History of Flight
On January 21, 2014, at approximately 1537 central standard time, a Bell 47D-1 helicopter, registered as N93067 and operated by Milam Inc., was substantially damaged during a forced landing near Pell City, Alabama. The commercial pilot and one passenger sustained minor injuries. Day visual meteorological conditions prevailed, and no flight plan was filed for the business flight, which was conducted under Title 14 Code of Federal Regulations Part 91. The flight originated at Birmingham-Shuttlesworth International Airport (BHM), Birmingham, Alabama, at about 1330.
According to the pilot, after meeting his passenger at BHM at 1300, they flew to an area just outside Pell City to inspect a newly installed alarm system and take aerial photographs of the customer's property. After circling the approximately 100-acre property and discussing how to take the photographs, they landed and retrieved a camera from the chin area of the helicopter. The pilot then discussed with the passenger a plan to fly along the property borders for photography. They departed, executed the plan, and returned to the previous landing spot. 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. Due to undulating terrain, the pilot could only extend flight slightly forward, and within about 3 seconds, all available rotor speed was used. The helicopter touched down hard, and one of the wooden main rotor blades struck the tail. The engine continued running but without rotor motion. The pilot then shut off the magnetos and battery switches, and he and the passenger exited.
Personnel Information
Federal Aviation Administration (FAA) and pilot records indicate the pilot held a commercial pilot certificate with ratings for helicopter, airplane single-engine land, airplane multi-engine land, and instrument airplane, along with private pilot privileges for airplane single-engine sea. He also held a flight instructor certificate with a helicopter rating, and a repairman experimental aircraft builder certificate. His most recent FAA second-class medical certificate was issued on April 4, 2013. He reported 4,430 total flight hours, with 1,086 hours in the accident make and model.
Aircraft Information
The accident aircraft was a two-bladed, single-engine light helicopter. According to the FAA registry, it was manufactured by Bell Helicopter Company in 1965 as a Bell model 47D-1, serial number 5501. Maintenance records show the most recent annual inspection was completed on June 9, 2013. The helicopter had accrued approximately 3,980 total hours at the time of the accident.
Review of Bell Helicopter build records by Scott's-Bell 47 revealed that the accident helicopter was not built by Bell or its licensees. Build records indicate that at the time of the listed manufacture in 1965, Bell was producing two production blocks with serial number ranges that did not include 5501. Further review showed no civilian Bell Model 47 with serial number 5501 was delivered by Bell. FAA records revealed that multiple entities manufactured helicopters from Bell spare and surplus parts, and such a helicopter bearing serial number 5501 was listed as a 47D-1 under the name Louis Wm. Cottriel.
Examination of the accident helicopter's data plate revealed multiple overlays. The top displayed "WORLD HELICOPTERS, INC.," with an overlaid layer reading "LOUIS WM. COTTRIEL, BUILDER" and an address in Mineral Wells, Texas. Below were stamped "SERIAL NO. 5501 MODEL 47D-1" and "DATE MFD. May 20, 1965," with the "65" misaligned. Another overlay stated "THIS HELICOPTER MANUFACTURED FROM NEW BELL SPARE AND SURPLUS PARTS." Heavily worn text read "THIS HELICOPTER CONFORMS TO T.C. H-1 SAME AS BELL AIRCRAFT CORPORATION HURST, TEXAS MODEL 47D-1."
NTSB records show the helicopter was involved in five previous accidents (1966, 1982, 1984, 1989, 1992), all resulting in substantial damage. Only two FAA Form 337 major repair forms were on file: one after the first accident (April 1967) and one after the third (January 1985).
Wreckage and Impact
An FAA inspector examined the wreckage and found substantial damage. Approximately 4 feet of the tail section, including the tail rotor, had separated during ground impact. The airframe and skid mounting tubes were bent; the acrylic cockpit bubble was cracked and broken. One main rotor blade showed impact damage, was bent downward, and broken about mid-span.
Examination of the transmission revealed that its data plate indicated it was originally intended for a Bell 47E. The transmission assembly's clutch drum and shoes were not authorized for use in that transmission. The clutch drum displayed abnormal wear grooves, and the clutch shoe lining was glazed with embedded metallic slivers.
Tests and Research
The pilot described his normal clutch engagement procedure, which involved maintaining engine RPM at 1500-1600, noting that clutch engagement was often lengthy. He stated he would sometimes select one magneto off to reduce engine RPM to accelerate the rotor for engagement. The Bell 47D-1 Flight Manual specifies engagement at 1700-1800 RPM after oil pressure reaches 40 psi.
Approximately 15 flight hours before the accident, the pilot had the engine replaced from a Franklin 6V-335 to a 6V-350 by a mechanic in Brewton, Alabama. The mechanic stated no drive train upgrades were required and that he did not disassemble the transmission during installation. He noted the pilot engaged the clutch hard. The mechanic provided FAA Form 337 copies and a flight manual supplement to the pilot.
The transmission had accumulated about 615 hours since overhaul. The Bell 47D-1 Maintenance Manual requires a 600-hour transmission disassembly inspection, but maintenance records did not indicate this inspection had been performed.
FAA records show two Supplemental Type Certificates (STCs) permit the Franklin 6V-350-A installation in Bell 47 helicopters: STC SH479SW (for Bell 47 series) and STC SH529SW (for Bell 47D-1). After STC installation, flight manual supplements must be inserted, a signed original provided to the owner, and a copy sent to the FAA within 48 hours. Examination of FAA records did not indicate whether these requirements were met.