NTSB Factual Report

On August 20, 1998, at 2114 central daylight time (All times central daylight time), a Bell 222, N30SV, operated by Rocky Mountain Holdings, was destroyed as a result of an in-flight breakup during cruise descent. The pilot, flight nurse, and flight paramedic were fatally injured. The 14 CFR Part 91 flight had departed from the Sioux Valley Hospital, Sioux Falls, South Dakota, and was en route to the Spencer Municipal Hospital, Spencer, Iowa, for a patient transfer. Visual meteorological conditions prevailed and a company VFR flight plan had been filed.

The Sioux Valley Hospital Communications Center's Transport Request form indicated that they had received a call from the Spencer Municipal Hospital for a helicopter transport at 2027. The transport log indicated that the pilot was notified at 2027 and that the pilot checked the weather. He confirmed that the weather was acceptable for a VFR night flight at 2031. The transport log indicated that the helicopter departed at 2039. The distance to the Spencer Municipal Hospital was 71 miles. The ETE was 33 minutes. The helicopter had 1:45 hours fuel on board.

The transport log indicated that the pilot made three position reports during the flight. At 2052, the helicopter had an ETA of 22 minutes. At 2101, the helicopter had an ETA of 13 minutes. At 2109, the helicopter ha an ETA of 5 minutes. The pilot did not indicate there was any anomaly concerning the flight when he provided the position reports.

Radar data indicated the helicopter maintained a direct course to Spencer, Iowa. The helicopter maintained an altitude between 2,500 to 3,000 feet msl at an airspeed of approximately 130 knots. The last radar contact was at 2114:18. It indicated the helicopter was 1.5 miles from the Spencer Municipal Airport on about the 290 radial at 2,300 feet msl. The elevation at the Spencer Municipal Airport is 1,339 feet msl. The last radar contact indicated the helicopter was about 961 feet above ground level.

The helicopter impacted the ground approximately 0.8 miles west of the Spencer Municipal Airport.

Personnel Information

The pilot was a commercially rated helicopter pilot with an instrument rating in helicopters. He also held a private pilot airplane single engine land rating. He held a Second Class Medical Certificate. He had a total of about 3,918 hours of flight time. 3,872 hours were in helicopters. 597 hours were in the Bell 222SP helicopter. He had completed recurrent ground and flight training in the Bell 222SP helicopter on April 26, 1998, and had successfully completed a Part 135 check ride on April 27, 1998.

The pilot had eight years experience operating from the Sioux Valley Hospital. The flight paramedic had one year eight months experience in the hospital's flight department. The flight nurse had four months experience in the hospital's flight department.

Aircraft Information

The helicopter was a twin engine Bell 222SP, serial number 47044. In the medical configuration, the helicopter had four seats which included the patient stretcher. The gross weight was 7,850 pounds. The engines were 650 shaft horsepower Allison 250-C30G engines. The helicopter was on an Approved Airworthiness Inspection Program (AAIP). The helicopter had flown 2.5 hours since the last inspection and had a total of 3,251 hours.

The engine logbooks indicated that the left engine was last inspected on July 16, 1998. The right engine was last inspected on July 17, 1998. The engines' next inspection was due in about another 50 flight hours.

The Sioux Valley Hospital had started operating the helicopter in January 1993. The aircraft had a 738.4 total hours when it was put into operation by the hospital.

The airframe logbook indicated that the helicopter had undergone a "B" inspection on August 17, 1998. The mechanic who signed off the inspection reported that during the performance of the B inspection, he discovered the friction on the swashplate was below the allowable limits. He reported that he and another mechanic performed the necessary work to bring the friction into the proper limits. In order to do the inspection, the mechanics disconnected the swashplate drive links, cyclic links, and pitch links. The mechanic reported that torque wrenches were used when the components were re-attached, although, the mechanic reported he could not specifically recall if the drive link bolts had been checked with a torque wrench. The mechanic reported that after the work was completed, the mechanics inspected each other's work for proper safeties and cotter keys. The mechanic reported that after all the maintenance was performed, the pilot on-duty (who happened to be the accident pilot), examined the preformed maintenance and conducted a ground run. The mechanic reported that the pilot indicated that the helicopter was satisfactory.

The helicopter was not flown on August 17, 1998, but it received two preflight inspections by the on-duty pilots. On August 18, 1998, the helicopter flew a 0.8 hour flight, and had received two preflight inspections by the on-duty pilots.

On August 19, 1998, the mechanic performed maintenance on the helicopter in the morning that included changing the bearings of the cyclic links. The mechanic reported that he changed both bearings of the left cyclic link and the upper bearing of the right cyclic link. The maintenance to the cyclic links did not require the drive links to be disconnected. The mechanic reported that he entered the logbook entries for the maintenance performed on the emergency locator transmitter and a helipilot computer. The inspection of the logbook indicated that the entry for the maintenance performed on the cyclic links was not entered into the logbook, although a record of the maintenance was listed in the mechanics' maintenance computer.

On August 19, 1998, the aircraft flew a 0.9 hour flight, and it had received a Daily Preflight check by the on-duty mechanic and two pilot preflight checks by the on-duty pilots.

On August 20, 1998, the aircraft received a Daily Preflight by the on-duty mechanic in the morning. The logbook also indicated that the accident pilot, who was scheduled as the night pilot (1900 August 20 through 0700 of August 21), performed a preflight inspection of the helicopter. At 2039, the pilot departed the hospital on the accident flight.

Maintenance records indicated that an overhauled swashplate was installed on the helicopter on July 16, 1997. On August 20, 1998, the time since overhaul was 462.6 hours.

The helicopter departed with 1:45 hours of fuel on board. It had approximately 1:15 hours of fuel on board when it impacted the ground.

Meteorological Conditions

At 2053, weather conditions reported at the Spencer Municipal Airport were VMC. The winds were 260 degrees at 12 knots gusting to 26 knots. Visibility was 10 miles with an 8,500 foot overcast layer. The temperature was 74 degrees Fahrenheit. The dew point was 68 degrees Fahrenheit. The altimeter was 30.26.

At 2153, weather conditions reported at the Spencer Municipal Airport were VFR. The winds were 080 degrees at 15 knots. Visibility was 6 miles with 8,500 foot broken layer. The temperature was 70 degrees Fahrenheit. The dew point was 68 degrees Fahrenheit. The altimeter was 30.20.

Wreckage and Impact Information

The helicopter wreckage was located on a line approximately 0.8 to 1.2 miles west, northwest from the runway intersection at the Spencer Municipal Airport. The direction of travel was approximately 090 degrees.

The majority of the helicopter wreckage landed in two mature bean fields where the beans had grown to about 38 inches in height. On August 21, 1998, aerial searches were conducted to locate the main sections of wreckage. On August 22, 1998, about 45 volunteers searched the bean fields for 2.5 hours to locate additional wreckage. The areas searched were located north and west of the location of the tailboom and tailrotor.

A blue plexi-glass piece and two sections of the tailrotor driveshaft cover were located at the westernmost end of the debris field. Numerous small parts of aircraft wreckage were located in the debris field between the western end of the debris field and the fuselage located at the eastern end of the wreckage path.

The fuselage impacted the bean field approximately 0.5 miles from the initial point of in-flight breakup. The direction of travel of the fuselage after ground impact was about 090 degrees. The longitudinal axis of the aircraft was found heading about 320 degrees.

The left landing gear sponson was located about three feet in front of the initial impact point of the fuselage. The right landing gear sponson separated from the fuselage and was located about 150 feet east of the left sponson. The fuel bladder from the right sponson was found near the right sponson. The fuel bladder had burst and there was evidence of jet fuel having sprayed on the bean plants in the debris area of the fuselage wreckage.

The majority of the fuselage, which included the area from the nose section to the tailboom attachment area, was destroyed by fire. The transmission and engines received fire damage and were found inverted under the right side of the fuselage wreckage.

All engine components were located at the main wreckage site. Both engines had broken off from the airframe mounts, but each engine was found within its respective engine compartment. Both engines and gearboxes were consumed by fire.

The tailrotor driveshaft assembly at the main impact site included the first two sections of the tailrotor driveshaft. The number one tailrotor drive shaft had separated from the transmission during impact. The section between the engine firewalls was consumed by fire. The number two section of tailrotor drive shaft was intact but was bent and crushed.

The right horizontal stabilizer and a section of the tailboom which remained attached to the stabilizer was located about 0.35 miles from the main wreckage on a heading of 290 degrees.

A fiber washer that was part of the "white" drive link/swashplate outer ring pin assembly from the main rotor was found about 0.15 mile west of the tailboom and tailrotor, and about 0.35 miles west of the main wreckage.

The tailboom and attached tailrotor were located about 0.2 miles from the main wreckage on a heading of 270 degrees.

The main rotor and attached blades were located about 0.18 miles from the main wreckage on a heading of 300 degrees.

Examination of the main rotor assembly indicated that the "white" swashplate outer ring pin that attached the white drive link to the rotating swashplate was fractured within the bolt hole of the swashplate. The corresponding pin, nut, washers, and cotter key had separated and were not located. The "red" swashplate outer pin and drive link assembly remained attached to the swashplate.

Medical and Pathological Information

An autopsy was performed on the pilot at the LCM Pathologists, P.C., Sioux Falls, South Dakota.

A Forensic Toxicology Fatal Accident Report was prepared by the FAA Civil Aeromedical Institute. The report concerning the pilot indicated the following results:

Carbon Monoxide: Not performed due to lack of suitable specimen.

No Cyanide detected in blood.

35 (mg/dL, mg/hg) Ethanol detected in muscle.

37 (mg/dL, mg/hg) Ethanol detected in kidney.

19 (mg,dL, mg/hg) Acetaldehyde detected in kidney.

No drugs detected in blood.

The detection of ethanol and acetaldehyde was the result of putrefaction.

Tests and Research

The engine inspection indicated that both engines were rotating at the time of impact. The No. 2 engine had evidence of fused aluminum deposits on the 1st stage nozzle guide vanes.

The swashplate assembly, main rotor hub, and the main transmission and mast assembly were examined at the Bell Helicopter Textron Metallurgical Laboratory in Fort Worth, Texas, under the supervision of the National Transportation Safety Board.

The main rotor mast, main rotor trunnion, rotating controls drive plate and main rotor controls drive hub were inspected to determine that they were properly indexed relative to the master splines and to each other. The components were found to meet the engineering drawing requirements for indexing relative to the master splines and to each other.

The main rotor hub assembly was tested to determine the spring rates of the elastomeric bearings. No abnormal spring rates were observed in the test.

The fractures observed in the main rotors controls installation components and transmission case were determined to be the result of overstress fractures.

The examination of the swashplate outer ring pins revealed a bending fatigue fracture occurred in the "white" (S/N TI 15) pin. The fatigue cracking originated in the undercut fillet radius adjacent to the head of the pin. The pin was found to meet the engineering drawing requirements for hardness and the remaining portion of the fillet radius was within the engineering drawing limits.

An examination on the S/N TI 15 pin's fracture surface with an optical and a scanning electron revealed no discrepancies in the fatigue origin area. The fracture surface had dark corrosion products in it. A fatigue striation count was made from replicas of the fracture surface that indicated the pin had 196,000 load cycles that caused fatigue growth. It was not known how many load cycles did not cause fatigue growth.

The swashplate outer ring assembly, part number 222-010-404-113, S/N TI 6, was inspected. The holes where the fractured "white" pin and the "red" pin had been located were measured at four locations. The fractured "white" pin hole was 0.0015 to 0.0051 inch above the engineering drawing requirement of 0.6230 to 0,6235 inch. The "red" pin hole was 0.0007 to 0.0031 inch above the engineering drawing requirement. Both holes had visual evidence of wear. Wear also occurred where the pin corners contacted the inner ring. The heaviest wear occurred as a result of a counterclockwise (as viewed looking inboard) force on the pin in the hole. The TI 6 swashplate had been in service for 462 flight hours.

The engineering drawings required that the swashplate outer ring pins diameters be within 0.6240 to 0.6250 inch. The white pin from the TI 6 swashplate was S/N TI 15. It was not possible to measure the diameter of pin TI 15 since it had not been located at the accident site. The red pin from the TI 6 swashplate was S/N TI 37. Various measurements taken of the TI 37 pin indicated diameters of 0.6243. 0.6236, 0.6238, 0.6234, and 0.6229 inch.

Examination of the swashplate outer ring assembly revealed that the flats of the swashplate pin heads were causing wear on the inside surface of the swashplate ring. The wear pattern indicated the swashplate pin was turning in a counterclockwise direction. No wear or movement of the pin is permitted by the maintenance manual.

The swashplate, the white drive link and trunion bearing, the fractured trunion bolt, and the exemplar red drive link and trunion assembly were examined for verification purposes at the National Transportation Safety Board's Metallurgical Laboratory.

Additional Information

The definition of interference fit according to the Dictionary of Aeronautical Terms, Aviation Supplies and Academics, ed. Dale Crane, is, "A type of fit used when assembling certain mechanical devices. To create an interference fit, a hole is made smaller than the part that fits into it. The material containing the hole is heated to expand the hole, and the object to fit in the hole is chilled to shrink it. The parts are easily assembled when one is hot and the other is cold, but when they reach the same temperature, the fit is so tight they will not loosen in service."

The swashplate outer ring assembly that had been replaced during overhaul on July 16, 1997, was obtained from the maintenance facility that overhauled the swashplate. The facility's maintenance records indicated that the swashplate had been sent in for overhaul because of loose swashplate outer ring pins. A technician from the maintenance facility report

NTSB Probable Cause

The below standard (loose) fit of the 'white' swashplate outer ring pin resulting in fatigue and subsequent separation of the pin, and ultimately the in-flight breakup of the rotorcraft. A factor was the manufacturer's dissemination of the pin which did not meet dimensional standards.