Accident Overview
On January 7, 2008, about 1845 eastern standard time, a Bell 407, registration N801DS, was substantially damaged during a forced landing near DeLand, Florida. The commercial pilot and a paramedic on board were not injured. Visual meteorological conditions prevailed, and a company flight plan was filed for the positioning flight, which departed DeLand Municipal Airport (DED) at 1831, destined for an off-airport site in DeLand. The flight was conducted under 14 Code of Federal Regulations Part 91.
Pilot Account
According to the pilot, while en route to pick up an injured pedestrian for an emergency medical service flight (Part 135), the helicopter was cruising at 120 knots and 700 feet above ground. About two city blocks from the intended destination, the pilot heard a loud "bang," and the helicopter yawed left about 30 degrees. He also heard "squealing or scratching" metallic sounds, the sound of the Full Authority Digital Engine Control (FADEC) warning horn, and observed five warning lights illuminate. About two seconds after the initial bang, the low rotor rpm warning horn sounded. The pilot initiated an autorotation and maintained airspeed at 60 knots.
The pilot identified a roadway under construction for the forced landing. As the helicopter touched down, he maneuvered left to avoid construction equipment and "flared a little too high." The helicopter landed firmly, but not hard, in a level attitude and slid along the ground. During the slide, the tail raised, and the pilot applied aft cyclic. He believed the main rotor blade may have contacted the vertical stabilizer. After coming to rest, the pilot and paramedic exited, observed a fire in the engine compartment, and attempted to extinguish it with the onboard fire extinguisher. The pilot did not recall smelling smoke during the flight.
Witness Account
A witness sitting in a nearby parking lot reported looking up and seeing a "big orange glow [and] then sparks" emanating from the right side of the helicopter before it descended toward the ground.
Post-accident Examination
Examination by Federal Aviation Administration (FAA) inspectors revealed damage to the vertical stabilizer consistent with main rotor blade contact.
Engine Examination
The engine was removed and examined by the manufacturer under FAA supervision. The compressor section (inlet and impeller leading edges) was free from damage and unremarkable. Both N1 and N2 gear trains turned freely and smoothly. Continuity of the N2 was confirmed. Circumferential scoring was noted on the aft face of the pinion gear, consistent with contact between the pinion gear and the power turbine outer shaft forward face during operation. The N2 speed pick up displayed raised metal consistent with contact between the pickup and the number 5 bearing castellated nut. The number 5 bearing oil nozzle was scored, consistent with contact between the nozzle and the forward section of the power turbine rotor.
Turbine section components underwent metallurgical examination. A single third-stage turbine wheel blade had cracked, exhibiting signatures consistent with fatigue, from the trailing edge area toward the leading edge for about 0.5 inches, before separating in overload. Damage to the first-stage turbine wheel was consistent with an over-speed burst, resulting from a fracture through the turbine-to-compressor coupling. The microstructure, hardness, and chemistry of the first and third-stage turbine wheels met engineering drawing requirements.
FADEC Data
Examination of maintenance data recorded by the FADEC revealed that at an undetermined time, the power turbine speed reached 104.56 percent. Additionally, the power turbine had been operated above 102 percent for a cumulative 138.43 seconds. Engine torque previously reached 108.4 percent and was above the torque limit for 0.1 seconds. It was not possible to determine the engine total time at each of the recorded exceedances.
Pilot and Weather Information
The pilot held a commercial pilot certificate with a rotorcraft-helicopter rating and a flight instructor certificate with a rotorcraft-helicopter rating. His most recent FAA first-class medical certificate was issued on February 27, 2007, on which date he reported 3,255 total hours of flight experience.
Weather conditions at Daytona Beach International Airport (DAB), about 17 nautical miles northeast, at 1853 included winds from 070 degrees at 4 knots, few clouds at 2,000 feet, broken clouds at 7,000 feet, and 10 statute miles visibility.