SEA07FA014

On-speed failure of the second stage turbine wheel as the result of engine oil starvation. The lack of maintenance oversight was a contributing factor.

While conducting EMS operations the helicopter sustained substantial damage after a loss of engine power, autorotation, and forced landing. The pilot reported hearing a loud bang, followed by the engine spooling down. The helicopter collided with a chain link fence during the forced landing sequence. Postaccident inspection of the engine revealed an uncontained second stage turbine wheel burst (on-speed) as a result of oil starvation and subsequent bearing failure. During the onsite examination, fresh oil residue was noted along the right side of the helicopter's fuselage, tail boom assembly and leading edges of the tail rotor blades. Oil wetting and staining was also observed on the concrete hangar apron, and a trail of fresh oil extended from apron to the helipad where the helicopter departed. Additionally, onsite investigators noted that the oil pressure transducer line coupling B-nut (near the foreword bulkhead) was found two flats loose, and four complete rotations from complete separation. Evidence of oil loss, sooting and localized fire damage was observed in the area of the fitting union. The accident flight was the helicopter's first flight following the completion of a maintenance action item in the general area of the aforementioned fitting. Following the maintenance action, an engine run (ground) and post run inspection was completed by a line pilot. No discrepancies were noted and the helicopter was returned to service. The mechanic who performed the maintenance action was not present during the post run inspection.

HISTORY OF FLIGHT On November 2, 2006, at 2055 mountain standard time, a Bell 407 helicopter, N407KH, sustained substantial damage during a forced landing, subsequent to a loss of engine power (uncontained failure), shortly after departure from the Kalispell Regional Medical Center, Kalispell, Montana. The helicopter was operated as a visual flight rules (VFR) emergency medical services (EMS) positioning flight under Title 14, CFR Part 91. Of the three occupants aboard, the certificated commercial helicopter pilot and two medical crewmembers were not injured. The helicopter was owned and operated by Kalispell Regional Medical Center, Kalispell, Montana. Dark night visual meteorological conditions prevailed, and company VFR flight following procedures were in effect. The flight originated about 2051 from the hospital's helipad, and was en route to Bigfork, Montana (approximately 12 miles east-southeast). The helicopter sustained substantial damage to the tail boom assembly during the landing sequence. During a telephone conversation with the National Transportation Safety Board investigator-in-charge (November 2), and in a subsequent written statement, the pilot of the accident helicopter reported that approximately 1 minute after takeoff (during the initial climb) from the hospital's helipad, the flight paramedic, who was seated in the left front seat, informed him (the pilot) that the "ENG [engine] CHIP" light on the caution light panel had just illuminated. The pilot stated that after confirming the caution light "I immediately flipped my goggles [the pilot was wearing night vision goggles- NVG's] up and turned the helicopter around and headed back to hospital because it was the closest available pad and it was illuminated." The pilot stated that the engine started making "weird growling noises" and began to "surge" as he turned a 1/4-mile final for the helipad. The pilot reported that the growling noise and surging was followed by a loud "bang" which emanated from the rear of the helicopter. The pilot stated that he lowered the collective and entered an autorotation. The helicopter touched down at the perimeter of the intended helipad and collided with a chain link fence. The helicopter slid approximately 25 feet before coming to rest. The pilot completed an emergency "shutdown," and he and the two crewmembers exited the helicopter without injuries. After exiting the helicopter, the pilot and staff from the hospital's emergency department (ED) extinguished a small fire in the helicopters engine bay. The purpose of the flight was to pick-up a medical patient in Bigfork and return to the departure hospital. SURVIVAL ASPECTS The pilot, seated in the right front seat, the flight paramedic, seated in the left front seat and the flight nurse, seated in the right rear forward facing seat, were not injured. PERSONNEL INFORMATION The pilot-in-command held a commercial pilot certificate with airplane single-engine land, helicopter-rotorcraft and helicopter instrument ratings. The pilot's most recent FAA second-class medical certificate was issued on October 10, 2006. The medical certificate carried no limitations or waivers. According to the Pilot/Operator accident report (Form 6120.1/2), completed by the operator, the pilot's total time was 3,000 hours; 2,430 hours (PIC) rotorcraft and 500 hours total PIC time in Bell 407's. The report indicated that the pilot had flown 43 hours in the 90-day period preceding the accident, of which 31 hours were in a Bell 407. The pilot completed a 5-day factory ground and flight training course for the Bell 407 at the Bell Helicopter Training Academy in August of 2006. On March 31, 2006, the pilot completed initial training and testing requirements prescribed by FAR 135.293 and 135.295. The pilot began his employment as a pilot with Kalispell Regional Medical Center in March of 2006. AIRCRAFT INFORMATION The helicopter, a Bell 407, serial number 53395, was manufactured in 1999. The single-engine helicopter was powered by a Rolls-Royce model 250-C47B turbo shaft engine (serial number CAE 847433). The helicopter was configured and equipped for EMS operations. The helicopter was maintained in accordance with an Approved Airworthiness Inspection Program (AAIP) on a continuous basis. The helicopter's last inspection, a phase 3 inspection, in accordance with the AAIP, was completed on September 15, 2006. The helicopter's total time at inspection was 3,138 hours. At the time of the accident, the helicopter's total time was 3,213.9 hours. According to the operator, the helicopter was removed from service on the day of the accident to facilitate the completion of Bell Helicopter Technical Bulletin (TB) 407-05-63 "Rotor Brake Modification Kit 407-704-022-101, Installation Of." The TB outlines the procedures and parameters for replacement/modification of the rotor brake assembly. According to the manufacture, installation of the brake modification kit will minimize wear associated with vibration. The Hobbs time at the completion of the maintenance action was 3,213.8. At the completion of the aforementioned maintenance actions, an engine run (ground) was completed. A post run-up inspection, completed by the pilot, noted no discrepancies or anomalies. Night visual meteorological conditions prevailed at the time of the engine run. The mechanic who performed the maintenance was not present during the run-up or subsequent post run inspection. The engine cowlings were not opened during the post run inspection. At the completion of the maintenance run, the helicopter was moved to a hangar where the post maintenance run inspection was completed and then returned to service. The maintenance action began about 1100 and was completed about 1830 local. There were no open logbook maintenance discrepancies concerning the helicopter at the time of the accident. METEOROLOGICAL INFORMATION The closest weather observation recourse to the accident site was an Automated Surface Observing System (ASOS) located at Glacier Park International Airport (KGPI), 6 nautical miles northeast of the accident location at an elevation of 2,977 feet above mean sea level (msl). The 2053 METAR (Aviation Routine Weather Report) observation was, in part, prevailing visibility 2 statute miles in mist and light snow, overcast skies at 1,700 feet, temperature -2 degrees C, dew point -3 degrees C. WRECKAGE AND IMPACT INFORMATION Representatives from the Helena, Montana, Flight Standards District Office (FSDO), Bell Helicopter and Rolls-Royce conducted the initial on scene portion of the investigation, which commenced on November 3, and reported the following finding: The fuselage was intact and minimal damage was noted to the main and aft cabin. Damage was noted to the tail rotor driveshaft, driveshaft housing and horizontal stabilizer. A section of the tail rotor drive shaft was located on the roof of the hospital approximately 225 feet from the point of touchdown. All four main rotor blades were intact, however, impact related damage (near the blade tips) was observed to the leading edges of the main rotor blades. The tail rotor gearbox and associated tail rotor blades were intact. Fresh oil residue was noted along the right side of the helicopter's fuselage below the engine bay. The oil residue was more prominent near the forward section of the engine bay. Fresh oil residue was also noted along the tail boom assembly and on the leading edges of the tail rotor blades. The onsite investigative team also reported that oil wetting and staining was observed on the concrete hangar apron, and a trail of fresh oil extended from apron to the helipad where the helicopter departed. Oil was also noted on the hangar door and several locations around the pad. Extensive tearing type damage was noted to the upper engine cowling.