History of Flight
On January 2, 2013, at 2057 central standard time, a Bell Helicopter model 407, registration N445MT, struck the ground in a harvested agricultural field near Clear Lake, Iowa. The helicopter, owned by Suntrust Equipment Leasing & Finance Corporation and operated by Med-Trans Corporation, was conducting a positioning flight under 14 Code of Federal Regulations Part 91, though it operated on a company flight plan in accordance with Part 135. Night visual meteorological conditions prevailed; no flight plan was filed with the Federal Aviation Administration. The flight had departed Mercy Medical Center in Mason City, Iowa, about 2049, en route to Palo Alto County Hospital (IA76) in Emmetsburg, Iowa.
A witness about 1 mile south of the accident site observed the helicopter approaching from the east. It appeared to slow and turn north, then descended straight down. He described the weather as "misty" with light wind. Another witness heard the helicopter's sound change as if turning, followed by a "thump." He noted ice on his truck windshield that wipers could not clear and observed a police car slide through an intersection while responding. A pilot at Mason City Municipal Airport (MCW) saw the helicopter at an estimated 300 feet above ground level; he noted glaze ice on his car and had encountered light rime ice earlier while flying through a cloud.
GPS tracking data showed the helicopter at the medical center at 2049:44. It proceeded westbound at about 1,800 feet mean sea level (msl), passed south of MCW at 2052:44, entered a right turn to a northbound course about 2056:09, and climbed to about 2,995 feet msl at 2057:04. During the climb, it entered a left turn to a southbound course. The final data point at 2057:14 was about 774 feet north of the accident site at 2,723 feet msl. The field elevation of MCW is 1,214 feet.
The main wreckage came to rest along a line of trees and bushes. The debris path was about 100 feet long oriented on a 246-degree magnetic bearing.
Personnel Information
The pilot held an airline transport pilot certificate with helicopter and single-engine airplane ratings, with airplane privileges limited to private. He held a second-class medical certificate dated April 17, 2012, requiring corrective lenses. He completed the operator's new hire training on September 24, 2012, and night vision goggle (NVG) training on September 27, 2014. His Part 135 checkride was on September 29, 2012, and base training on October 5, 2012. At initial employment, he reported 2,808 total flight hours, including 2,720 in helicopters and 248 at night. Duty records showed 3.7 flight hours in October (all daylight), 9.9 hours in November (3.1 night with NVGs), and 5.6 hours in December (5.4 night with NVGs). His most recent flight was December 21, 2012. He was on duty for 12 hours the day before the accident without logging flight time, and reported for duty at 1820 on the accident day.
Aircraft Information
The accident helicopter, Bell Model 407 serial number 53959, was configured for helicopter emergency medical services (HEMS). The FAA type certificate required one pilot and permitted day or night VFR operations. The helicopter was not certificated for intentional flight into known icing conditions or for instrument flight rules (IFR), though it had instrument flight equipment. It had heated pitot and static ports but no rotor blade ice protection. The Rolls-Royce Allison 250-C47B engine (serial number CAE-847212) had maximum takeoff power of 650 shaft horsepower and maximum continuous power of 600. The helicopter received a normal category standard airworthiness certificate in June 2009; it was purchased by Sun Trust Equipment Finance on April 29, 2010, and leased by Med-Trans. Maintenance was under an approved inspection program; the most recent inspection was on December 28, 2012, at 952.2 hours. Total time at the accident was about 956 hours. No outstanding maintenance discrepancies were noted. The engine anti-ice system, controlled by a switch on the overhead panel, routes hot air to the compressor guide vanes when activated; loss of electrical power automatically activates it.
Meteorological Information
At 2053, MCW ASOS reported wind 300° at 8 knots, 8 miles visibility, broken clouds at 1,700 feet agl, overcast at 3,300 feet, temperature -3°C, dew point -5°C, altimeter 30.05 inHg. Conditions worsened over time: at 2105, wind 310° at 10 knots, broken 1,500 feet, overcast 2,000 feet; at 2110, overcast 1,500 feet. Forest City AWOS (8 miles northwest) at 2055 reported wind 300° at 9 knots, 10 miles visibility, overcast 1,000 feet, temperature -2°C, dew point -3°C, altimeter 30.04 inHg. A 1955 observation included unknown freezing precipitation but was not repeated. MCW terminal forecast at 1959 expected wind 250° at 6 knots, 5 miles visibility in light snow, overcast 1,400 feet. Satellite imagery showed overcast stratiform clouds with tops near 11,000 feet. Radar showed no significant echoes, but the scan sampled from about 6,630 to 15,100 feet, missing lower levels. Pilot reports indicated light to moderate rime ice from 3,500 to 8,500 feet msl across Iowa; the closest was 70 miles west. AIRMET Zulu for moderate icing below 10,000 feet was current. Witnesses reported mist, drizzle, and icy roads.
Wreckage and Impact Information
The helicopter impacted a harvested field. Wreckage was fragmented; cockpit and cabin were compromised. A postimpact fire occurred. Main wreckage included main rotor blades, transmission, engine, fuselage portions, and tail boom. The tail rotor separated and was 80 feet east-northeast. Landing skids separated; left skid at initial impact point, right skid 35 feet west of main wreckage. Main rotor blades remained attached to hub but showed bending and delamination. Pitch change links and one pitch change horn separated from overstress. Transmission rotated freely; freewheeling unit shaft fractured at main and tail rotor drive splines from overstress. Flight control system fragmented; control tube separations consistent with overstress. Hydraulic actuator servos secured but deformed. Tail boom separated forward end, straight but deformed at ends. Tail rotor assembly separated; blades deformed but attached. Driveshaft separated near horizontal stabilizer consistent with main rotor strike. Engine examined under NTSB supervision showed deformation from impact; compressor impeller and turbine rotors exhibited rubs from rotation at impact. No preimpact failure or malfunction anomalies were observed.
Additional Information
Examination of caution and warning panel light bulb filaments showed stretching in cyclic centering, engine anti-ice, engine overspeed, and hydraulic system filaments, consistent with illumination at impact. The cyclic centering light illuminates when helicopter is on ground and cyclic not centered; engine anti-ice when activated; overspeed when detected; hydraulic when pressure below 650 psi. Normal hydraulic pressure is 1,000 psi.
Medical and Pathological Information
An autopsy attributed the pilot's death to multiple blunt force injuries from the accident. FAA toxicology tests were negative for all screened substances.
Tests and Research
The engine control unit (ECU) model EMC-35R was examined. Non-volatile memory from primary and reversionary governors was downloaded; total ECU time was 1,196.80 hours, engine time 1,003.06 hours. No continuous recording; only fault and incident data. Last engine run fault files showed no codes. Reversionary governor had 21 faults, the most recent at 733 ECU hours (270 hours before accident). Three snapshot incidents were recorded: first at 1,003:06:16.344 with 110% engine torque (pre-event data normal); second at 1,003:06:22.873 with 108% power turbine (overspeed event) and reduced collective and fuel flow; third at 1,003:06:22.920 with 109% rotor speed. Loss of subsequent data consistent with power loss at impact. The overspeed events with decreasing fuel flow and collective indicated aerodynamic driving of rotor above 100% during descent.