ft mean sea level.
Personal Information
The pilot, age 51, held commercial pilot and flight instructor certificates with rotorcraft-helicopter rating. His most recent FAA second-class medical certificate was issued December 8, 2015, with the limitation that he must have available glasses for near vision. He had accumulated about 5,670 hours of flight experience, with about 2,117 hours in the same make and model. He completed initial company training in September 2014 and his most recent annual 14 CFR 135.293 and 135.299 check on August 22, 2015. The paramedic stated the pilot was the safety officer at the Globe base and took the job seriously. He said the pilot flew lower than other pilots but was never dangerously low, and he did not think the pilot took risks or operated dangerously.
Aircraft Information
The helicopter, serial number 4317, was manufactured in March 2007 and had accumulated about 4,236 flight hours. It was equipped with a Turbomeca Arriel 2B1 turboshaft engine with about 2,491 hours. The helicopter's weight at the time of the accident was about 4,801 pounds, less than the maximum gross weight of 4,961 pounds. It was maintained under an FAA-approved inspection program. Recent maintenance included a daily check of tail rotor laminated half bearings on December 15, a 10-hour inspection on December 14, and multiple inspections on December 10.
The helicopter was equipped with an Artex C406-N HM ELT, manufactured October 2007, installed in May 2008. The ELT battery was installed in May 2015; the last maintenance check per 14 CFR 91.207(d) occurred on October 29, 2015. The ELT did not activate during the accident sequence but activated when wreckage was moved.
The Airbus AS350 B3 has a single hydraulic system providing 600-psi boost to cyclic, collective, and tail rotor controls. The main rotor control system uses rigid rods interconnected by bell cranks and reversing levers, interfacing with the swash plate through three hydraulic servo actuators. If required control force exceeds available servo pressure, the hydraulic system reaches its limitation, and the pilot must supply remaining force, felt as control stiffening. This phenomenon is called servo transparency, also known as hydraulic transparency, servo reversibility, or jack stall. The NTSB examined servo transparency during a 2003 accident investigation (LAX03MA292) and produced a study describing it as a condition when rotor system forces overcome hydraulic actuator capability, transmitting feedback to pilot controls. Eurocopter published Service Letter No. 1648-29-03 in December 2003 advising pilots about the phenomenon. The FAA issued a Special Airworthiness Information Bulletin in January 2004. After this accident, Airbus Helicopters issued Safety Information Notices 3093-S-00 (October 2016) and 3287-S-67 (November 2018) discussing operational precautions and servo transparency.
Meteorological Information
At 1715, weather at Coolidge Municipal Airport (P08), about 38 miles south-southwest of the accident site, reported wind from 310° at 5 knots, sky clear, temperature 9°C, dew point -4°C, altimeter 29.99 inches of mercury. Density altitude at the accident site (5,037 ft) was about 5,089 ft. At 1647, weather at Phoenix-Mesa Gateway Airport reported wind from 300° at 5 knots, visibility 45 miles, few clouds at 7,000 ft msl, temperature 11°C, dew point -5°C, altimeter 30.00 inches. Sunset was at 1718; civil twilight ended at 1746; moonset was at 2152. At 1730, the sun was -3.0° below the horizon at azimuth 243.9°; the moon was 40.5° above the horizon as a waxing crescent with 20% illumination.
Wreckage and Impact Information
The accident site was in mountainous terrain about 18 miles west of the Globe base, with surrounding peaks at 5,700-6,000 ft. The debris field was about 330 ft long on a magnetic heading of about 230°. First identified points of contact were multiple cuts through two bushes about 2 ft apart, cut at about 45° to the horizon. Downhill, four divots in soil, each about 18 inches long, 12 inches wide, and 3 inches deep, spanned about 20 ft. These were consistent with main rotor blade strikes. Fragments of rotor blade material were found. About 62 ft from the main rotor strikes was a shallow elongated crater (1 ft wide, 3 ft long) with broken branches and the helicopter's right step and forward right toe skid. The debris path continued 64 ft to the tail rotor assembly. Midway, helicopter doors, right engine cowling, interior paneling, gurney, and medic bag were found. About 5 ft further were two helmets. About 10 ft from helmets were left step and forward left toe skid. The fuselage came to rest on its right side about 40 ft downslope from the tail rotor assembly. Cabin roof sections were near the fuselage. The forward cabin floor separated; the fuselage forward of forward skid mounting legs bent upward about 30°. The pilot's seat remained attached; floor structure and seat rails were buckled. The rear cabin modular seating system separated; two right seats remained attached to the lower support bracket, seat bottoms separated, seat belt buckles unlatched. The left seat separated; its bottom was near the main rotor hub, belt unbuckled and webbing wrapped around the main rotor head. The engine was exposed and separated from drive shafts, remained attached to fuselage, crushed and distorted at exhaust. Main rotor hub and blades remained attached, with deformation and delamination from mid-sections to tips; yellow blade frayed at tip. Tail boom partially attached. Fuel tank right side visible and intact; fuel leaked during examination. Ground downslope saturated in fuel. Instrument console separated and found in a tree about 200 ft down debris. Tail rotor blades had minor damage; tail rotor system rotated freely. The ELT remained attached and undamaged, activated when wreckage moved.
Medical and Pathological Information
The pilot's autopsy reported cause of death as multiple blunt force injuries. A cavernous hemangioma (3x2.5x2.5 cm) was found in the left temporal/occipital lobe; no bleeding or acute findings associated with it. No other natural disease identified. Toxicology was negative for carbon monoxide and ethanol; metoprolol (used for hypertension) was detected. The flight nurse's injuries included multiple rib fractures with left flail chest and intraabdominal bleeding (1300 cc total); Injury Severity Score was 22.
Survival Aspects
The paramedic stated he never lost consciousness and came to rest suspended by his seatbelt harness. He cut himself free and slid to the snow. He heard the pilot take his last breaths. The flight nurse said he was pinned under the right skid and asked for help, but the paramedic could not move due to injuries. The paramedic was soaked in fuel and feared fire. Fuel poured from wreckage. The paramedic and nurse tried cell phones but had no reception.