MARATHON, FL, USA
N9660
BELL 47D1
WITNESSES HEARD A LOUD NOISE AS THE HELICOPTER WAS FLYING AT 100' TO 150' AGL & SAW SOMETHING FALL FROM THE TAIL BOOM. THE HELICOPTER IMMEDIATELY NOSED DOWN & BEGAN SPINNING TO THE RIGHT. IT IMPACTED ON A ROCK ISLAND & CAME TO REST IN WATER NEXT TO THE ISLAND. THE TAIL ROTOR GEARBOX, TAIL ROTOR HUB & ONE TAIL ROTOR BLADE WERE NOT LOCATED AFTER THE ACCIDENT. ONE TAIL ROTOR BLADE WAS FOUND ALONG THE FLIGHTPATH IN 2 PIECES, ABOUT 150' FROM THE MAIN WRECKAGE. THE TAIL ROTOR GEARBOX HAD SEPARATED DUE TO OVERSTRESS; ALL FRACTURES OF THE RECOVERED TAIL ROTOR BLADE WERE TYPICAL OF OVER- STRESS. THE TAIL ROTOR BLADE HAD NO IMPACT MARKS ON THE LEADING EDGE OR TIP. NO PRECRASH FAILURE/MALFUNCTION OF THE REMAINING STRUCTURE, FLIGHT CONTROLS, MAIN ROTOR BLADES, TRANSMISSION OR ENGINE WAS FOUND. A TAIL ROTOR STRIKE OCCURRED 130 FLIGHT HRS BEFORE THE ACCIDENT; THE TAIL ROTOR BLADES WERE CHANGED, BUT THE HUB WAS NOT CHANGED AS REQUIRED BY THE MANUFACTURER'S INSTRUCTION. THOUGH OPERATING FOR HIRE, HELICOPTER HAD FLOWN 130 HRS SINCE THE LAST MAINTENANCE INSPECTION. CALCULATIONS SHOWED THAT DURING TAKEOFF, THE HELICOPTER'S CG WAS 3.4' FORWARD OF THE FORWARD LIMIT. WITH LOSS OF THE SEPARATED PARTS, THE CG WOULD HAVE MOVED ABOUT 2' FURTHER FORWARD.
HISTORY OF FLIGHT On April 22, 1994, about 1128 eastern daylight time, N9660, a Bell 47D1, registered to New Tropical Adventures, Inc., crashed while approaching to land at Marathon, Florida, while on a 14 CFR Part 91 sightseeing flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The helicopter was destroyed and the commercial-rated pilot received serious injuries. Two passengers were fatally injured. The flight originated at Marathon, Florida, moments before the accident. Witnesses observed the helicopter flying at about 100 to 150 feet agl. They heard a loud "bang" or "explosion" and observed something separate from the tail of the helicopter. The nose of the helicopter dropped down and the helicopter started to yaw to the right as viewed from the pilot seat. The helicopter yawed around two to three times, descended, and impacted on Vaca Key Rock. After impact the helicopter bounced up, began to disintegrate, and went off the island into the water. PERSONNEL INFORMATION Review of the pilot's logbook indicated the pilot had 677 total flight hours, all in rotorcraft helicopters. The pilot first flew the Bell model 47 on January 2, 1994, for .3 hours solo familiarization. The pilot flew two additional solo familiarization flights for .3 hours each on January 12, 1994, and February 18, 1994. On February 19, 1994, the pilot received 1.1 hours of dual instruction in the Bell model 47. Autorotations, hovering, hydraulic failure, and familiarization were listed as the items covered. No flight instructor signature or name was listed. The logbook shows no other familiarization, dual instructional, or checkout flights in the Bell model 47. For additional pilot information see the First Pilot Information section in this report and the pilot logbook pages attached to this report. AIRCRAFT INFORMATION Aircraft maintenance records indicated the aircraft received a 50-hour inspection on March 10, 1994, 105 flight hours before the accident. This was the last entry in the aircraft records. The aircraft last received an annual and 100-hour inspection on July 1, 1993, 152 flight hours before the accident. Federal Aviation Regulations require that an aircraft carrying persons for hire must have received an annual or 100-hour inspection within the preceding 100 hours of time in service. Aircraft maintenance records indicated that on August 26, 1993, 130 flight hours before the accident, the tail rotor blades were found to have damage at the tip and the tailrotor guard upper bracket was found cracked. The blades and bearings were changed and balanced and a clamp was placed on the bracket as a temporary repair. A tailrotor strike inspection was performed. Bell Helicopter Maintenance and Overhaul Instructions require that the tailrotor hub be replaced at any time tailrotor blades are changed due to damage. Logbook records did not indicate that this was accomplished. For additional aircraft information see the Aircraft Information section in this report and attachments to this report. METEOROLOGICAL INFORMATION Visual meteorological conditions prevailed at the time of the accident. Additional meteorological information is contained in this report under Weather Information. WEIGHT AND BALANCE INFORMATION Aircraft weight and balance records, dated January 20, 1991, indicated the helicopter had an empty weight of 1,536.3 pounds and an empty center of gravity of 2.05 inches aft of the datum. Using this information the takeoff condition for the accident flight was determined to be 2,052.3 pounds and a center of gravity at 5.4 inches forward of the datum. The maximum weight for the aircraft is 2,200 pounds and the center of gravity limits are 2.0 inches forward of the datum and 2.9 inches aft of the datum. Bell Helicopter representatives indicated that the tailrotor and tailrotor gear box have a combined weight of 16 pounds at an arm of 260 inches aft of the datum. Loss of these components would move the center of gravity forward 2 inches, or in the accident helicopter to 7.4 inches forward of the datum and 5.4 inches forward of the maximum limit. (See attached weight and balance record.) WRECKAGE AND IMPACT INFORMATION The aircraft crashed on Vaca Rock Key, which is north of the 12,000 block of Overseas Highway, Marathon, Florida. Examination of the crash site indicated the helicopter crashed on the rock island while upright on a 210-degree heading. The right skid impacted first. General disintegration occurred after this and the main wreckage came to rest in the water just off the island to the northeast. All components of the helicopter were located on or around the main wreckage except for the tailrotor gearbox, tailrotor hub, and both tailrotor blades. One piece of a tailrotor blade was found in the water 130 feet southwest of the key, along the helicopter's flight path. Another piece of a tailrotor blade was found 50 feet northwest of this piece. Examination of the helicopter structure and flight control systems indicated that all separations of structure and flight control linkages were indicative of overstress separation. A portion of the tailrotor gearbox housing was still bolted to the tail boom. Metallurgist's examination of this portion of tailrotor gearbox indicated the separation was typical of overstress separation with no evidence of progressive failure. The remainder of the tailrotor gearbox, tailrotor hub, and one tailrotor blade were not located after the accident. Examination of the two pieces of tailrotor blade which were found about 150 feet from the main wreckage and 50 feet apart indicated that they formed one tailrotor blade. The grip end of the blade was separated and not recovered. The blade had not sustained impact damage along the leading edge or tip. Impact damage had occurred along the inboard side near the grip end. A fracture had occurred near the mid area of the blade, separating the blade into two pieces. All fractures were indicative of overstress separation. Examination of the engine indicated that it rotated normally and the valve train and accessory drives operated normally. Each cylinder produced compression. Each spark plug had a light gray carbon deposit on it. The right magneto produced spark when rotated. The left magneto was destroyed by impact forces. The carburetor bowl was free from contamination and all jets and ports were unobstructed. The float and fuel shutoff valve operated normally. The airframe fuel strainer contained some aviation fuel and was free of debris. The engine cooling fan had sustained rotational damage. Examination of the main rotor blades indicated each blade had sustained rotational damage. All blade weights were located in the blades. The leading edge of one blade had red paint transfer and impact damage which matched an impact mark on the tailboom. The main transmission rotated freely and all drives from the transmission operated normally. The free wheeling clutch operated normally. For additional wreckage and impact information see attachments to this report. MEDICAL AND PATHOLOGICAL INFORMATION The pilot sustained serious injuries as a result of the accident. The pilot's attorney indicated that the pilot's medical condition precluded him from being interviewed or submitting any information about the flight. Toxicology testing of specimens obtained from the pilot on admission to the hospital shortly after the accident was performed by Dennis V. Canfield, Ph.D., Federal Aviation Administration, Oklahoma City, Oklahoma. The tests were negative for ethanol alcohol, basic, acidic, and neutral drugs. The two passengers received fatal injuries as a result of the accident. Post-mortem examination of the two passenger was performed by Hugo Romeu, M.D., Associate Medical Examiner, Marathon, Florida. The cause of death was due to injuries sustained in the accident. Toxicology testing on specimens obtained from the two passengers was performed by B. Capshaw, Wuesthoff Hospital Laboratory, Marathon, Florida. The tests were negative for ethanol alcohol, acidic, basic, and neutral drugs. For additional medical and pathological information see Supplement K and the toxicology reports attached to this report. ADDITIONAL INFORMATION The aircraft wreckage was released on April 25, 1994, to Charles G. Maynard, Sample International, Ormond Beach, Florida. Components which were retained by NTSB for further examination were released to Charles G. Maynard on August 24, 1994.
SEPARATION OF THE TAIL ROTOR GEARBOX AND TAIL ROTOR BLADES FOR AN UNDETERMINED REASON. FACTORS RELATED TO THE ACCIDENT WERE: FAILURE OF MAINTENANCE PERSONNEL TO FOLLOW THE PROPER MAINTENANCE PROCEDURE AFTER A PREVIOUS TAIL ROTOR STRIKE, AND FAILURE TO CONDUCT A 100-HOUR INSPECTION WHEN DUE.
Source: NTSB Aviation Accident Database
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