NTSB Factual Report

HISTORY OF FLIGHT

On August 4, 2004, at an unknown time, a Bell 47G-5 helicopter, N232MC, registered to and operated by East Flagler Mosquito Control District, as a Title 14 CFR Part 137 aerial application flight, crashed while maneuvering in Flagler County, Florida. Visual meteorological conditions prevailed, and a company flight plan was filed. The commercial-rated pilot received fatal injuries, and the helicopter was substantially damaged.

The director of East Flagler Mosquito Control District stated that the flight originated from Flagler County Airport, Bunnell, Florida. This was the fifth aerial application flight of the day. At approximately 1030, the helicopter was fueled and flew north to an area called Pellicer Flats to spray mosquito control products. After it was determined to be 45 minutes overdue and could not be contacted, search efforts were initiated. Flagler Emergency Services immediately launched their helicopter as part of the search effort. At 1300, the aerial application helicopter was located approximately 12 miles north of Flagler County Airport, in a marshy/grassy area, just west of the intercoastal waterway in Palm Coast, Florida. The wreckage lay in about 2 feet of water.

PERSONNEL INFORMATION

Records obtained from the FAA show that the pilot held a commercial pilot certificate with rotorcraft helicopter and instrument helicopter ratings. He also held a private pilot certificate, with airplane single engine land and instrument airplane ratings. He held an FAA second-class medical certificate, issued on November 21, 2003, with no stated limitations.

According to the pilot's logbook, the pilot had accumulated 967 hours of total flight experience, of which 232 hours were in the same make and model as the accident helicopter; he had also recorded having accumulated 64 hours in the last 90 days and 20 hours, 30 days prior to the accident.

AIRCRAFT INFORMATION

The helicopter was a Bell 47G-5 helicopter, FAA registration N232MC, serial number 7882. It was manufactured and delivered to East Volusia Mosquito Control District, Volusia County, Florida, in 1967. In 1986, the helicopter incurred substantial damage due to an accident, and it remained out of service until 1995, when it was acquired by East Flagler Mosquito Control District. The helicopter received an overhaul/1200-hour inspection, was repaired, and returned to service. According to maintenance records, the helicopter had accumulated 3864.5 hours at the time of its overhaul.

Maintenance records also indicate that the last inspection performed on the aircraft was a 50-hour inspection, conducted on June 28, 2004. Its last 100/600-hour inspection was performed on September 15, 2003. At the time of the accident, the aircraft had accumulated 84.9 hours since the last 100/600-hour inspection and 677.3 hours since the overhaul in 1995.

METEOROLOGICAL INFORMATION

Daylight visual meteorological conditions prevailed at the time of the accident. The Daytona Beach Airport, Daytona Beach, Florida, 1253, surface weather observation was: few clouds at 1,600 feet, scattered clouds at 3,700 feet, a broken cloud layer at 4,400 feet, visibility 10 statute miles, wind from 210 degrees at 6 knots, and the altimeter setting was 29.92 inHg. Daytona Beach, Florida, is located approximately 35 miles south-southeast of the accident site.

WRECKAGE AND IMPACT INFORMATION

The helicopter impacted the ground at 29 degrees 37.81 minutes north latitude and 081 degrees 13.36 minutes west longitude, in a marshy area called Matanzas, just west of the intercoastal waterway, in the city of Palm Coast, in Flagler County, Florida. The accident helicopter lay in approximately 2 feet of water, in a flat area with tall grass, surrounded by trees in the distance, and there was evidence at the site of Abate 4-E insecticide, the chemical carried by the helicopter for its spraying operation.

The fuselage had compressed at the lower front and right side, and the helicopter had come to rest laying on its nose, and slightly on the left side. As it lay, the main mast was horizontal with the transmission and engine was still connected. The short engine to transmission drive shaft had become detached. The two main rotor blades displayed S-type bending. One main rotor blade had impacted the ground with the undersurface of the blade, and the other blade had folded over the helicopter, and was collocated close to the first blade. The helicopter frame aft of the cabin was intact, and displayed little damage. An area where paint had been scrapped off was noted along the bottom of the tail rotor guard.

An examination of the airframe was performed by a representative of Bell Helicopter, under NTSB oversight. The fuselage and cockpit exhibited numerous structural tube fractures and bends. The instrument panel sustained major damage. During the course of the control continuity checks, the cyclic, collective, and anti-torque control systems did not move freely. The pilot's collective stick had fractured consistent with overload forces near the base, and additional control tube fractures were present in the cyclic and collective pitch control systems, and they were consistent with overload forces. Some slight movement was observed at the tail rotor cable quadrant underneath the cockpit when the pedals were manipulated by hand, but the area had been compressed by impact forces. The throttle was observed in the full on position. The fuel valve knob in the cockpit was observed in the on position.

Free rotational movement was present in the main transmission when the mast was rotated manually by the stabilizer bar. Rotational movement was also noted at the fan drive pulley, tail rotor output coupling, and DC generator. A stub pertaining to the forward tail rotor driveshaft section was found in the tail rotor driveshaft output from the main transmission and it had fractured consistent with torsional overload. The tail rotor driveshaft assembly on the tailboom was intact to the universal joint at the aft end of the tailboom. All hanger bearings on the tailboom rotated freely when manipulated by hand. At the driveshaft section at the aft end of the tailboom, one of the universal joint lugs exhibited two fractures on either side of a bore consistent with overload forces. The bottom lug attachment point for the tail rotor guard at the aft end of the tailboom was fractured. Both left and right bosses of the tail rotor drive yoke were fractured consistent with overload forces at the aft upper tailboom attachment points. The aft universal lug of the driveshaft section located in the tail rotor drive extension tube was rotated by hand and free movement was present to the tail rotor assembly. Oil was observed in the sight glass of the tail rotor gearbox. The aft section of the tail boom frame, the tail rotor guard fork assembly, the tail rotor drive yoke, and two sections of the tail rotor drive shaft with the universal joint, one of them enclosed in a section of the tail rotor drive tube assembly, were retained and shipped to the NTSB's Materials Laboratory Division in Washington, D.C., for further analysis.

An examination of the engine was performed by a representative of the engine manufacturer with NTSB oversight. The engine remained partly attached to the airframe. The engine was rotated using a drive tool inserted into the accessory section and internal gear and valve train continuity was confirmed. All six cylinders produced compression. A lighted borescope was used to examine the top end components and no precrash anomalies were noted. The magnetos, spark plugs, carburetor, oil screen and gascolator were individually examined, and no evidence of preimpact mechanical failure or malfunction was identified. Blue color fuel was found in the carburetor.

MEDICAL AND PATHOLOGICAL INFORMATION

On August 5, 2004, a postmortem examination of the accident pilot was performed by the District 23 Medical Examiner's Office, St. Augustine, Florida. The cause of death was attributed to traumatic injuries. No findings which could be considered causal were reported.

Toxicological analysis of specimens of the pilot was performed at the FAA Toxicology and Accident Research Laboratory, Oklahoma City, Oklahoma. Samples were tested for carbon monoxide, cyanide, ethanol, volatiles, and drugs. None were found to be present.

TESTS AND RESEARCH

The NTSB's Materials Laboratory, Washington, D.C., conducted metallurgical examinations of the aft section of the tail boom frame, a piece of the tail rotor guard, the tail rotor drive yoke, and two sections of the tail rotor drive shaft with the universal joint. The section of the tail rotor drive shaft aft of the universal joint was enclosed in a section of the tail rotor drive tube assembly with the drive shaft bearings.

The examination revealed that the forward lugs on the tail rotor drive yoke were fractured. The fracture surfaces were matte gray and rough, consistent with overstress fractures. The brace assembly for the tail rotor drive yoke housing presented evidence consistent with buckling. The bottom lug at the aft section of the tail boom frame where the tail rotor drive yoke housing brace assembly attaches was fractured and deformed adjacent to the fracture, consistent with a tensile overstress fracture.

Examination of the two sections of the tail rotor drive shaft revealed that three spline teeth at the forward end of the section forward of the universal joint were fractured. The fractures had uniform features and were at locations consistent with overstress fractures. The section of the tail rotor drive shaft aft of the universal joint rotated freely within the tail rotor drive tube assembly, but the axis of rotation of the universal joint was not aligned with the axis of the tail rotor drive tube assembly.

Examination of the universal joint revealed that one lug of the universal joint housing was fractured. Damage was observed on both sides of each clevis corresponding to contact with the adjacent lug. Rubbing marks corresponding to contact with the end of each clevis lug were observed on each clevis. Two of the bearing outer race retaining screws were fractured. The fracture surfaces had relatively rough features consistent with tensile overstress fractures, and were mostly covered with uniformly distributed orange to dark red oxides, consistent with postfracture oxidation. Two bearing outer races and rolling elements were missing, one bearing outer race was displaced outward, and one was not flush with the housing lug outer surface. Relatively heavy marks corresponding to contact with the rolling elements were observed on the loaded side of the bearing journals on the universal cross member. On the unloaded side, lighter marks corresponding to multiple bearing contact locations were observed. Some pitting was observed in one of the journals, and another journal had multiple rolling element contact marks at different axial angles.

The same components with the addition of the 90-degree gearbox, the 90-degree gearbox shaft, the tail rotor hub yoke, and the tail rotor blades were analyzed at the Bell Helicopter's Field Investigations Laboratory.

Examination of the aft section of the tailboom revealed that the bottom lug was fractured from overload, with the lughole elongated in an up and aft direction. A section of the lug remained in the tail rotor drive yoke housing brace. The brace assembly was fractured near where it attaches to the yoke, and mechanical damage from impact could be seen where the fracture occurred. The impact and the fracture direction were consistent with the tail rotor drive yoke, tube and gearbox pivoting up and forward. Both lugs on the forward end of the tail rotor drive yoke were fractured from overload. The tops of the lugs showed evidence of impact damage from the yoke and drive tube pivoting up and forward around the two lugs and contacting the top side of the tailboom near the attachment point.

Examination of the universal joint revealed that one of the housing lugs was fractured from overload. There was evidence that the opposite universal joint housing had made contact with this housing from misalignment during an up and forward motion of the combined tail rotor drive assembly. The universal housing lugs were also mechanically damaged and the forks opened. Two sets of bearings were missing. The bearing journals on the universal cross member had areas of mechanical damage (brinelling). The journals also exhibited wear (false brinelling) from contact and relative motion with the bearings. One of the journals had false brinelling marks that were straight and also at an angle.

The tail rotor hub and blades were rotated and the gearbox was found to have continuity through to the drive shaft. The pitch change mechanism was rotated and found to have continuity to the pitch links and blades. One rotor blade was twisted out (away from the drive assembly), and presented green and orange paint transfer along the leading edge and chordwise along the blade in the direction of rotation. It also contained dry mud on the outboard end. The mud was not smeared on and not in the direction of rotation. The other blade was bent out (away from the drive assembly), and presented scuffmarks and green paint transfer in the direction of rotation on the inside (toward drive assembly).

Witnesses reported two tail strikes with the aircraft prior to the accident flight. One witness reported seeing the helicopter hit the tail on the ground during landing, earlier on the day of the accident. Another witness reported seeing the tail boom come in contact with the ground during landing a day earlier. The site where the helicopter had reportedly hit its tail on the day prior to the accident was examined on August 9, 2004. A rounded impression was observed in a sodden area that was consistent with the size and shape of the helicopter's tail rotor guard.

ADDITIONAL INFORMATION

On August 4, 2004, the NTSB released the wreckage of N232MC to Mr. Joseph Cash, Director of East Flagler Mosquito Control District. The NTSB retained a Bell 47-5 maintenance manual and parts from the aft tail boom, tail rotor drive shaft, and tail rotor drive shaft u-joint for further examination. All parts retained by the NTSB were returned to Mr. Cash on September 23, 2004.

NTSB Probable Cause

The pilot's continued flights and inadequate inspections after repeated tail rotor guard ground strikes due to improper flaring, which resulted in an in-flight failure of tail rotor drive shaft components, a loss of control, and the helicopter crash.