DEWITT, MI, USA
N8171U
Hiller FH-1100
A Hiller FH-1100 was destroyed on impact with terrain following the separation of a tail rotor blade in cruise flight. The tail rotor blade 'B' was separated 1/4 span from its root and was discovered 700 feet south of the main wreckage. Blade 'A' was found 850 feet south of the main wreckage. The tail rotor blades were overhauled and later removed for blade delamination on July 14, 1986. The inside surfaces of the blade 'A's' skin showed longitudinal streak patterns of debris. The skin trailing edge closure bond contained an adhesive that was bright purple in color. During 1967-1982 tail rotor blades were bonded with FM1000; a cream or off white colored adhesive. Since 1982, FM1000 bonded the skin and doubler and FM73, which is orange brown in color, between the root fitting and doubler. The rivet holes in the skin were worn on the skin surfaces under the upset heads of the rivets. No wear was visible under the manufactured heads. The rivet holes were not round and appeared to have two overlapping diameters consistent with double drilling. The Hiller FH1100 Overhaul Manual Tail Rotor Assembly, Repair - Tail Rotor Blade Assembly, states, '...Replacement of skin, doubler or rib ... is not permitted.' The Hiller FH1100 Inspection Guide described the inspection of the tail rotor blades during preflight, 100-hour inspection and 300-hour inspection.
HISTORY OF FLIGHT On August 14, 1998, at 1620 eastern daylight time, a Hiller FH-1100, N8171U, operated by Horizon Helicopters Incorporated (Horizon), was destroyed on impact with terrain, in an agricultural field, following the in-flight separation of a tail rotor blade near Dewitt, Michigan. The 14 CFR Part 91 positioning flight was not operating on a flight plan. Visual meteorological conditions prevailed at the time of the accident. The pilot sustained fatal injuries. The flight originated from Horizon's private heliport near Grand Ledge, Michigan, at 1607, and was en route to the Saint Johns Mint Festival, Saint Johns, Michigan. A witness, north of the impact area, stated that he was outside his residence when he heard a loud explosion. When he looked up, he saw the helicopter with pieces flying from it and then crash. He then went inside and called the police. A second witness reported that he was at his residence located southwest of the impact area when he saw the helicopter fly over. He stated that the helicopter was traveling in a northeasterly direction. He heard what he thought sounded something like a gunshot sound and then noticed that the helicopter was going down. A third witness, who resides in an area located south of the impact area, stated that he was inside his residence looking through his sliding glass doors when he noticed the helicopter going down. During a second glance, the witness saw that the main rotor was separated from the rest of the helicopter. Additionally, the witness stated that he did not hear anything nor was he aware that the helicopter had crashed. The operator stated that the pilot/mechanic had performed an annual inspection prior to the flight, but the inspection was not entered into the aircraft maintenance records. OTHER DAMAGE Fuel spillage was reported and soy bean crop damage was present near the aircraft wreckage. PERSONNEL INFORMATION The pilot was 41 years old and the holder of a commercial pilot certificate with airplane single-engine land, airplane multiengine land, instrument airplane and rotorcraft-helicopter ratings. He also held an aircraft mechanics certificate with airframe and power plant ratings. A second class medical was issued to the pilot on September 26, 1997, with no restrictions. A review of the pilot's logbooks revealed that he had accumulated a total airplane flight time of 2,571 hours as of March 16, 1998. The pilot's helicopter logbook showed a total helicopter time of 1,755 hours, of which 86 hours were in turbine helicopters. AIRCRAFT INFORMATION The 1962 Fairchild Hiller 1100, serial number 254, N8171U, was registered to Horizon Helicopters Incorporated and had an estimated total airframe time of 3,821 hours. Serial number 83 was scratched out on the aircraft's data plate and was replaced with serial number 254. On October 29, 1984, United States registration was removed and Canadian registration applied. The aircraft received an airworthiness certificate by the Federal Aviation Administration (FAA) on June 23, 1989. The last annual inspection, logged into the maintenance records, was completed on February 1, 1997, with a total airframe time of 3,687 hours. The engine, Allison 250-C18B, serial number CAE 800802B, is a turbine with an axial centrifugal compressor, a 2-stage gas producer and a 2-stage power turbine with a single combustion chamber rated at 270 maximum continuous shaft horsepower at 6000 rpm. The last engine inspection, logged into the maintenance records, was completed on February 1, 1997, with a total engine time of 3,385 hours. The tail rotor blades, serial numbers 2592 and 2022, had an estimated total time of 1,725 hours and a time since overhaul of 298 hours. Logbook records indicate that the tail rotor blades were repaired and inspected on October 16, 1981 at a time of 1,427 hours. A time of 0 hours since new was also entered into this entry. A logbook entry on May 17, 1985 shows that the tail rotor blades were then installed at a time since new of 1,427 hours and a time of 0 hours since overhaul. On July 14, 1986 the tail rotor blades were removed for "blade delamination" at a time since overhaul of 137 hours. WRECKAGE AND IMPACT INFORMATION The main wreckage was located at latitude 042 52.852' N and longitude 084 38.669' W in an inverted attitude lying on its left side with the attached cabin area, engine, main rotor transmission and tailboom. The wreckage heading was on a magnetic heading of 032 degrees. Within the 20 foot by 10 foot main wreckage area, pieces of the canopy glass and the battery were found forward of the fuselage. The 62.5 gallon fuel tank was found ruptured, and there was an odor similar to that of jet fuel present at the site. The main rotor blades were found on a heading of 230 degrees at approximately 156 feet, in a wooded area, from the main wreckage. The tail rotor gear assembly was discovered to be resting in the wooded area on a heading of 290 degrees and 156 feet without its respective tail rotor blades. The tail rotor blades were discovered to be lying south of the main wreckage in the soy bean field. Blade "B" was separated 1/4 span from the blade root fitting and found 700 feet south of the main wreckage. Blade "A" was found 850 feet bearing south of the main wreckage and separated from the root of the tail rotor assembly. Examination of the engine revealed the engine to rotate, the igniter was free of external debris, the chip detector was free of metallic contaminants and there was no penetration of the compressor and turbine casings. A fractured section of the main rotor shaft was found buried in loose soil relative to the surrounding soil. The bottom side of one of two blades from the main rotor system had three slash marks at three feet from the tip orientated at approximately a 20 degree angle relative to the blades longitudinal axis. The main rotor shaft and both pitch change links exhibited overload fractures. The tail rotor torque tube and rotor mounts exhibited torsional fractures. The transmission and gearbox were intact and were rotated. Flight control continuity was established and the mixer plate was intact. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was conducted by Clinton County, Michigan on August 15, 1998, at 0800. Toxicological tests were negative for all substances tested. TESTS AND RESEARCH The NTSB's Materials Laboratory Examination of blade "A" revealed that the blade skin assembly had separated from the root fitting along the bond line. Also, six of the seven fitting to skin rivets had fractured on both sides of the fitting. The seventh rivet fractured only on the manufactured head side, and the upset head side remained with the fitting. A small piece was fractured from the skin at the location corresponding to the seventh rivet. The adhesive material on the faces of the root fitting of the blades had a shiny orange brown color with darker areas of debris toward the leading edge side of the fitting. An open mesh fabric was embedded into the adhesive material over most of the fitting surfaces. The adhesive was missing from the fitting in several small localized areas particularly on the leading edge horn of the fitting. Bond line thickness was measured with the use of a video based optical measurement system on the face of the root fitting. The bond thickness was found to vary from 0.0004 inches to 0.0146 inches over the surface with the thicker areas located near the leading edge of both sides. The inside surfaces of the skin showed longitudinal streak patterns of debris. The steaks were most apparent along a band projecting outboard from the fitting clearance cutout in the skin. The streaks could be smeared and felt greasy. The skin trailing edge closure bond was opened and found to contain an adhesive that was bright purple in color. Blade "B" was examined and found to contain, on the fitting to doubler, adhesive similar in color, appearance and texture of that of blade "A" for the this joint. The trailing edge closure joint was also similar in color to the blade "A" joint. The doubler to skin joint on blade "B" was bonded with a purple adhesive like the trailing edge joint but was not similar to the same joint of blade "A". During 1967-1982, tail rotor blades were bonded with FM1000 which has a cream or off white color when cured. Since 1982, tail rotor blades have been bonded with FM1000 between the skin and doubler and FM73 between the root fitting and doubler. FM73 has a orange brown color when cured. Magnified examination of the rivet fracture surfaces on blade "A" revealed that all were consistent with shearing overstress. Examination of the rivet holes in the skin found wear on the skin surfaces under the upset heads of the rivets. No wear was visible under the manufactured heads. The rivet holes were not round and appeared to have two overlapping diameters consistent with double drilling. Energy dispersive x-ray analysis of one rivet from the root fitting of each blade found them to have the same elemental make-up that was consistent with a 2000 series aluminum alloy. The skin and doubler on blade "A" were fractured through the rivet hole corresponding to the one intact rivet head remaining on the root fitting. Examination of the fracture surfaces found fatigue features emanating from both sides of the hole. The fatigue fracture emanated from opposite sides of the rivet hole and extended in a chordwise direction in both the skin and doubler. The inner diameter of the rivet hole exhibited wearing and deformation. Another crack was found on the opposite skin at the same rivet hole. The 0.1-inch long crack was only in the skin and not in the doubler. Magnified examination of the fracture found characteristics of fatigue propagation. ADDITIONAL INFORMATION The Hiller FH1100 Overhaul Manual Tail Rotor Assembly, Repair - Tail Rotor Blade Assembly, states, "...Replacement of skin, doubler or rib (1,2, or 3, figure 2-3) is not permitted." The Hiller FH1100 Inspection Guide states the items that are to be performed in the following inspections: No. 1 Check - Preflight, "...17A. Tail rotor blades for missing rivets, condition, and security. ..." No. 2 Check - 100 Hour, "...Rotor blades for bonded joint voids or separation, nicks, scratches, cracks, dents, gouges and corrosion. ..." No. 3 Check - 300 Hour, Tail Rotor Assembly, "...c. Blade tips for excessive erosion; separation of blade bonded joints between skin and internal leading edge doubler (visible at tip and root ends of skin), between skin and tip rib, and between skin and root casting. ..." The Federal Aviation Administration was a party to the investigation. Upon completion of the on-scene field investigation, the wreckage was released to the registered owner on August 15, 1998.
The rotor failure/malfunction due to debonding of the tail rotor blade. Also causal was the inadequate maintenance inspection of the aircraft by the company and the improper maintenance procedure by other maintenance personnel.
Source: NTSB Aviation Accident Database
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