CHI08FA269

The in-flight separation of a main rotor blade due to a fatigue failure of the blade spar, rendering the helicopter uncontrollable, and the manufacturer's production of main rotor blades with latent manufacturing defects, which precipitated the fatigue failure of the blade spar.

The emergency medical services crew had attended a local fundraising event and was returning to the helicopter/crew base when the accident occurred. Witnesses reported that the helicopter made a normal departure. They subsequently reported seeing components separate from the helicopter before it descended and impacted the ground. The helicopter came to rest in a corn field approximately 1.2 miles from the departure point. A postaccident examination of the helicopter revealed that an 8-foot section of one of the main rotor blades separated in-flight rendering the helicopter uncontrollable. Metallurgical examination determined that the blade failed as a result of fatigue cracking. The origin of the fatigue crack coincided with a large void between the blade spar and an internal lead weight. Further investigation determined that the presence of residual stresses in the spar from the manufacturing process, in combination with excessive voids between the spar and the lead weight, likely resulted in the fatigue failure of the blade. The manufacturer issued an alert service bulletin that identified main rotor blades that may have been affected by the combination of residual stresses and excessive voids between the spar and the lead weight. The service bulletin also called for supplemental inspections in order to maintain the continued airworthiness of the affected blades.

HISTORY OF FLIGHT On August 31, 2008, about 1320 eastern daylight time, a Bell 206L-1 helicopter, N37AE, operated by Air Evac EMS Inc., was destroyed during an in-flight collision with terrain and post impact fire near Greensburg, Indiana. The flight was being conducted under 14 Code of Federal Regulations Part 91 without a flight plan. Visual meteorological conditions prevailed. The pilot, flight nurse, and paramedic sustained fatal injuries. The accident flight departed at 1317 from Burney, Indiana, with the intention of returning to the aircraft's base located in Rushville, Indiana. The crew had attended a local fund raising event for the Burney fire station in a community support role. No patient transport activity was associated with the flight to the fire station, or with the accident flight. The crew had arrived at the event about 1150 that morning. The return flight lifted off at 1317. Witnesses reported that the helicopter appeared to depart the fire station without difficulty. One witness recalled seeing the helicopter clear a set of high-tension power lines east of the fire station. Witnesses stated that they subsequently saw components separate from the helicopter before it descended and impacted the ground. Local authorities from the fire station in Burney responded upon witnessing the accident. One firefighter estimated that they were on-scene within 2 minutes. The helicopter came to rest approximately 1.2 miles north-northeast of the departure point in a cornfield. PERSONNEL INFORMATION The accident pilot, age 43, held a Commercial Pilot certificate with rotorcraft helicopter and single-engine land airplane ratings. His certificate also included an instrument rating for both helicopters and airplanes. The airplane rating was limited to private pilot privileges. He was issued a Second-Class Airman medical certificate without limitations or waivers on April 22, 2008. The accident pilot was hired by the operator on June 14, 2006. His most recent Part 135 checkride was completed on June 10, 2008. The pilot had acquired approximately 5,493 hours total flight time. Of that flight time, about 5,176 hours were in helicopters and 1,915 hours were in the same make and model as the accident aircraft. He had accumulated about 38 hours and 9 hours in the 90-day and 30-day periods prior to the accident, respectively. He had acquired about 419 hours during his tenure with the company. According to the operator's duty logs, the accident pilot had been scheduled for 12-hour shifts from 0800 until 2000, for a 7-day period beginning on August 25th. The accident occurred on the 7th day of the rotation. He had flown 3.1 hours during that 6-day period, with 1.5 hours flown the previous day. He was off-duty for the 4 days prior to that 7-day assignment. AIRCRAFT INFORMATION The accident helicopter, N37AE, was a 1979 Bell Helicopter Textron 206L-1, serial number 45230. It was powered by a Rolls-Royce/Allison Model 250-C30P turbo-shaft engine, serial number CAE-895470. The helicopter was certificated under FAA type certificate H2SW. It was owned and operated by Air Evac EMS Inc in an air medical transport role. According to the operator's maintenance records, the accident helicopter had accumulated 26,250 hours total flight time as of the day of the accident. The engine had accumulated 11,554 hours, which was comprised of 27,403 start cycles. The helicopter was maintained under an FAA Approved Aircraft Inspection Program (AAIP). The most recent AAIP phase inspection was completed on August 21, 2008. The inspection consisted of an Event 1 and a 200-Hour procedure as outlined in the AAIP. The airframe time was recorded as 26,243.9 hours, at the time of that inspection. Prior to that, an Event 4 inspection procedure had been accomplished on August 12, 2008, at 26,232.5 hours airframe time. The records contained a maintenance discrepancy that stated: "While on approach heard (and) felt low rumble (and) vibration from rear of aircraft." The entry was dated August 21, 2008, the same day as the Event 1 and 200-Hour progressive phase inspection. The aircraft time noted was 1.3 hours after the inspection. The resulting maintenance inspection did not reveal any anomalies. A ground run and flight check could not duplicate the write-up, nor did they identify any discrepancies. There was no mention of a similar discrepancy in the maintenance records subsequent to that event. Maintenance records indicated that the main rotor blades (part number 206-015-001-115, serial numbers A-5165 and A-5168) were installed on the accident helicopter on March 21, 2005. Both blades were new at that time. The aircraft flight time was 23,442 hours at installation. At the time of the accident, the blades had accumulated about 2,808 hours time in service. The blade service life was 3,600 hours. A review of aircraft discrepancy and maintenance records provided by the operator from January 1, 2008, through the date of the accident, did not reveal any write-ups related to the main rotor blades. The accident helicopter was based at Rushville, Indiana, which was located about 18 miles north of the accident site. METEOROLOGICAL INFORMATION The closest weather reporting facility to the accident site was Columbus Municipal Airport (BAK), which was located approximately 16 miles west-southwest of the accident site. The airport was equipped with an Automated Weather Observing System (AWOS). At 1250 the BAK AWOS recorded conditions as: Winds from 090 degrees at 9 knots; 10 miles visibility; clear skies; temperature 30 degrees Celsius; and altimeter 30.18 inches of mercury. The dew point was not available. At 1350, the BAK AWOS recorded conditions as: Winds from 080 degrees at 10 knots; 10 miles visibility; few clouds at 4,000 feet above ground level; temperature 30 degrees Celsius; and altimeter 30.16 inches of mercury. The dew point was not available. WRECKAGE AND IMPACT INFORMATION The accident site was located in a cornfield approximately 1.2 miles north-northeast of the departure point. The main wreckage consisted of the fuselage, engine, tail boom, and landing skids. The fuselage was consumed by a post impact fire. The tail boom and landing skids separated from the fuselage. The tail boom was located about 10 feet south of the fuselage, and the skids were located about 10 feet southwest of the fuselage. The main rotor blade/hub assembly separated at the rotor mast and came to rest approximately 220 yards west-southwest of the main wreckage. The fuselage came to rest nearly inverted. It was oriented on an approximate 317-degree magnetic heading. The cockpit and cabin areas were destroyed by impact forces and the post impact fire. The flight controls were damaged consistent with impact forces. The engine assembly remained secured to the airframe. The transmission separated from the airframe and was located about 194 yards northeast of the main wreckage. Post accident examinations of the engine and transmission did not reveal any anomalies consistent with a pre impact failure. The main rotor blades remained attached to the hub. One blade was intact. The other blade was fractured into three sections, with the inboard blade section remaining attached to the hub. The two separated blade sections were recovered at the accident site. The outboard section, about 8 feet in length, was recovered approximately 147 yards west-northwest of the main wreckage. The mid-blade section, about 3 feet in length, was recovered approximately 40 yards west-southwest of the main wreckage. The main rotor hub and attached rotor blades had separated from the aircraft. The main rotor mast failed near the lower surface of the hub. The mast was bent in the direction of the failed blade immediately above the point of failure. The mast exhibited indentations matching the teetering stops on the hub. The fracture surface of the main rotor mast exhibited