Accident History
On May 10, 2008, at approximately 2237 central daylight time, a Eurocopter Deutschland GmbH EC 135 T2+ helicopter (registration N135UW) operated by Air Methods Corporation was destroyed after colliding with trees and terrain near La Crosse, Wisconsin. The flight was conducted under 14 CFR Part 91 without a filed flight plan. Night visual meteorological conditions prevailed at the accident site. The helicopter departed La Crosse Municipal Airport at 2234 bound for the University of Wisconsin Hospital heliport in Madison.
According to GPS tracking data, the helicopter had earlier transported a patient from Prairie du Chien to La Crosse, refueled, and then departed LSE. No further position updates were received after departure. A line service technician who fueled the helicopter reported that the weather included a low ceiling and moderate rain. A witness about 4.2 miles east-southeast of LSE heard the helicopter flying low and fast, and expressed concern about clearing the bluffs. Another witness reported the engine sound ceased followed by a loud crash. Local authorities initiated a search and the wreckage was located the next morning at about 0826.
Flight Crew and Operator
The pilot, aged 39, held a Commercial Pilot certificate with multiple ratings and a Second-Class Medical certificate with corrective lenses. He had accumulated 4,003 total flight hours, including 2,741 hours in rotorcraft and 121 hours in EC135 helicopters. His night flight time was 545 hours, and instrument time 216 hours. In the 90 days prior to the accident, he flew 49 hours in EC135s. However, his recent instrument experience was minimal: only 0.4 hours of actual instrument flight time in the preceding 12 months. The operator noted that the pilot had not completed an instrument proficiency check and was therefore limited to visual flight rules (VFR) operations under the Air Methods certificate. The pilot had previously been employed as a mechanic and transitioned to full-time pilot in 2005. He had made only two flights to the La Crosse area prior to the accident flight.
Aircraft and Maintenance
The accident aircraft was a 2007 Eurocopter EC 135 T2+ (serial number 0535) powered by two Turbomeca Arrius 2B2 engines. It had accumulated 456.7 total flight hours. The helicopter was maintained under an FAA Approved Inspection Program; the most recent checks found no discrepancies except for a main rotor blade crack that was replaced, and a landing light issue that was repaired before the accident. The helicopter was equipped with a radar altimeter but not a terrain awareness warning system, which was not required. Weight and balance calculations indicated the helicopter was within operating limits.
Weather Conditions
The National Weather Service charts indicated marginal VFR conditions along the route, with an area of IFR conditions near the accident site. The La Crosse ASOS reported light rain and mist, with ceilings as low as 1,300 feet. The Area Forecast warned of IFR conditions possible after midnight. The pilot received a weather briefing at 2117, which included information about AIRMET Sierra warning of IFR conditions southwest of the route. Another EMS pilot in the area reported fog forming on bluffs and declined additional flights due to deteriorating weather. Sunset was at 2019, and the moon was in a waxing crescent phase.
Wreckage Examination
The helicopter struck trees along a wooded ridgeline about 4.5 miles southeast of LSE. The initial impact was at tree-top level at an elevation of approximately 1,164 feet. The main wreckage came to rest about 600 feet further down the east side of the ridge at 928 feet. The tail boom and fenestron separated. The cockpit and cabin were heavily damaged. Examination of the engines showed debris ingestion and impact damage. The left engine power turbine blades sheared off, while the right engine blades remained intact. The cockpit engine control panel showed the left engine selector in IDLE and the right in FLIGHT, with switch guards engaged. The FADEC switches were on. Both engine mode selectors were in NORM.
Tests and Research
The Digital Engine Control Units (DECUs) were examined. The left DECU had a bent pin on the J2 connector (pin #14) that provided an OEI 30-second indication, but the manufacturer stated this did not affect engine control. The DECUs recorded an overspeed event on the right engine (117.69% N2) and a maintenance event on the left (117.81% N2) at 6.8 minutes after power-up, both in Flight Mode. The Vehicle Engine Multifunction Display (VEMD) recorded fault messages starting at 3 minutes 20 seconds flight duration, including loss of reliable torque, static pressure, and outside air temperature data, followed by a FADEC failure message and a DECU link failure at 3 minutes 24.5 seconds. The Caution Advisory Display recorded a single fault related to fuel tank sensor power supply at 3 minutes 24 seconds.
Additional Information
The operator's General Operations Manual required a minimum of 500 feet AGL and 1,000-foot ceiling with 5 miles visibility for night VFR operations. The maximum elevation figure for the La Crosse area was 2,200 feet MSL. At the estimated gross mass of 2,830 kg, the helicopter's rate of climb with both engines operating exceeded 1,200 feet per minute; with one engine inoperative at maximum continuous power, the rate of climb was about 260 feet per minute at 65 knots.