WEBSTER, FL, USA
N598F
Hiller FH-1100
The helicopter (N598F) was flying at about 750 to 1,000 ft, when witnesses heard a loud noise, then saw N598F descending & spinning to the right. N598F impacted the ground upright at the edge of a pond. Postcrash exam showed that a tail rotor blade had separated in flight, followed by the other tail rotor blade, hub, & gearbox. Metallurgical exam showed the tail rotor blade had separated due to fatigue fractures in 9 of 11 plates in the tail rotor blade torsion tension (TT) bar. Fatigue originated at machining discontinuities on the inner surfaces of eye holes at the bushing ends, which had been punched in the plates during the manufacturing process. In 1977, Airworthiness Directive (AD) 77-07-08 & Fairchild Hiller Service Bulletin (SB) FH1100-55-2A were issued to inspect for this problem. Records of N598F showed the AD & SB had been complied with on 3/9/77, but the tail rotor assembly had been removed & replaced with another assembly on 3/17/83. Records did not show if the AD & SB had been complied with on the replacement tail rotor assembly. Overhaul procedures did not allow disassembly of the TT bar to examine the holes. Weight & balance calculations showed that after tail rotor separated, the center of gravity moved about 2.1 inches forward of the forward limit. FH-1100 emergency procedure for tail rotor failure required that the pilot immediately reduce engine power to zero torque & perform an autorotative landing. Throttle was found in full power range. Helicopter was not equipped with shoulder harnesses.
HISTORY OF FLIGHT On June 28, 1996, about 1310 eastern daylight time, a Hiller FH-1100, N598F, registered to TBH, Inc., crashed near Webster, Florida, while on a 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft received substantial damage and the commercial-rated pilot and one passenger were fatally injured. The flight originated from Odessa, Florida, the same day, about 1230. Witnesses observed the helicopter flying from the southwest to the northeast at about 750 to 1,000 feet. They heard a loud "bang" similar to the hood of a car being slammed and observed the helicopter descending with the fuselage spinning around in a clockwise direction. The helicopter was making a "whoop whoop whoop" noise. The helicopter crashed at the edge of a pond while in the spinning descent. PERSONNEL INFORMATION Review of the pilot's most recent logbook, which started on March 22, 1993, and was identified as logbook 5, showed the pilot had accumulated about 2,112 total flight hours, with 814 flight hours in airplanes and 1,298 flight hours in helicopters. This logbook showed the pilot had 690 flight hours in turbine powered helicopters, of which 131 flight hours were in the Hiller FH-1100. The pilot's family did not submit logbooks 1 through 4 to NTSB for review as requested. The pilot's total flight hours in the FH-1100 and flight training received in the FH-1100 could not be determined. Additional information on the pilot is contained in this report under First Pilot Information. AIRCRAFT INFORMATION A review of aircraft maintenance records showed the aircraft was last inspected on May 9, 1996, when it received an annual inspection, at aircraft total time 3,846 hours. The Hobbsmeter was not located after the accident and it was estimated by the aircraft operator that the helicopter had flown about 10 flight hours since the inspection until the accident. A review of maintenance records for the tail rotor assembly showed the assembly was installed on N598F on March 17, 1983, at aircraft total time 2,988 hours. The assembly had been removed from another helicopter and had accumulated 769 total flight hours since new. On October 20, 1986, the tail rotor assembly was removed, overhauled, and reinstalled on N598F, at aircraft total time 3,345 hours. On December 10, 1986, 10 flight hours after overhaul, the tail rotor assembly was removed and inspected for damage from a tail rotor strike, and reinstalled on N598F. At the time of the accident, the tail rotor assembly had accumulated about 511 flight hours since overhaul. For additional aircraft information see Aircraft Information in this report and maintenance records attached to this report. WEIGHT AND BALANCE INFORMATION Weight and balance calculations showed that before separation of the tail rotor assembly the helicopter weighted about 2,460 pounds and the center of gravity was about 96.77 inches aft of the datum. According to the helicopter manufacturer, separation of the tail rotor assembly and gearbox would remove about 33 pounds from station 347.5. This would change the helicopters weight to 2,427 pounds and the center of gravity to 93.36 inches aft of the datum at the time of the accident. The maximum allowable weight for the helicopter is 2,750 pounds and the allowable center of gravity range is from 95.5 inches aft of the datum forward limit and 101.5 inches aft of the datum rear limit. (See attached weight and balance information). METEOROLOGICAL INFORMATION Visual meteorological conditions prevailed at the time of the accident. For additional meteorological information see Weather Information in this report. WRECKAGE AND IMPACT INFORMATION The helicopter crashed at the edge of a pond located on a farm at 12636 Southeast 50th Street, Webster, Florida. The crash site was located at latitude 28 degrees, 34 minutes north and longitude 82 degrees, 01 minutes west. Examination of the crash site showed the helicopter had come to rest on a northerly heading in about 2 feet of water at the edge of the pond. The tail rotor gear box, tail rotor hub assembly, and part of one still attached tail rotor blade was located about 200 yards west of the crash site. The other portion of this rotor blade was not located. The complete second tail rotor blade was located about 300 yards west of the crash site. All other components of the helicopter which are necessary for flight were located on or around the main wreckage of the helicopter. Examination of the helicopter structure showed the helicopter had impacted the ground while in a left bank and came to rest upright. The front windscreen separated upon impact. The left front lap seatbelt had been cut by rescue personnel. The helicopter was not equipped with shoulder harnesses. The right front seatbelt came loose when the inboard attach fitting separated due to overstress. The right seat engine throttle on the right collective control was found in the full power position. The main rotor blades were in place and had no rotational damage. One blade was bent downward about 3 feet from the tip. There was no damage to indicate the main rotor blades had contacted the helicopter structure. Examination of the flight control systems showed there was continuity within the cyclic and collective control systems from the cockpit controls to the main rotor head. The separation points within these systems were typical of overstress separation. Examination of the anti-torque control system showed there was continuity of the control cables from the cockpit pedals to the point the chain wrapped around the tail rotor 90-degree gearbox gear at the vertical fin. The separation points along the cables and chain were typical of overstress separation. Examination of the engine and transmission showed that the engine rotated freely and there was no damage to the compressor and turbine wheels. All drives from the engine turned when the engine was rotated by hand. The main driveshaft between the engine and transmission was in place and rotated normally. The main transmission and rotor head turned freely and all drives from the transmission turned. The tail rotor driveshaft turned freely from the engine area to the 45-degree gearbox. The 45-degree gearbox rotated freely. The tail rotor driveshaft section, which ran along the front side of the vertical fin between the 45-degree gearbox and 90-degree gearbox, was found lying about 20 feet east of the main wreckage. The driveshaft cover had separated and was not located. The driveshaft had scoring damage at points along its length which coincided with components mounted on the vertical fin. The 90-degree gearbox and its mounting had separated from the vertical fin. The separation point had features typical of overstress. Examination of the tail rotor 90-degree gearbox and hub assembly, which was still mounted to the gearbox along with the inboard end of one tail rotor blade, showed the gearbox and hub rotated freely. The second tail rotor blade had separated from the hub at the tension-torsion bar. The portion of tail rotor blade which remained attached to the hub showed the blade outboard section separated through the airfoil section. The separation point showed damage consistent with overstress separation. None of the recovered tail rotor components had damage consistent with bird or foreign object impact. MEDICAL AND PATHOLOGICAL INFORMATION Postmortem examination of the pilot and passenger was performed by Dr. Janet R. Pillow, Associate Medical Examiner, Leesburg, Florida. The cause of death was attributed to multiple injuries sustained in the accident. No findings which could be considered causal to the accident were report. Postmortem toxicology tests on specimens obtained from the pilot were performed by the Medical Examiner's Office, Leesburg, Florida, and the Federal Aviation Administration, Oklahoma City, Oklahoma. The tests were negative for ethanol alcohol, carbon monoxide, basic, acidic, and neutral drugs. The tests were positive for less than 10 ng/ml diazepam. Postmortem toxicology tests on specimens obtained from the passenger were performed by the Medical Examiner's Office, Leesburg, Florida. The tests were negative for ethanol alcohol, carbon monoxide, basic, acidic, and neutral drugs. For additional medical and pathological information see Supplements K and the toxicology tests report. TESTS AND RESEARCH On January 19, 1977, Fairchild Hiller Helicopter issued Alert Service Bulletin SBFH1100-55-2A, titled Tail Rotor Assembly Special Inspection of Tension-Torsion Bar Assemblies prior to S/N 1922. The reason for the bulletin was "to remove from service and spares all tension-torsion bar assemblies found unacceptable by this inspection. This bulletin describes the procedures to be used in inspecting the material condition around the circumference of the attachment holes at each end of the P/N 24-55107 T.T. straps." It was recommended that the one-time procedure be performed on all installed T.T. bar assemblies within the next 25 flying hours and that all spare new and used T.T. bars be inspected before installation. If the inner surface of the hole is found to be broken with transverse tool marks or if pitting or damage that breaks through one edge is found, the bars are to be rejected. The Federal Aviation Administration issued Airworthiness Directive 77-07-08 on August 5, 1977, requiring the accomplishment of SBFH1100-55-2A on all model 1100 and FH-1100 helicopters within the next 25 hours. (See SBFH1100-55-2A and AD 77-07-08). The tension-torsion bar which failed and allowed separation of one tail rotor blade on N598F was serial number 1177. The tension-torsion bar which retained the inboard portion of the second tail rotor blade to the hub was serial number 1320. Logbook records showed AD 77-07-08 and SBFH1100-55-2A was complied with on N598F on March 9, 1977. The tail rotor assembly installed on the helicopter at that time was removed and replaced with the accident hub assembly on March 17, 1983. Records did not show if AD 77-07-08 and SBFH1100-55-2A had been complied with on the accident hub assembly. (See maintenance records). Fairchild Hiller overhaul procedures for the tail rotor assembly state that no disassembly of the tension-torsion bar is permissible. Overhaul procedures require that the tension-torsion bar be inspected as follows. "Use a 4X magnifying glass to accomplish a close visual inspection of the exposed portions of the tension-torsion plates (laminations), two end bushings, and the bushing collars for sharp nicks, scratches, or evidence of cracks. Pay particular attention to the plate edges around and adjacent to the ends of the assembly." Overhaul procedures do not call for inspection of the inner diameter surface of the bar holes. Logbook records showed the accident tail rotor assembly was overhauled on October 20, 1986, 511 flight hours before the accident. (See overhaul manual pages and maintenance records). The Fairchild Hiller FH-1100 Flight Manual, Emergency Procedures for Tail Rotor Failure state "immediately reduce engine power to zero torque, establish an autorotative airspeed of at least 70 MPH and execute a full autorotative landing." The engine throttle on N598F was found in the full power position after the accident. (See Flight Manual page). METALLURGICAL EXAMINATION Metallurgical examination of the separated tail rotor blade, hub assembly, and 90 degree gearbox, was performed by Joe Epperson, NTSB Materials Laboratory, Washington, D.C. The examination showed the complete tail rotor blade which had separated from the hub had separated due to fatigue cracking of the tension-torsion bar plates. The fatigue cracking initiated at discontinuities in the hole area which was a result of manufacturing operations. (See Metallurgist's Factual Report.) ADDITIONAL INFORMATION The aircraft wreckage was released to Mr. Michael Wilhelms, Senior Claims Representative, COMAV Managers, St. Peters, Missouri, on July 10, 1996. All components retained for examination were returned to Mr. Wilhelms on June 12, 1997.
inadequate compliance with AD 77-07-08 (and SB FH1100-55-2A) by other maintenance personnel, and subsequent fatigue failure of plates in the tail rotor torsion tension bar. Factors related to the accident were: manufacturing discontinuities (scoring/indentations) in holes of plates of the tail rotor torsion tension bars, and failure of the pilot to follow emergency procedures (reduce power to attempt an autorotative landing, following loss of the tail rotor assembly).
Source: NTSB Aviation Accident Database
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