FORT MYERS, FL, USA
N72LC
Hughes OH-6A
According to witnesses, the Lee County Sheriff's Office (LCSO) helicopter flew over the landing area and was on downwind when it suddenly turned to the right, and descend at a high rate of speed, in a nose low attitude, and impact a building. Postcrash examination revealed that the lateral control rod end fitting had separated from the control rod, and the fitting's bearing did not move freely, when compared to a normal rod end bearing. In addition, the rivet that normally passes through the lateral control rod and rod end fitting was missing. Dark and white deposits were found in the threaded region of the rod and rod end fitting, and laboratory analysis of those deposits revealed that the substances were aluminum oxides. Maintenance records show that the control rod had been inspected and modified by Heli-Tech, when the helicopter was first acquired, and had been delivered to the LCSO at about 3546 total flight hours. Following receipt of the helicopter from Heli-Tech, the operator's maintenance log did not indicate any specific maintenance entries related to the control rods. At the time of the accident the helicopter had accumulated 4419.4 flight hours.
HISTORY OF FLIGHT On December 20, 1999, about 0800 eastern standard time, a Hughes OH-6A helicopter, N72LC, registered to and operated by the Lee County Sheriff's Office (LCSO), as a Title 14 CFR Part 91 public-use flight, crashed into the roof of a building. Visual meteorological conditions prevailed, and no flight plan was filed. The helicopter incurred substantial damage, and the commercial-rated pilot, the sole occupant, received serious injuries. The flight originated from Page Field, the same day, about 0745. Witnesses indicated that the helicopter had initially flown over the helicopter-landing pad, and was on the downwind leg, returning for a landing, when they observed the helicopter suddenly turn to the right, and descend at a high rate, in an extreme nose low attitude, impacting the flat roof of a building. One witness also stated that he heard a pop or snapping sound just before the helicopter turned and descended. Another witness, an EMS helicopter pilot, stated that he was in flight, at an altitude of about 450 feet, on a heading of 355 degrees, and was monitoring the Fort Myers Tower frequency when he heard a radio transmission from the pilot of the accident helicopter. The EMS pilot said that the sheriff's helicopter was about a mile north of his location, along his intended flight path, and he heard the pilot of the sheriff's helicopter say that he would be landing at the sheriff's office. The EMS pilot further stated that he saw the sheriff's helicopter below his altitude and on an apparent normal approach to the LCSO helipad. The EMS pilot said that the sheriff's helicopter was on a heading of about 060 degrees, and he watched as the sheriff's helicopter flew past the helipad on about the same heading, and an altitude of about 80 to 100 feet above ground level. The EMS pilot estimated the LCSO helicopter speed to be about 35 to 50 knots, and said that after traveling about 300 to 400 feet, it turned hard right, and descended, impacting the roof of a building, in a nose down attitude. PERSONNEL INFORMATION Records obtained from the FAA Airman's Certification Branch reveal that the pilot holds a commercial pilot certificate with helicopter, airplane multiengine land and instrument airplane ratings. The pilot also possesses a private pilot certificate with an airplane single engine land rating. Logbook pages provided by the pilot and his attorney showed that the pilot had about 9,200 total flight hours, and about 4,000 hours in the OH-6. AIRCRAFT INFORMATION The helicopter, a Hughes OH-6A, serial number 1144A (68-17184), was acquired from the U.S. Army by the LCSO on January 3, 1996. After acquisition by the LCSO, the aircraft was shipped to Heli-Tech, located in Panama City, Florida, where it was refurbished and given an annual inspection. After completion, the helicopter was delivered to the LCSO on October 16, 1996, and placed into service. The last inspection had been completed by the LCSO on September 8, 1999, at 4340.7 hours. The last 300-hour/annual inspection was completed on November 12, 1998, at 4146.0 flight hours. At the time of the accident, the aircraft had accumulated 4419.4 hours. METEOROLOGICAL INFORMATION The Southwest Florida International Airport (KRSW) 0753 surface weather observation was clouds 20,000 feet broken, visibility 10 statute miles, temperature 57 degrees F, dew point temperature 55 degrees F, wind from 040 degrees at 4 knots, altimeter setting 30.10 inches Hg. WRECKAGE AND IMPACT INFORMATION The helicopter crashed into the roof of an animal control building located at 5600 Banner Drive, Fort Myers, Florida, a short distance from the landing pad, located adjacent to the LCSO headquarters building. Examination of the crash site showed that the helicopter came to rest on a bearing of about 210 degrees magnetic, and was wedged into the roof of the building in a nose down attitude with the aft fuselage and tail section intact, protruding out of the top of the roof. Debris from the impact was present on the roof, and around the northeast corner of the building. The nose and pilot compartment of the helicopter exhibited extensive crushing damage. The seats and seat structures, as well as the instrument console were displaced as a result of the impact. The airframe, and the cabin floor exhibited excessive buckling, and had damage consistent with compression overload forces, and the skids had separated from the main fuselage. The main rotor system exhibited damage consistent with a power on flight condition. Three of the four rotor blades separated from the hub assembly, and all four blades exhibited leading edge damage consistent with impact and a sudden stoppage. All main rotor system upper flight controls exhibited damage consistent with an overload condition. Control continuity was confirmed from the cockpit cyclic control to the main rotor system in the longitudinal axis, and from the collective control to the main rotor. The lower rod end of the lateral control from the tunnel routed control tube was found separated, with the rod end still connected to the lateral idler bell crank in the broom closet. The tail rotor system exhibited no damage, and it functioned normally when moved by hand. The tail rotor gearbox rotated smoothly, and when manipulated manually, the pitch change levers moved the tail rotor in a manner consistent with normal operation. The tail rotor gearbox's magnetic chip detector was removed and inspected, and was found to be free of metal. Control continuity from the cockpit directional control pedals to the tail rotor blades was confirmed, but exhibited fractures and bends consistent with an overload condition. The main rotor drive and tail rotor drive systems remained intact except for the engine to main transmission interconnecting drive shaft. The upper and lower drive shaft flex couplings showed overload fractures, consistent with a sudden stoppage. Both main transmission magnetic chip detectors were removed and examined, and found to be free of particles. The transmission exhibited drive continuity to the main rotor and tail rotor systems when turned by hand. The over-running clutch functioned properly when moved by hand after its removal from the engine, rotating freely in the over running direction, and engaging when rotated in the driving direction. The oil tank, oil service lines and gear case contained oil. The engine fuel pump filter was found not installed, and the filter bowl and fuel lines, except for the fuel line in the area of the fire shield to the fuel spray nozzle, contained fuel. The fuel tank contained at least half its capacity of fuel. A vacuum check of the engine fuel system, and a pressure test on engine's pneumatic system revealed no leaks, except for the lower fuel line, from the fuel pump to the fuel control unit, which was slightly crushed at the fuel control unit fitting, and the main fuel line from the airframe to the fuel pump, which had crimp at its midpoint. All other fuel, oil, and pneumatic lines and their fittings were intact and tight. There was no evidence of fuel contamination. The aircraft was equipped with an Allison T63-A700/250-C18 turboshaft engine, serial number CAE-402035, rated for 317 shaft horsepower. On scene examination of the engine showed that there was external crushing damage to the engine, and the engine was displaced to the rear and downward in the engine compartment. The left and right engine mounts were bent, consistent with overload forces such as those from the impact. The exhaust stacks experienced downward crushing and exhibited minor buckling of the lower exhaust support. The left side rear face of the engine's fire shield was bent slightly inward. There was minor damage on the leading edge of two compressor blades on the first stage, but the compressor stage rotated smoothly, freely, and was continuous, through the N1 gearing, to the starter. The power turbine exhibited no visible damage, and rotated freely, smoothly, and was continuous through the N2 gearing, to the output shaft. The engine was retained and shipped to the manufacturer, Rolls-Royce Allison, Indianapolis, Indiana, for further examination. At Rolls-Royce Allison the engine had to be tested to new engine specifications for a C20 engine, since electronic test data was not available, because of the vintage of the engine. Data was first manually plotted to derive performance data for the test, and then the tests were conducted. The test showed that all engine starts, temperatures, pressures, and vibrations were normal, and the engine performed as designed. Derived values were on the plus side at takeoff, and normal cruise settings. MEDICAL INFORMATION The pilot sustained serious injuries, and was admitted to the hospital. No toxicology testing was performed on specimens from the pilot during admission. TESTS AND RESEARCH Federal Aviation Regulations (Parts 21, 39, 43, and 91), and MDHC Service Information Letter HL-124.2, specify that the OH-6A/369A rotorcraft maintenance and inspections be conducted in accordance with applicable military technical manuals, or as specified by MDHC 369 H series maintenance manuals. Records indicate that after receipt of the helicopter from Heli-Tech, it was placed in service by the LCSO, and was maintained and inspected in accordance with the manufacturer's "Basic Handbook of Maintenance Instructions (BHMI)," for the Hughes 369 HS, and "Appendix B: Airworthiness Limitations, Overhaul and Replacement Schedules Periodic Inspections, Weight and Balance Procedures, " to the BHMI, since military technical manuals were not available. In addition to the refurbishment and annual inspection of the helicopter, records also indicate that Heli-Tech inspected and modified the vertical tunnel routed main and tail rotor control tubes, in accordance with FAA Airworthiness Directive 89-23-14, and MDHC Service Information Notice HN-217.1. The lower end of the lateral control rod had been found separated from the control rod during the postcrash examination, and the rod was retained and submitted to the NTSB metallurgical laboratory for analysis. Analysis revealed that the adjustable end of the control rod was bent 17 degrees relative to the axis. The bushing did not move freely, and required considerable effort to rotate by hand. The threaded portions of rivet were in place in the fixed end of the of the rod, but the rivet did not extend through the interior of the fixed end of the rod, nor was any portion of the rivet found in the hole through the threaded portion of the rod end. The internal diameter of the thread portion (minor thread diameter) of the fixed end of the rod was measured at a depth of about 0.2 inches from the end of the rod. Measurements were taken at about 45-degree increments, rotating clockwise starting from the rivet, and they were 0.035, 0.376, 0.374, and 0.384 inches. The outer diameter of the rod end fitting (major thread diameter) was 0.370 to 0.371 inches, measured at a distance up to 0.25 inches on the rod side of the lock nut. The fixed end was cut from the remainder of the control rod and sectioned at about the 90-degree point from the rivet, and the threaded sections were examined using both optical microscopy and scanning electron microscopy (SEM). A significant portion of the thread profile had been worn away, over about one half the length of the threaded region. The thread peaks appeared shiny, and smooth when viewed by optical microscopy, showing evidence of longer term rubbing and wear. A dark deposit was observed between the thread peaks in the worn area. A white deposit was observed in the threaded section starting at a distance of 0.55 inches from the rod end. Examination of the dark and white deposits by energy dispersive x-ray spectroscopy (EDS) revealed similar spectra having peaks that indicate the presence of aluminum and oxygen. The rod end fitting was also examined using optical and scanning electron microscopy. The thread peaks below the lock nuts were slightly worn, and appeared shiny on the rod side of the lock nut, consistent with indications of long term rubbing and wear. A dark deposit was observed between the thread peaks, and a white deposit was observed at the tip of the threaded portion of the fitting. Both the dark and white deposits exhibited peaks representative of aluminum and oxygen in the EDS spectra. ADDITIONAL INFORMATION The aircraft wreckage was released on December 30, 1999, to Captain McKinney, Deputy Sheriff, LCSO. Components which were retained by the NTSB for further testing have also been released to the LCSO.
improper maintenance inspection of the helicopter by unknown maintenance personnel, resulting in a worn control rod bearing being continued in service, and subsequent separation, resulting in an in-flight loss of control and a crash.
Source: NTSB Aviation Accident Database
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