MANILA, AR, USA
N482SA
Southwest Florida Aviation SW204
The pilot was applying pesticide to a cotton field when the outboard 9 feet of one main rotor blade separated in flight, resulting in the main rotor system separating from the main transmission mast. The in-flight separation of the main rotor blade was due to fatigue cracks emanating from a puncture through the lower surface of the blade in the leading edge area. The shape of the puncture, the crater mark above the puncture, and surrounding areas containing heavy deposits of lead residue indicated a bullet had entered the blade. The puncture had been repaired; however, manufacturer's specifications stated that this type damage is nonrepairable and the blade should be scrapped. In July 1995, the rotor blade was modified. During the modification process, the blade was inspected for damage. In April 1997, an AD requiring inspection of the blade was complied with.
HISTORY OF FLIGHT On August 27, 1997, approximately 1010 central daylight time, a SW Florida Aviation SW204 helicopter, N482SA, was destroyed following an in-flight separation of a main rotor blade while maneuvering, near Manila, Arkansas. The helicopter was registered to and operated by the pilot, DBA Buffalo Island Flying Service, as a Title 14 CFR Part 137 aerial application flight. Visual meteorological conditions prevailed, and a flight plan was not filed for the local flight. The commercial pilot, sole occupant of the helicopter, was fatally injured. The flight originated from the pilot's private airstrip near Manila, Arkansas, about 5 minutes prior to the accident. The pilot was applying the pesticide Karate to a nearby cotton field. There were no reported eyewitnesses to the helicopter crash; however, one witness reported hearing the sound of the engine RPM rapidly increasing followed by the sudden termination of the engine sound. Subsequently, the witness heard the sound of the helicopter impacting the ground. PERSONNEL INFORMATION The non-instrument rated commercial pilot added a helicopter rating to his commercial certificate on November 25, 1979. According to the pilot's flight logbook, he had accumulated a total of 15,457.7 flight hours in all aircraft, of which 1,775.5 hours were in helicopters, with 85.3 hours in the Southwest Florida Aviation SW204 helicopter (converted military Bell UH-1B). The pilot's last biennial flight review (BFR) was completed in a Maule airplane on January 29, 1997. AIRCRAFT INFORMATION According to Bell Helicopter, the original manufacturer of the helicopter, the aircraft was delivered to the United States Army on January 20, 1964, as a UH-1B helicopter with a serial number of 63-8534. FAA records indicate that on February 9, 1993, the accident aircraft was assigned the registration number of N482SA after being imported back into the United States. On March 8, 1993, the aircraft was registered to Southwest Florida Aviation, Inc., of Punta Gorda, Florida. On June 1, 1995, Southwest Florida Aviation, Inc., completed a conversion of the UH-1B to a Southwest Florida Aviation SW204 helicopter under the type certificate No. H6SO. The Southwest Florida Aviation SW204 helicopter, serial number 756, was issued a Special Airworthiness Certificate on June 22, 1995, in the restricted category. During a personal interview conducted by the NTSB IIC, a representative from Hillcrest Aircraft Company, Inc., of Lewiston, Idaho, reported that they acquired the helicopter from Southwest Florida Aviation in July 1996. The helicopter was not in flyable condition. According to FAA records, on March 4, 1997, the Southwest Florida Aviation SW204 helicopter, serial number 756, was registered to the Hillcrest Aircraft Company, Inc., as a UH-1B helicopter, serial number 63-8534. The representative from Hillcrest Aircraft Company, Inc., further reported that they sold the helicopter "as is" to the pilot, Sidney R. Atkison, about February 1997. According to FAA records, on March 25, 1997, the aircraft was registered to the pilot, Sidney R. Atkison, dba Buffalo Island Flying Service. The pilot contracted Tamarack Helicopters, Inc., of Stevensville, Montana, to put the aircraft into an airworthy condition. On April 20, 1997, Tamarack completed the re-assembly of the helicopter from its storage and shipping condition. According to the aircraft's maintenance records, the helicopter was certified in airworthy condition on April 20, 1997, with 4,972.9 hours total airframe time. Airworthiness directive (AD) 75-26-05, inspection of main rotor blades, was also complied with on April 20, 1997. See the enclosed copy of AD 75-26-05 and the related Bell Helicopter service bulletin for inspection requirements. According to the pilot's flight logbook, on April 17, 1997, the pilot received a check ride in the helicopter at Hamilton, Montana. His pilot flight logbook also showed that he ferried the aircraft from Hamilton, Montana, to Manila, Arkansas, on April 18, 1997. According to a packing slip from Tamarack Helicopters, the helicopter's maintenance logbooks were shipped to the pilot on May 16, 1997. WRECKAGE IMPACT INFORMATION The aircraft wreckage was located in a cotton field approximately 2 miles north of Manila, Arkansas, at latitude 35 degrees 56.6 minutes north and longitude 90 degrees 11.3 minutes west. Examination of the accident site revealed that the helicopter came to rest on its top right side. Its final resting heading was measured at 320 degrees magnetic. The cabin roof was crushed inward and the main transmission was only attached to the fuselage by the lift link. The tail boom was partially separated from the fuselage, and the tail rotor was partially attached to the vertical stabilizer by its pitch change chain/cable. The main rotor system was separated from the main transmission mast, and the main rotor was found approximately 110 feet southeast of the main wreckage. The main rotor hub and blade assembly was found separated from the mast near the bottom of the hub, and the fracture surface displayed evidence of shear overload. The outboard 5 feet of one main rotor blade, serial number RB0154, was separated and found near the hub and blade assembly. The other main rotor blade, serial number RB0156, had the outboard 9 feet separated, and it was not located in the area of the wreckage. This portion of the rotor blade was located on or about November 10, 1997, across a creek to the northwest of the main wreckage. The fractured fragments of main rotor blade RB0156 were sent to the NTSB Materials Laboratory in Washington D.C., for examination. The engine was found in position on the engine deck; however, its mounts were fractured. Complete engine continuity could not be establish at the accident site, therefore the engine was sent to the engine manufacturer's facility in Phoenix, Arizona, for further examination and testing. MEDICAL AND PATHOLOGICAL INFORMATION The autopsy was performed by pathologist Steven A. Erickson, M.D., at the Arkansas State Crime Laboratory, in Little Rock, Arkansas. Toxicological findings were negative. TESTS AND RESEARCH A teardown inspection of the Allied Signal Lycoming T53-L-11D turboshaft engine, serial number LE-13147, was conducted at the AlliedSignal Product Safety and Integrity Investigation Laboratory on October 28, 1997, under the supervision of the NTSB investigator-in-charge. According to the manufacturer's teardown report, "there was evidence of rotation and operation at the time of impact with the ground." Additionally, the report states that "no pre-existing conditions were found that would have interfered with normal operation of the engine." See the enclosed AlliedSignal report for details of the examination. The fractured fragments of main rotor blade RB0156 were examined at the NTSB Materials Laboratory in Washington D.C., on November 13 and 14, 1997. Examination of the fragments revealed a chordwise fracture that intersected a puncture in the lower surface of the blade. The puncture was located approximately 5 inches aft of the leading edge and 108.5 inches from the outboard end of the blade. The puncture shape was circular with an approximate diameter measuring between 0.27 and 0.31 inch. The puncture penetrated the three bottom metal layers of the blade: the abrasion strip, doubler, and lower portion of the box beam (spar). The upper inside surface of the box beam in a position located almost directly above the central axis of the puncture displayed an impact crater. The surface of the crater, the area surrounding the crater, and the forward upper corner of the aft inboard wall of the box beam were covered with a gray-white deposit. Energy dispersive X-ray spectrographic (EDS) spectra of these gray-white deposits contained large peaks of the element lead. The puncture, crater, and lead deposits, appeared consistent with a lead tip bullet impacting with the blade from the underside. Scanning electron microscope (SEM) examination of the chordwise fracture revealed fatigue cracks propagating from diametrically opposite sides of the puncture. In the abrasion strip, fatigue cracking emanated from the puncture and extended forward, then up to the upper surface where the nose block mates with the upper doubler, which is nearly through 70 percent of the abrasion strip structure. Fatigue cracking in the lower skin emanated from the puncture and extended aft to the trailing edge. Fatigue cracking in the lower doubler emanated from the puncture and propagated both forward and aft through nearly 80 percent of the lower doubler cross section. This doubler contained a secondary fatigue origin slightly aft of the puncture. In the box beam, fatigue cracking emanated from the puncture and propagated forward and aft, then up to the corners. Fatigue features were found through approximately 60 percent of the box fracture cross section. Another fatigue crack emanated from the lower corner of the nose block doubler and extended through approximately 40 percent of the nose block wall fractured cross section. The fracture areas outside the fatigue regions contained features typical of overstress separations. Stereo microscope examination of the chordwise fracture showed the puncture remnant was filled from the outside to the inside surface, respectively with nonmetallic tan filler material, fiberglass, gray filler material, and metallic foil. The metal foil was identified by EDS analysis as aluminum. The outside surface in the filled area was smooth and level with the surrounding blade surface. The exterior surface of this fragment and those of the other fragments contained a uniform black coat of paint, with no visible signs of local application of paint. Examination of the fracture surface disclosed that the lower surface of the blade contained multiple layers of paint in the vicinity of the puncture that were colored black, gray, yellow, black, white, and yellow again, from the outside to the inside, respectively. See the enclosed Metallurgist's Factual Report for further details. Army technical manual TM 55-1520-219-23 for UH-1B helicopters states that "main rotor blades damaged to following extent, shall be condemned locally, rather than returned to an overhaul facility. Any penetration through spar, trailing edge strip, doublers, grip plates, or drag plates." Army technical manual TM 55-1520-210-20 for UH-1H helicopters states "non-repairable damage: Any hole through the leading edge spar. Any hole through the skin that is closer than 6.50 inches to the leading edge." Bell Helicopter manual BHT-204B-M&O states "ANY WEAR OR DAMAGE IN EXCESS OF THAT ALLOWED IN THIS SECTION IS CAUSE FOR BLADE REPLACEMENT. Any penetration through spar, trailing edge strip, doublers, grip plates, or drag plates." See enclosed excerpts of these manuals. The main rotor blade was originally manufactured by Bell Helicopter Textron as an UH-1H main rotor blade with a serial number of A8115, and it was delivered to the Red River Army Depot as a spare on January 3, 1987. According to Rotor Blades Modification, Inc., of Punta Gorda, Florida, they purchased the rotor blade from Southwest Aero Parts of San Antonio, Texas. During July 1995, the rotor blade was modified in accordance with STC SH2621SO to meet -15 main rotor blade specifications (UH-1B). After modification completion, Rotor Blades Modification, Inc., assigned it the serial number RB-0156 with a Blade Life Remaining of 663.6 hours. On July 26, 1995, the rotor blade was sold to Southwest Florida Aviation. According to N482SA's maintenance records, the rotor blade was installed on the accident aircraft, in July 1995, with a Blade Life Remaining of 663.6 hours, at a helicopter total time of 4,972.9 hours. The other main rotor blade was originally manufactured by Bell Helicopter Textron as an UH-1H main rotor blade with a serial number of A8734, and it was delivered to the Red River Army Depot as a spare on July 30, 1987. According to Rotor Blades Modification, Inc., of Punta Gorda, Florida, they purchased the rotor blade from Aero Honduras of San Salvador, El Salvador. During July 1995, the rotor blade was modified in accordance with STC SH2621SO to meet -15 main rotor blade specifications (UH-1B). After modification completion, Rotor Blades Modification, Inc., assigned it the serial number RB-0154 with a Blade Life Remaining of 252.2 hours. On October 3, 1995, the rotor blade was sold to Southwest Florida Aviation. According to N482SA's maintenance records, the rotor blade was installed on the accident aircraft, in July 1995, with a Blade Life Remaining of 252.2 hours, at a helicopter total time of 4,972.9 hours. During a personal interview conducted by the NTSB IIC, a representative from Rotor Blades Modification, Inc., reported that the company modifies Bell 205 and UH-1H main rotor blades to UH-1B blade specifications. Rotor Blades Modification, Inc., instruction manual No. RB-8726 Procedures And Policies For Modification Of Rotor Blades is used for modifying the rotor blades. Army technical manual TM 55-1520-219-20 and Army Depot Maintenance Work Requirements manual DMWR 55-1560-198 are pertinent to this modification. Each blade is visually inspected for damage. Minor repairs are made to the blade as necessary, and the blade is painted. See the enclosed Rotor Blades Modification, Inc., instruction manual No. RB-8726 Procedures And Policies For Modification Of Rotor Blades for modification procedures and excerpts of DMWR 55-1560-198 for visual inspection and painting procedures. ADDITIONAL DATA The wreckage of the helicopter was released to the owner's representative.
Fatigue failure of the main rotor blade resulting in the in-flight separation of the main rotor system due to the use of an unairworthy blade, and failure of the maintenance personnel who modified the rotor blade and the mechanic who complied with the Airworthiness Directive to locate the unapproved repair. A factor was the unapproved repair of the main rotor blade.
Source: NTSB Aviation Accident Database
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