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N9158U accident description

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Crash location Unknown
Nearest city Drummond, WI
46.326338°N, 91.296300°W

Tail number N9158U
Accident date 24 Sep 2005
Aircraft type Robinson R44
Additional details: None

NTSB description


On September 24, 2005, about 1105 central daylight time, a Robinson R44, N9158U, operated by Midstate Aviation Inc. (Midstate Helicopters Inc.), received substantial damage on impact with a power line and Hammil Lake, near Drummond, Wisconsin, while providing rides during a Fall festival at Cable, Wisconsin. Visual meteorological conditions were recorded at the time of the accident. The 14 CFR Part 91 revenue sightseeing flight was not operating on a flight plan. The pilot and two passengers were fatally injured. The local flight departed about 1100.

A witness stated that he was walking with his father in a field when he heard the helicopter that was working the Fall festival. He heard the pitch of the helicopter change, the rpm increase, and then heard a muffled crash after which he no longer heard the helicopter rotor. The pitch change lasted for 1-2 seconds. He did not hear any sputtering of the engine. It sounded like it hit water, but he added that he never heard a helicopter crash before. He talked to fishermen at Hammil Lake who said they didn't see anything. He then took their boat and went down the lake where he saw debris and a downed power line. He first saw cushions on the lake surface and then debris protruding from the water surface. He said that the debris was actually one of the helicopter's fuel tanks, which smelled like fuel.

The witness stated that the weather was cloudy, foggy, and misty. There was no ground fog. He stated that when he was on Lake Hammil, it was gray. The clouds were about 1,000 feet above the ground and visibility was good when it wasn't raining; it wasn't raining at the time of the accident. He said that the winds were from the south.


The pilot held a commercial pilot certificate with a rotorcraft-helicopter rating issued December 20, 2004. At the time of issuance, the pilot reported a total airplane flight time of 32.9 hours with 29.1 hours of instruction received and a total rotorcraft flight time of 141.0 hours with 84.7 hours of instruction received. The pilot was issued a certified flight instructor certificate with a rotorcraft-helicopter rating on April 6, 2005, at a total airplane flight that remained unchanged and a total rotorcraft flight time of 214.1 hours, of which 145.8 hours was instruction received. The pilot received a second class airman medical certificate on April 25, 2005, with a total reported aircraft flight time of 260 hours.

Pilot logbooks were requested from the operator and pilot's wife both of whom stated that they did not know where the logbooks were. No pilot logbooks were received by the National Transportation Safety Board (NTSB) or FAA after these requests.


The 1999 Robinson R44 helicopter, serial number 0604, powered by a Lycoming IO-540-AE1A5, serial number L-25403-40A, engine was registered to a corporation, Midstate Aviation Inc., on July 19, 2001. The helicopter and engine were last inspected during a 100-hour inspection on July 20, 2005, at an aircraft and engine total time of 1,711 hours and a Hobbs time of 1,711 hours.


First responders reported the helicopter was resting in Hammil Lake at a depth of about 20 feet near a downed power line. The wreckage possessed a twisted strand cable that was wrapped around the main rotor mast and was embedded in the main rotor blades, which exhibited fracture and separation. The tail boom was separated from the fuselage and the tail rotor blades did not display damage.

Both landing gear cross tubes were separated from the fuselage. The right skid tube was fractured about midpoint near the forward cross tube. The left skid tube was fractured in three locations near the forward and aft cross tubes. The right forward cross tube, near and outboard of the fuselage attachment, was missing a portion of its fairing exposing the underlying cross tube, which exhibited gouging. The aft cross tube was fractured near the left fuselage mount.

The main rotor was rotated by hand and the pulley shaft was rotated through 360 degrees. Fractures in the main rotor transmission housing exhibited granular fracture surfaces. The "Teletemp" temperature recorder strip stripe was white on 220 degrees, 230 degrees, 240 degrees, 250 degrees, 260 degrees and 270 degrees. The four main transmission pulley drive belts were intact.

Examination of the tail rotor gearbox revealed the presence of a fluid consistent with lubricant within the gear box. The tail rotor blades rotated when the input drive to the gear was rotated by hand. The tail rotor gear box chip detector was removed and noted not to contain debris. The "Teletemp" temperature recorder strip , model 110-2, had a brown discoloration on strip portions annotated 140 degrees, 150 degrees, and 160 degrees. The strip portions annotated 170 degrees, 180 degrees, and 190 degrees were white in color.

The tail rotor drive shaft was twisted at a location about 3 feet from its forward end. Fractures along the tail rotor drive shaft exhibited a 45-degree fracture surface.

The engine top spark plugs were removed and the engine was rotated by hand and then with the electrically driven engine starter. During the engine rotation, air was expelled and drawn into each cylinder and engine continuity to the accessories was noted. During the engine rotation, fluid consistent with water, was expelled from the oil filter output. A spark from each magneto lead was obtained when the magneto drive shafts were rotated.

The ignition key switch was in the BOTH position. The Hobbs meter indicated 1,789.9 hours. The cyclic friction control was in the full counterclockwise position. The control stick was moved by hand and the main rotor blades rotated about their lateral axis. Flight control continuity was confirmed from the cockpit controls to their respective control surfaces.


An autopsy of the pilot was conducted by the Minnesota Regional Coroner's Office on September 26, 2005.

The FAA Forensic Toxicology Fatal Accident Report was negative for all substances tested.


According to first responders, the pilot and rear seat passenger were located within the helicopter and the left front seat passenger was located outside of the helicopter.

The on-scene inspection of the restraint system noted fractures in the seat belt buckle release assemblies. All of the release assemblies, webbings, and reels were removed and sent to the NTSB Materials Laboratory Division for examination.


Letters dated August 14, 2005, and September 9, 2005 to the FAA's Minneapolis Flight Standards District Office (FSDO) and Robinson Helicopter Company regarding Midstate Aviation Inc, were received from an individual who witnessed a Robinson R44 at 500 feet AGL "coming out of an ag-turn" near Princeton, Minnesota, while providing rides. This witness continued to watch the helicopter and observed maneuvers that included pull-ups and push-overs. The witness stated that he has logged over 1,200 hours in the Robinson R44 helicopter and has attended the Robinson Helicopter Safety Course for flight instructors. The witness stated that the helicopter was being operated in a manner contrary to all safety guidelines outlined at the Safety Course and Special Federal Aviation Regulation 73.1.

The owner of Midstate Aviation Inc. stated that they have been in business providing air rides for 4 1/2 - 5 years and it was their only helicopter. This was their first time flying in the Cable, Wisconsin, area, which began on September 23, 2005. He stated that during the rides at the Cable, Wisconsin, festival, the helicopter would approach and land from the south and takeoff toward the north due to the wind. He stated the he would "hook up" the passenger seatbelts for the helicopter rides and no safety briefing that would included emergency exits and operation of the restraint system was given. The helicopter would not be shutdown when passengers were loaded or unloaded. He stated that there was no standard route for helicopter rides and that it was a "customer service" with most people wanting to fly over their houses. He stated the he has received complaints regarding the "wild ride" they would offer which was discussed with the FAA's Minneapolis Flight Standards District Office. They no longer offer "wild" rides but only "normal" rides.

A passenger who received a helicopter ride in N9158U on the morning of September 24, 2005, at 1000-1015 stated that there was no cordoned area around the helicopter to delineate a safe area. The helicopter was idling at the time when he got into the front passenger seat. The pilot was out of the helicopter while securing the seatbelts on the passenger and his grandson. There was no passenger safety briefing given by the pilot. He did not notice anything "unusual" about the pilot. The pilot asked him if he had a particular destination and did not ask him if he wanted a "wild" ride. During their flight, the helicopter circled over a wooded area belonging to the passenger's house, then flew over the middle of Lake Owen, and then returned to the town where they circled before landing. The lowest altitude during the flight was over the passenger's house where they were about 100-250 feet above ground level. Over Lake Owen, they were "considerably" higher, estimated to be 3-4 times higher. The passenger stated that the sky conditions included an overcast layer that was "well above them." There was no mist when they departed on their flight.

Federal Aviation Regulation 91.107 Use of Safety Belts, Shoulder Harnesses, and Child Restraint Systems, states in part: (1) No pilot may takeoff a U.S.-registered civil aircraft unless the pilot in command of that aircraft ensures that each person on board is briefed on how to fasted and unfasten that person's safety belt and, if installed, shoulder harness.

The Rotorcraft Flying Handbook, FAA-H-8083-21, states in part, Safety In and Around Helicopters: "People have been injured, some fatally, in helicopter accidents that would not have occurred had they been informed of the proper method of boarding or deplaning. A properly briefed passenger should never be endangered by a spinning rotor. The simplest method of avoiding accident of this sort is to stop the rotors before passengers are board or allowed to depart. Because this action is not always practicable, and to realize the vast and unique capabilities of the helicopter, it is often necessary to take on passengers or to deplane them while the engine and rotors are turning. To avoid accident, it is essential that all persons associated with helicopter operations, including passengers, be made aware of all possible hazards and instructed as to how they can be avoided." The Handbook also states, "Since few helicopters carry cabin attendants, you, as the pilot, will have to conduct the pre-takeoff and prelanding briefings. The type of operation dictates what sort of briefing is necessary."

The NTSB Materials Laboratory Report of the restraint system buckle release assemblies states that the stainless steel loop on the left front belt was fractured, separating the buckle from the attachment to the fuselage. Examination of the other three buckles found cracking at similar locations in the straps. The left front seat strap was transversely fractured through the two hollow rivets connecting it to the release assembly. The upper fracture was bent away from the lower fracture allowing the buckle to separate from the strap. The rivets were still tight in the release assembly. The tongue portion of the buckle assembly was bent away from the occupant about 15-20 degrees. Close examination of the strap revealed multiple fractures and cracks at each rivet hole. Microscopic inspections including scanning electron microscope viewing uncovered heavy metal rubbing damage to the fracture faces that obliterated most of the fine fracture details. Sufficient details remained to establish that multiple fatigue cracks initiated near both of the rivet holes with propagation away from each hole. The fracture between the fatigue fracture and strap edges were consistent with final overstress separation. Transversely, the fatigue regions measured approximately 1.3 inches with 0.25 and 0.3 inch long overstress fractures at each edge. Energy dispersive x-ray spectral composition was consistent with a 300 series stainless steel containing iron, chromium and nickel. Measurements found the strap material to be nominally 0.020 inch thick. The right front seat strap contained multiple cracks between and adjacent to the two hollow rivets. The pattern of multiple cracks was very similar to that in the left front strap. The cracked region measures about 1.45 inches across the strap with a 0.2 inch ligament of intact material at each edge of the strap. The intact ligaments were abrasively cut to allow viewing of the crack faces. Similar to the left front seat belt, the fracture faces were damaged by mutual rubbing of the faces. Undamaged features indicated multiple fatigue regions with initiation near the holes. Eight different fatigue regions were noted. The left rear and right rear seats had crack patterns similar to both front seat positions. The cracks were not opened for further examination.

A Special Airworthiness Information Bulletin (SAIB) SW-06-19, dated December 28, 2005, was issued by the FAA's Aircraft Certification Service for Robinson Helicopter Company R44 and R44 II model helicopter seat belt buckle assembly part number C628-4. The SAIB recommended, in part, to "visually inspect seat belt buckle assembly stainless steel straps, particularly in the vicinity of rivets. If you find cracks, replace the seat belt buckle assembly before flight.

A Robinson Helicopter Company Service Bulletin SB-56, dated March 29, 2006, was issued for C628-4 revision M or prior seat belt buckle assemblies (originally installed in R44's thru SN 1576 and R44 IIs thru SN 11107)

Federal Aviation Regulation 91.119, Minimum Safe Altitudes: General, states, in part: Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:

(a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface. (b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft. (c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those case, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure. (d) Helicopters. Helicopters may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section if the operation is conducted without hazard to persons or property on the surface. In addition, each person operating a helicopter shall comply with any routes or altitudes specifically prescribed for helicopters by the Administrator.


Parties to the investigation were the FAA, Textron Lycoming, and Robinson Helicopter Company.

(c) 2009-2018 Lee C. Baker / Crosswind Software, LLC. For informational purposes only.