Pell City, AL, USA
N93067
BELL 47D1
The commercial pilot was completing a business flight in the helicopter. He reported that, while descending the helicopter for a confined off-airport landing, at 25 to 35 ft above ground level, he heard a "snap/pop" and that the engine suddenly began "over-revving." The helicopter started descending and then touched down hard, and one of the main rotor blades struck the helicopter's tail. After touchdown, the engine was still running, but the rotor blades were not moving. Examination of the transmission revealed that it incorporated a light-weight clutch assembly, which was not authorized for use in the installed transmission model. Further examination revealed that the clutch shoe running surface on the inner diameter of the clutch drum exhibited a series of abnormal wear grooves along the entire surface of clutch shoe contact and that the clutch lining of each shoe exhibited glazing, which occurs when the clutch is improperly engaged. The contact surface of each clutch shoe also contained numerous metallic slivers that were atypical of a normal in-service clutch assembly and appeared to be material that had transferred from the drum to the shoes. During the transmission examination, the pilot was asked to describe his normal engine start and clutch engagement procedure. The clutch engagement procedure described by the pilot was not in accordance with the published procedure. The pilot's procedure likely resulted in a lengthy clutch engagement and an extended period of clutch slippage during each start that led to the glazed condition of the clutch assembly. Once the glazed condition began to develop, the period of clutch slippage during each start lengthened, further contributing to the glazed condition. Ultimately, the glazed condition resulted in the in-flight disengagement of the clutch and a loss of rotor rpm. The pilot reported that, about 15 flight hours before the accident, he had a mechanic install an engine in the helicopter that produced 25 more horsepower than the previously installed engine. The installation of the higher horsepower engine would have increased the tendency for slippage of a glazed clutch assembly. The pilot also reported that the transmission had accumulated about 615 hours since overhaul. According to the helicopter's maintenance and overhaul instructions, the transmission should be disassembled every 600 hours to inspect all parts, including the clutch, for damage or excessive wear. Given that the engine had been installed about 15 flight hours before the accident, the 600-hour inspection could have been accomplished at that time. However, review of maintenance records did not indicate that the 600-hour transmission inspection had occurred, and the mechanic who installed the higher horsepower engine reported that he did not disassemble the transmission.
HISTORY OF FLIGHT On January 21, 2014, about 1537 central standard time, a Bell 47D-1, N93067, operated by Milam Inc. was substantially damaged during a forced landing near Pell City, Alabama. The commercial pilot and one passenger received minor injuries. Day, visual meteorological conditions prevailed, and no flight plan was filed for the business flight, operated under the provisions of Title 14 Code of Federal Regulations Part 91, which originated at Birmingham- Shuttlesworth International Airport (BHM), Birmingham, Alabama about 1330. According to the pilot, after meeting his passenger at BHM at 1300 they flew to an area just outside of Pell City, Alabama to look at a newly installed alarm system and to take some aerial photographs of the customer's property. After flying around the property which covered approximately 100 acres, and discussing how they could take the photographs, they landed and retrieved a camera from the "chin area" of the helicopter. The pilot then discussed with the passenger how he could fly along the borders of the property so the passenger could take the photographs he desired. They then departed and flew "the plan" they had discussed, and then returned to the spot where they had landed before. While descending into the confined area for landing, at 25 to 35 feet above ground level, the pilot heard a "snap/pop" and the engine suddenly began "over-revving." The helicopter began descending, and due to the undulating terrain that was below them the pilot could only extend the flight slightly forward, and within approximately 3 seconds, he had used up all of the available rotor speed. The helicopter then touched down hard and one of the wooden main rotor blades struck the tail of the helicopter. The engine was still running but with no rotor motion. The pilot then shutoff the magnetos and battery switches, and he and the passenger exited the helicopter. PERSONNEL INFORMATION According to Federal Aviation Administration (FAA) and pilot records, the pilot held a commercial pilot certificate with ratings for helicopter, airplane single-engine land, Airplane multi-engine land, and instrument airplane, with private pilot privileges for airplane single-engine sea. He also held a flight instructor certificate with a rating for helicopters, and repairman experimental aircraft builder certificate, with an inspection certificate for an experimental Rotorway Executive helicopter he had built. His most recent FAA second-class medical certificate was issued on April 4, 2013. He reported that he had accrued 4,430 total hours of flight experience, 1,086 of which were in make and model. AIRCRAFT INFORMATION The accident aircraft was two-bladed, single engine, light helicopter which according to the FAA registry was manufactured by Bell Helicopter Company in 1965 as a Bell model 47D-1, serial number 5501. According to maintenance records, the helicopter's most recent annual inspection was completed on June 9, 2013. At the time of accident, the helicopter had accrued approximately 3,980 total hours of operation. Bell 47 History and Build Records On March 8, 1946, the Bell 47 was certificated for civilian use by the Civil Aeronautics Administration. More than 5,600 were produced with the helicopter being manufactured in the United States, and under license in Italy, Japan, and the United Kingdom. Review of Bell Helicopter Company build records by Scott's-Bell 47, which purchased the type certificate from Bell Helicopter Textron in 2010, revealed that despite what was recorded in the FAA registry, the accident helicopter was not built by Bell Helicopter Company or any of its licensees. According to build records, at the time that the accident helicopter was listed as being manufactured in 1965, Bell Helicopter was manufacturing two production blocks of helicopters, with serial numbers 3958 through 4013, being built as OH-13 models for the United States Army, and serial numbers 6501 thru 6513, being built as 47G-3B-1 models, for the commercial market. Bell produced no helicopters during that time period bearing serial numbers within the gap (4014 thru 6500) which existed between the two production blocks, which would have encompassed manufacturer's serial number 5501. Further review of build records also revealed that no civilian Bell Model 47 was ever delivered bearing the serial number 5501 by Bell, nor were there any military Bell helicopter models similar to the model 47 under any year of manufacture, that would have been assigned a sequential serial number and/or military ship number by Bell or the military services, which would have consisted of the 2-digit year of manufacture, and military serial number that could have been similar to the 5501 serial number on the accident helicopter. FAA Certification Data Review of FAA Type Certificate Data Sheets (TCDS) and a search of FAA's Electronic Data Retrieval System (EDRS) revealed that with Federal Aviation Agency (Successor to the CAA, which later became the Federal Aviation Administration under the Department of Transportation) approval, a number of entities "manufactured" helicopters from Bell spare and surplus parts, which the Federal Aviation Agency issued airworthiness certificates for, and then classified as Bell 47s in the registry, though Bell had not manufactured them as the type certificate holder. These included approximately: - 20 entities who had manufactured Bell 47D-1 models. - 16 entities who had manufactured Bell 47G models. - 9 entities who had manufactured Bell 47G-2 models. Further review of FAA TCDS and FAA EDRS data indicated that a helicopter manufactured as a 47D-1 bearing serial number 5501, was listed as an aircraft eligible for designation as a 47D-1, under the name of Louis Wm. Cottriel. Identification (Data) Plate According to the FAA, Each manufacturer of aircraft, aircraft engines, propellers, and propeller blades and hubs is required to display the following information on a fireproof plate, by means of stamping, engraving, etching, or another approved method: (1) The builder's name, which may be the name of an individual, firm, co-partnership, corporation, company, association, or joint-stock association. (2) Model designation. (3) Builder's serial number. (4) TC number, if any. (5) Production certificate (PC) number, if any. (6) For aircraft engines, the established rating. (7) For aircraft engines, the date of manufacture, that is, month (two digits)/ year (four digits). (8) For aircraft engines, the engine's approved 14 CFR part 34 designations. (Part 34 discusses fuel venting and exhaust emission requirements for turbine engine-powered airplanes.) Approved designations include comply, exempt, and non-U.S. for engines specified in part 34, manufactured on or after January 1, 1984. The fireproof plate is required to be placed on a surface where it is not likely to be defaced or removed during normal service. The identification cannot be placed on an inspection plate, or removable fairing. On aircraft manufactured before March 7, 1988, the identification plate is required to be mounted on an interior or exterior location near an entrance, so that it is legible from the ground either just behind and next to the rear-most entrance door or on the underside of the fuselage near the tail surface. The model and serial numbers also are required to be displayed on the fuselage exterior. In regards to identification plate requirements for aircraft built from spare or surplus parts, In addition, to the requirements listed above, the following guidelines should be followed: (1) Use the builder's name as the name (the person who assembled the aircraft), not the name of the manufacturer who builds the same model of aircraft. (2) Assign any serial number if it is clear that the manufacturer who builds the same model of aircraft did not assign an identical number. A letter prefix or suffix should also be added such as a name or initials, to the serial number to provide positive identification. Examination of the accident helicopter's data plate revealed however that even though it had the basic information required, it had been modified with multiple overlays: - Starting at the top of the data plate, the name "WORLD HELICOPTERS, INC." was displayed. - Just below that was an overlaid layer on the data plate with the words "LOUIS WM. COTTRIEL, BUILDER" with an address in Mineral Wells, Texas. - Below that stamped into the original data plate was; "SERIAL NO. 5501 MODEL 47D-1." - Below that stamped into the data plate was; "DATE MFD. May 20, 1965." The "65" however was printed with the numbers "65" not aligned with the "19" on the data plate with the "5" appearing to be smudged. - Below that stamped into the data plate was; "ENGINE FRANKLIN." - Below that stamped into the data plate was; "ENGINE SERIAL NO." but no engine serial number was listed. - Another overlay was below this which covered two other stamped data blocks in the data plate. Printed on the overlay were the words "THIS HELICOPTER MANUFACTURED FROM NEW BELL SPARE AND SURPLUS PARTS." - Below that, printed on the date plate, heavily worn and almost illegible, were the words; "THIS HELICOPTER CONFORMS TO T.C. H-1 SAME AS BELL AIRCRAFT CORPORATION HURST, TEXAS MODEL 47D-1" Previous Accident History Review of NTSB records revealed that the helicopter had been involved in 5 previous accidents: - The first accident occurred on September 1, 1966 (NTSB Case No. LAX67A0026), when the helicopter was substantially damaged after the helicopter developed a high sink rate and the pilot did not attempt a power recovery. - The second accident occurred on May 20, 1982 (NTSB Case No. FTW82DA189), when the helicopter was substantially damaged during an aerial application flight, when the pilot turned downwind and the tail rotor struck a rice dike. The pilot lost control and the helicopter landed hard. During the hard landing, the main rotor severed the tail boom. - The third accident occurred on November 3, 1984 (NTSB Case No. FTW85LA043), when the helicopter was substantially damaged on a sightseeing flight when the engine lost power over rough terrain at approximately 220 feet above ground level. During the touch down after the autorotation, the helicopter rocked forward and the main rotor blades struck the tail boom. - The fourth accident occurred on November 2, 1989 (NTSB Case No. MIA09LA023), when the helicopter was substantially damaged during an aerial application flight, the pilot pulled up and held back longer to clear trees at the end of the field. The helicopter lost airspeed faster than the pilot realized and the helicopter descended and impacted trees. - The fifth accident occurred on June 27, 1992 (NTSB Case No. MIA92LA069), when the helicopter was substantially damaged after a loss of engine power while maneuvering. The pilot was unable to maintain altitude and he performed an autorotation into trees. Review of FAA Airworthiness records revealed however that only two FAA 337 Major Repair and Alteration (Airframe, Powerplant, Propeller, or Appliance) forms, were on file with the FAA: - The first was filed on April 10, 1967 after the first accident and it described the description of the work accomplished to repair the helicopter and return it to service, including replacement of the center frame, repair of the tail boom, patching of the bubble (windscreen), and replacement of the engine mount, tail rotor hub, tail rotor blades, main rotor blades, transmission, and tail rotor gearbox. - The second was filed on January 12, 1985 after the third accident and it described the description of the work accomplished to repair the helicopter and return it to service, including the repair made to the tail boom. Review of the FAA EDRS records revealed no other records describing the description of work accomplished to repair the helicopter and return it to service after the other three accidents it was involved in (NTSB Case Numbers; FTW82DA189, MIA09LA023, and MIA92LA069). METEOROLOGICAL INFORMATION The recorded weather at Anniston Metropolitan Airport (ANB), Anniston, Alabama, located 22 nautical miles east of the accident site, at 1553, included: winds 300 degrees at 8 knots, gusting to 19 knots, 10 miles visibility, overcast clouds at 3,500 feet, temperature 01 degrees C, dew point - 07 degrees C, and an altimeter setting of 30.03 inches of mercury. WRECKAGE AND IMPACT INFORMATION Wreckage Examination Examination of the wreckage by a Federal Aviation Administration (FAA) inspector revealed that the helicopter was substantially damaged. Approximately 4 feet of the tail section including the tail rotor had separated from the helicopter during the ground impact. The airframe and skid mounting tubes were bent; the acrylic cockpit bubble was cracked and broken. One blade of the two blade main rotor system displayed impact damage, was bent downward, and was broken about mid-span. Transmission Examination The transmission assembly, which was mounted on an adapter plate at the upper end of the engine, was a speed-reducing mechanism for driving the main rotor, cooling fan, generator, tail rotor, and rotor tachometer generator. The cylindrical case was composed of a series of castings and rings held together by through bolts. The main rotor mast support bearing was mounted in the top of the upper section. Four drive assemblies, which drive the tail rotor drive shaft, cooling fan, generator, and rotor tachometer generator, were mounted to the lower section of the case. Internally, the assembly consisted of a centrifugal clutch, freewheeling unit, a two-stage planetary reduction gear train, spiral bevel gear to drive the tail rotor drive assembly, and a bevel gear to drive the cooling fan. The centrifugal clutch relieved the starter of the rotor load during starts and permitted rotation of the rotor manually for inspection without turning the engine. The freewheeling unit made possible autorotation landings with an idling or dead engine. The generator, tail rotor drive, and rotor tachometer generator were driven whenever the main rotor was in motion (power on, or power off). This made it possible for the pilot to have complete control of the helicopter during autorotation landings. Examination of the transmission revealed that the data plate affixed to the transmission contained information that the transmission assembly was originally meant for installation in a Bell 47E. The data plate contained part number 47-620-600; the original dash number ("9") was still visible though the data plate had been over-stamped with the number "17". Transmission serial number 3346 was clearly visible in the reserved block. Review of FAA TCDS revealed that the TCDS listed Bell helicopter serial number block from 165-173 as eligible for designation as a Bell 47E, Bell records revealed however that these serial numbers were built as Bell HTL-3 helicopters and were delivered to the US Navy in 1950 and 1951. Bell records indicated that only one Model 47E was actually certificated for commercial sale and it was delivered in December, 1951. After removing the transmission assembly from the engine adapter plate, free access was gained to the engine-transmission drive ring. Manual force applied to the drive ring confirmed that the drive ring was secure in place on the upper end of the engine crankshaft and it was able to transmit engine power to the main transmission. The transmission case assembly's through bolts were removed, and the upper case assembly was removed exposing the upper spider assembly. The upper spider assembly, consisting of the upper planetary gear reduction and main rotor drive flange; case assembly spacer, freewheel assembly, and lower spider assembly, were removed from the transmission assembly. These assemblies exhibited no unusual condition and the freewheel assembly operated normally. The main case assembly was inverted and supported on support fixture to facilitate removal of the clutch assembly. The clutch drum retainer nut was still locked in place with two lock-wired fillister head screws with a straight screwdriver head slot. The lock wire
The pilot’s use of an improper clutch engagement procedure, which resulted in clutch glazing, slippage, and, ultimately, the in-flight disengagement of the clutch and a loss of rotor rpm. Contributing to the accident were the installation of a light-weight clutch assembly and a higher horsepower engine, both of which increased the tendency for clutch slippage, and inadequate inspection of the clutch assembly.
Source: NTSB Aviation Accident Database
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