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NTSB Identification: CHI04FA214

On August 6, 2004, at 1959 central daylight time, a Eurocopter EC130 B4 helicopter, N450CM, piloted by a commercial pilot, was destroyed during an in-flight collision with a single-family residence and a post-impact fire near Prairie du Sac, Wisconsin. The personal flight was being conducted under 14 CFR Part 91 without a flight plan. Visual meteorological conditions prevailed at the time. The pilot and pilot-rated passenger sustained fatal injuries. One person in the residence sustained minor injuries. The flight departed the Rochester International Airport (RST), Rochester, Minnesota, approximately 1858.

Records indicate that on the day of the accident, the accident pilot departed Billings, Montana (BIL), and flew to Belle Fourche, South Dakota (EFC), Huron, South Dakota (HON), and to Rochester, Minnesota (RST).

An acquaintance of the pilot reported that the intended destination for the accident flight was Milwaukee, Wisconsin. She noted that the pilot was on a tour of the United States.

The Sauk County Sheriff's Department conducted witness interviews after the accident and compiled witness statements. Several witnesses reported seeing a dark colored, low flying helicopter shortly before the time of the accident. Approximate locations of six witnesses were plotted on a sectional aeronautical chart. The number designations noted below correspond to the labels on the plot. The plot is included with the docket material associated with this accident file.

A witness (#1) reportedly located about 12 miles north-northwest of Richland Center, Wisconsin, in an area known as Woodstock, told a sheriff's detective that a dark-colored, "medical type" helicopter flew past his residence toward the southeast between 1915 and 1930. The witness stated that it was flying at or below 200 feet above the hilltops and that it was very loud. The witness reportedly told the detective that the helicopter came through "very, very fast" and was gone.

Two witnesses (#2) located about 11 miles northeast of Richland Center, Wisconsin, in an area known as Pleasant Ridge, reported that a dark blue helicopter flew over their dairy farm about 1930. They estimated it was at an altitude of 50 feet above ground level (agl) based on the height of one of their silos. One of the witnesses noted that they had put an addition onto the silo, which started at the 50-foot level. She stated that as the helicopter flew over their farm, it was "right at" the 50-foot line.

A witness (#3) in the vicinity of Hillpoint, Wisconsin, told a sheriff's detective that a helicopter flew over her residence at "tree top level" between 1930 and 2000. She commented that it was flying "very fast and very low." She noted that it was eastbound at the time and that there did not appear to be any type of mechanical distress.

Two witnesses (#4) located near Loganville, Wisconsin, reported seeing a dark-colored helicopter flying in a southeasterly direction at an altitude of approximately 40 feet agl. They reportedly based this estimate on some 55-foot trees high near the flight path. They stated that the helicopter was flying below the top of these trees. The witness noted that at one point they thought the helicopter was going to hit a rock outcropping, when at the last minute it maneuvered around it.

Another witness (#5) reported that he was at his home near Loganville, Wisconsin, when he heard a "very loud" noise and went outside to observe a large black helicopter flying "very fast." The witness stated that the aircraft was flying close enough to his silos that he was able to see that it was at or below their tops, which were 70 feet tall.

A witness (#6) approximately 3 miles west of the accident site, stated that the helicopter came in "very fast" over a hill to the north of his location. The witness stated that the helicopter was traveling eastbound and came over his home about 20 feet agl. The witness noted that it was blue in color and approximately the size of a medical evacuation helicopter.

A witness to the accident reported that he was docking his boat in Gruber's Grove Bay when a low flying helicopter drew his attention. He stated he thought that the pilot was descending to "buzz" the bay. He noted that he looked away for a moment to dock the boat. When he looked back the helicopter was passing overhead doing a "slow [forward] roll" with debris coming off the aircraft. He reportedly lost sight of the helicopter as it disappeared over some trees. He noted that a "soft explosion" sound was heard and he observed smoke rising over the trees. He stated that when he looked back to the west, he observed power lines "bouncing."

In a follow-up interview, this witness commented that the power lines were between his position and the helicopter. He described the helicopter's flight path as "very direct" and recalled that the aircraft was not "wavering" as it flew toward them. He stated that he did not observe any smoke and that it sounded normal. He noted that it approached at a high rate of speed, comparable to speeds of fixed-wing aircraft.

A second witness in the same boat stated that she first noticed the helicopter when it was "high up" in the distance. She reported that it kept getting lower, coming directly at them. She stated that the helicopter approached traveling in a straight line and that it sounded normal to her. She commented that she did not see it strike the power lines, but after it passed overhead noticed that the wires were "bouncing." She recalled components coming off the aircraft. The helicopter subsequently disappeared behind some trees. She then heard a sound she thought was the impact and saw flames and smoke.

A third witness to the accident sequence stated that she was inside her home when she noticed the helicopter "dip" towards the opposite side of the lake. The noted that she ran outside and saw the helicopter "weave up and down." It dipped low toward the water and then came back up toward the power lines. She stated that she saw the tail separate from the aircraft and the helicopter went over the trees and impacted a residence across the lake from her location.

An employee of the power company reported that electrical service in the vicinity of Gruber's Grove automatically tripped off at 1958:58. A technician was dispatched to the accident site and reported that one of the static wires was sagging and was wrapped around one of the conductor lines in two locations. He noted that the second static line also appeared to be sagging.

A journey log was recovered at the accident site. It was damaged during the post-impact fire but was partially legible. Log entries included flights throughout the southern and western United States. The initial flight of this trip was from Ft. Lauderdale, Florida, to Tallahassee. Florida. According to the pilot's logbook, this flight was conducted on June 30, 2004. Subsequent flights included destinations of New Orleans, Louisiana; El Paso, Texas; Las Vegas, Nevada; San Diego, California; San Francisco, California; South Lake Tahoe, California; Jackson Hole, Wyoming; Salt Lake City, Utah; Seattle, Washington; and Billings, Montana. The last entry in the log was from Huron, South Dakota, to Rochester, Minnesota.

A Federal Aviation Administration (FAA) inspector obtained fueling information for the accident aircraft. The helicopter was fueled at BIL with 70 gallons on August 5th. On August 6th, the day of the accident, the helicopter was fueled at EFC with 89.7 gallons at 1130. The aircraft reportedly departed EFC about 1150. The helicopter was subsequently fueled at HON with 109 gallons about 1500. The aircraft was fueled with 110 gallons at RST about 1834.


The pilot held commercial pilot certificate issued by the FAA with single and multi-engine land airplane and rotorcraft helicopter ratings. His certificate included an instrument rating valid for airplanes and helicopters. He was issued a second-class airman medical certificate on February 5, 2003. The certificate included a limitation that the holder must wear corrective lenses for distant vision and must have lenses for intermediate vision correction available.

The pilot was a citizen of the United Kingdom. He held a private pilot's certificate issued by the United Kingdom Civil Aviation Authority. The document indicated operating privileges for both single and multi-engine land airplanes and for helicopters.

A pilot logbook containing the accident pilot's name was recovered and reviewed. It included entries dated from December 6, 2000 to July 5, 2004. The first page of the log indicated prior flight time of 402.6 hours forwarded to that book. The journey log recovered at the site included additional flights not logged in the pilot's logbook. The pilot's flight times were compiled based on the pilot logbook and journey log entries. He had a logged total flight time of 1,211 hours. Of this total, 534 hours were in helicopters. He had logged 60.7 hours within the previous 30 days, and 152.6 hours within the preceding 90 days. The accident flight was approximately 1.0 hour.

According to the pilot's logbook, his first flight in an EC130 B4 helicopter was on May 26, 2004. Logged flight time in EC130 B4 aircraft was all in the accident aircraft and totaled 146.2 hours. Of this flight time, 85.5 hours were logged as dual instruction received.

The accident pilot completed transition training for the EC130 B4 helicopter provided by the American Eurocopter Training Center. According to records provided by Eurocopter, the training consisted of initial ground school and 3.4 hours flight training. The program was completed on June 8, 2004.

The pilot-rated passenger held a student pilot certificate issued by the FAA on May 11, 2004. He also held a second-class airman medical certificate issued on February 5, 2004. A record of his flight time was not obtained. The pilot-rated passenger was a United States citizen.

The pilot-rated passenger completed the EC130 B4 initial ground school training course provided by the American Eurocopter Training Center on May 20, 2004.


The accident helicopter was a Eurocopter EC130 B4 (serial number 3774) manufactured in 2004. The EC130 B4 is a turbo shaft powered aircraft, with a three-blade main rotor configuration. The tail rotor incorporated a shrouded, Fenestron design. The accident aircraft interior was equipped with 7 seats in a passenger transport layout. An emergency medical services (EMS) interior arrangement was also available in this model helicopter.

Weight and balance data for the accident helicopter indicated that the empty weight was 3,385 pounds. The maximum gross weight limit was 5,351 pounds for normal (internal load) operations.

The helicopter was equipped with a Turbomeca Arriel 2B1 turbo shaft engine (serial number 23085). It is a free turbine configuration, capable of producing 847 shaft horsepower. The engine assembly consisted of axial and centrifugal compressors, an annular combustion chamber, gas generator turbine, power turbine, and exhaust section. The power turbine drives an external gearbox, which in turn supplies power to the rotor system via the transmission shaft.

The helicopter had accumulated approximately 202 hours since new. Records indicated that the aircraft was imported to the United States with 3 hours total time. A standard FAA airworthiness certificate was issued on May 25, 2004.

An annual inspection was completed on June 15, 2004, according to maintenance records. Total aircraft flight time at the time of the inspection was 111.1 hours. Maintenance records indicated that the applicable airworthiness directives had been complied with at the time of the accident.

The engine had accumulated approximately 202 hours total time since new. The most recent inspection was accomplished on June 29, 2004. According to the logbook entry, 15, 25 and 50-hour inspections were completed at that time. The engine had accumulated 111.1 hours at the time of that inspection. The records indicate that the applicable airworthiness directives had been complied with at the time of the accident.

According to records provided by the operator, on July 13, 2004, the pilot reported that the hydraulic system warning light had illuminated and that the hydraulic filter bypass indicator button had tripped. The maintenance logbook entry stated that the left-hand lateral servo, the forward/aft servo, and the hydraulic filter were replaced. No further maintenance logbook entries were located.


The Dane County Regional Airport - Truax Field (MSN) Automated Surface Observing System (ASOS), at 1953, recorded: Winds from 250 degrees at 4 knots; visibility 10 statute miles, clear skies, and temperature and dew point were 21 degrees Celsius and 11 degrees Celsius, respectively. The accident site was located 21 miles west of MSN.

According to United States Naval Observatory data, sunset on the day of the accident was at 2014. Civil twilight ended at 2045.


The main wreckage was located next to a single-family residence in the Gruber's Grove area of Sauk County, Wisconsin. The property was on the shoreline of Lake Wisconsin, north of Prairie du Sac. Coordinates of the main wreckage were determined by a handheld global positioning system receiver. The main wreckage coordinates were 43 degrees 19.548 minutes north latitude, 089 degrees 43.072 minutes west longitude.

A set of power lines extended across Gruber's Grove Bay adjoining Lake Wisconsin. The lines were located approximately 350 feet northwest of the accident site. The set of lines was composed of three transmission wires and two static lines. According to the power company, the tops of the H-frame support poles were about 79 feet agl. The static lines were secured near the top of the poles.

The main wreckage debris covered an area approximately 10 feet by 4 feet and was located adjacent to the north wall of the residence. Main rotor blades were lying against the home. They remained attached to the rotor hub. The main rotor transmission and engine were located in the main debris area. The composite sections of the fuselage structure were reduced to ash by the post-impact fire. The main rotor blades sustained damage consistent with a fire.

The interior and exterior of the residence sustained fire damage. The roof had a hole about 8 feet in diameter at the northwest corner of the home. The room below the hole sustained fire damage.

The perimeter of the yard along the lake shoreline was lined by trees approximately 35 feet high. No tree strikes were observed on any trees between the accident site and the power lines.

Additional debris was recovered from the backyard of the residence. The debris included the aircraft battery, a lower section of left cabin entry door, and small sheet metal pieces consistent in appearance with tail boom and fuselage structure. None of these items was discolored or showed signs of fire damage.

The Fenestron assembly and a section of the tail rotor drive shaft were recovered from the bay. The tail rotor blades and pitch control linkage were found intact. The upper section of the Fenestron rotor duct exhibited scrape/wear marks approximately 14 inches in length. The aft end of the housing exhibited crushing damage consistent with impact. A section on the left side of the upper fairing was separated. The remaining (attached) portion of the fairing exhibited scrape marks. The Fenestron assembly was not discolored and showed no evidence of fire damage.

The tail rotor drive shaft fractured at the point where it entered the Fenestron housing at the aft end of the tail boom. The appearance of the fracture surface was consistent with torsional overload.

The main transmission assembly sustained damage consistent with impact forces and fire. The steel rod ends common to the pitch change links remained secured to the pitch change horns on the main rotor blade hub. The aluminum portions of the links were not present. The pitch change horns remained secured to the main rotor hub.

The Turbomeca Arriel 2B1 turbo shaft engine was torn down under direct supervision of the NTSB. The engine external case was dented at several locations and discolored. The engine modules and individual components were disassembled and examined. The axial compressor inlet was dented. Scrape marks were observed on the inside of the inlet housing opposite the compressor blade disc. The blades exhibited leading edge gouges but were otherwise intact.

The gas generator module external case was dented. The centrifugal compressor disc was intact. Scrape marks were observed on the ends of the blades and on the inside of the housing. All diffuser vanes were present, however, some exhibited trailing edge damage. The gas generator turbine disc was intact. The compressor and turbine discs did not rotate.

The power turbine module was disassembled from the gas generator module. The power turbine blade disc was free to rotate. The power turbine blades were intact. Scrape marks were observed on the forward face of the disc near the blade roots. The radial location of these marks approximately matched similar scrape marks on the vane assembly at aft end of the gas generator module. The outboard leading edges of several blades exhibited were chipped or gouged. The aft bearing was intact and rotated freely.

The reduction gearbox was inspected and disassembled. The power input (upper) and power output (lower) shaft splines were intact. All internal gears were intact and apparently undamaged. All bearings were intact and free to rotate. The gears rotated under hand pressure with some binding.

The engine power shaft and the main rotor gearbox drive shaft were both twisted. The engine power shaft was twisted at a point about mid-length. The transmission shaft was twisted at the forward end, adjacent to the main gearbox attachment flange. The flector group assembly coupling bolts were installed and secure. The free wheel shaft splines from the reduction gearbox were intact and appeared undamaged.

The free wheeling unit was intact and securely attached to the transmission and tail rotor shafts. It could not be rotated under hand pressure. It was discolored consistent with fire damage.

The power transmission line support poles were visually inspected. The inspection revealed that the angle irons supporting the static line on the first and second support poles south of the bay were bent. They were each bent toward the bay in the direction of the accident site. The power company reported that the damage was not present prior to the accident.


Autopsies of the pilot and pilot-rated passenger were conducted at the University of Wisconsin - Madison Medical School on August 8, 2004.

Toxicology samples for both aircraft occupants were submitted to the FAA Civil Aero Medical Institute for testing. The toxicology reports were negative for all substances tested.


The mounting flange common to the Fenestron and the aft end of the tail boom was examined by the NTSB materials laboratory. The component was fractured 360 degrees around the forward side of the flange. A 6.2-inch length of the flange (between the 4:30 and 6:00 o'clock position, looking aft) showed metal smearing with the remaining fracture surface showing features consistent with overstress.

Features in the smeared area were oriented in an outboard-inboard direction and were consistent with contact with another object. The smearing was not consistent with rubbing of the fracture surfaces.

Further analysis of a clean area of the fracture revealed base metal components consistent with 2024 aluminum alloy. Analysis of portions of the smeared area appearing lighter in color revealed elevated levels of zinc as related to the base material.

The electrical power company reported that the static power lines near the accident site were constructed of 3/8-inch diameter, 7-strand galvanized steel.

The directional metal transfer features on the fracture, the high-energy rolled over material with serrated features and the transferred zinc on the fracture are consistent with impact with a galvanized steel static line.

The area of the accident as depicted on the Chicago Sectional Aeronautical Chart was reviewed. The power transmission lines running along the northwest side of Lake Wisconsin were indicated on the chart. Additionally, the chart showed the lines crossing over the Gruber's Grove Bay inlet of the lake adjacent to the accident site.

Regulations related to obstruction marking were reviewed. The transmission lines crossing the bay do not require obstruction markings, according to 14 CFR Part 77, "Objects Affecting Navigable Airspace." FAA Advisory Circular 7460-1, "Obstruction Marking and Lighting," states that any structure exceeding an overall height of 200 feet agl should normally be marked and/or lighted. The power line support structures were about 80 feet agl.


Parties to the investigation were the FAA, American Eurocopter and Turbomeca USA.

The main wreckage was released on September 8, 2004, and was acknowledged by the Sauk County Sheriff's department. The Fenestron-to-tail boom mounting flange was retained for metallurgical examination and subsequently released on December 30, 2004.