History of Flight
On August 31, 2008, at approximately 1320 eastern daylight time, a Bell 206L-1 helicopter, registration N37AE, operated by Air Evac EMS Inc., was destroyed during an in-flight collision with terrain and subsequent post-impact fire near Greensburg, Indiana. The flight was conducted under 14 Code of Federal Regulations Part 91 without a flight plan in visual meteorological conditions. 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 in Rushville, Indiana.
The crew had attended a local fundraising event for the Burney fire station in a community support role, with no patient transport activity associated with the flight. The return flight lifted off at 1317. Witnesses reported that the helicopter cleared a set of high-tension power lines east of the fire station before components separated from the aircraft, after which it descended and impacted the ground. Local authorities from the Burney fire station responded within approximately 2 minutes. The helicopter came to rest about 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, including instrument ratings for both. He was issued a Second-Class Airman medical certificate without limitations on April 22, 2008. The pilot was hired by the operator on June 14, 2006, and completed his most recent Part 135 checkride on June 10, 2008. He had accumulated approximately 5,493 hours total flight time, with about 5,176 hours in helicopters and 1,915 hours in the same make and model as the accident aircraft. In the 90-day and 30-day periods prior to the accident, he had flown about 38 hours and 9 hours, respectively, and about 419 hours during his tenure with the company. The pilot had been scheduled for 12-hour shifts from 0800 to 2000 for a 7-day period starting August 25, with the accident occurring on the 7th day. He had flown 3.1 hours during the preceding 6 days, with 1.5 hours flown the previous day, and was off-duty for the 4 days prior to the assignment.
Aircraft Information
The accident helicopter, N37AE, was a 1979 Bell Helicopter Textron 206L-1, serial number 45230, powered by a Rolls-Royce/Allison Model 250-C30P turbo-shaft engine. It was owned and operated by Air Evac EMS Inc. in an air medical transport role. The helicopter had accumulated 26,250 hours total flight time as of the accident date, with the engine accumulating 11,554 hours and 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, consisting of an Event 1 and a 200-Hour procedure. Maintenance records from that date noted a discrepancy: "While on approach heard (and) felt low rumble (and) vibration from rear of aircraft." However, subsequent inspection did not reveal any anomalies, and a ground run and flight check could not duplicate the issue. The main rotor blades (part number 206-015-001-115, serial numbers A-5165 and A-5168) were installed new on March 21, 2005, and had accumulated about 2,808 hours time in service at the time of the accident, with a service life of 3,600 hours. No write-ups related to the main rotor blades were found in discrepancy records from January 1, 2008, through the accident date.
Meteorological Information
The closest weather reporting facility was Columbus Municipal Airport (BAK), about 16 miles west-southwest of the accident site, equipped with an Automated Weather Observing System (AWOS). At 1250, conditions were: winds from 090 degrees at 9 knots; visibility 10 miles; clear skies; temperature 30 degrees Celsius; altimeter 30.18 inches of mercury. At 1350, conditions were: winds from 080 degrees at 10 knots; visibility 10 miles; few clouds at 4,000 feet; temperature 30 degrees Celsius; altimeter 30.16 inches of mercury.
Wreckage and Impact Information
The main wreckage, consisting of the fuselage, engine, tail boom, and landing skids, was located in a cornfield. The fuselage was consumed by post-impact fire and came to rest nearly inverted on an approximate 317-degree magnetic heading. The tail boom and landing skids separated and were found about 10 feet south and 10 feet southwest of the fuselage, respectively. The main rotor blade/hub assembly separated at the rotor mast and was found approximately 220 yards west-southwest of the main wreckage. The cockpit and cabin were destroyed by impact and fire. Flight controls were damaged consistent with impact forces. The engine remained secured to the airframe, and the transmission separated, found about 194 yards northeast. Post-accident examinations of the engine and transmission revealed no pre-impact anomalies. The main rotor blades remained attached to the hub; one blade was intact, the other fractured into three sections. The outboard section (about 8 feet) was found 147 yards west-northwest, and the mid-blade section (about 3 feet) was found 40 yards west-southwest. The main rotor mast failed near the lower surface of the hub, bent in the direction of the failed blade, with indentations matching teetering stops. The fracture surface exhibited 45-degree shear planes and a dull appearance consistent with overload failure. The tail boom separated about 12 inches aft of the fuselage attachment, with a linear indentation on the left side. The left horizontal stabilizer separated near the root, consistent with a main rotor blade strike, found about 212 yards south of the main wreckage.
Medical and Pathological Information
An autopsy of the pilot was performed by the Marion County Coroner's Office, Indianapolis, Indiana, on September 2, 2008. The cause of death was attributed to multiple blunt force trauma. A Forensic Toxicology Fatal Accident Report prepared by the FAA Civil Aeromedical Institute returned negative results for all substances tested.
Tests and Research
The NTSB materials laboratory conducted a metallurgical examination of the failed main rotor blade. The blade, part number 206-015-001-115, serial number A5165, exhibited a complete fracture about 96 inches from the tip (blade station 126.5) and a second section fractured about 134 inches from the tip (blade station 88.5). Examination of the fracture surfaces revealed ratchet marks and fine elliptical clamshell marks typical of fatigue cracking, emanating from the inner face of the spar at the transition radius between the leading edge and the upper wall. The fatigue crack propagated upward and encompassed approximately 50 percent of the cross-sectional area of the spar before ultimate failure. The spar surface showed no evidence of corrosion or previous mechanical damage, but fine lengthwise extrusion marks were present. The origin of the fatigue crack coincided with a large void in the adhesive between the inside surface of the spar and a lead weight, measuring approximately 0.4 by 0.1 inches in cross-section and about 9.2 inches in total length. The spar surface was clean with no adhesive material at the fracture location. Further investigation by the manufacturer determined that residual stresses in the spar from manufacturing, combined with excessive voids between the spar and the lead weight, can lead to fatigue failure.
Additional Information
As a result of the investigation, the manufacturer released Alert Service Bulletin 206L-09-159 (Revision A), informing operators that a combination of residual stresses and excessive voids may lead to fatigue cracking. The bulletin listed affected main rotor blades and recommended recurring inspections, including a wipe check and visual inspection for cracks or x-ray inspection to identify voids. If no excessive voids were found, no further inspection was recommended; if excessive voids were identified, the recurring visual inspection was recommended for the life of the blade. Additionally, the manufacturer determined that several main rotor blades had been manufactured with an oversized spar spacer, leading to Alert Service Bulletin 206L-09-163. This bulletin notified operators that an oversized spacer combined with larger-than-acceptable voids between blade stations 100 and 145 may cause fatigue cracking. For blades with an oversized spacer, the bulletin recommended reducing the service life from 3,600 to 2,300 flight hours and, for blades with over 1,200 flight hours, recurring inspections.
Other Information
Weather conditions at the accident site were clear with 10 miles visibility and daylight. The helicopter was equipped with a terrain awareness warning system (TAWS) and a radar altimeter. The flight was tracked by a flight-following program and received dispatch services; a formal flight risk assessment was performed prior to departure. The NTSB had previously issued safety recommendations regarding EMS operations, including Recommendations A-06-12 through A-06-15, which were placed on the NTSB's "Most Wanted List of Safety Improvements" in October 2008.