NTSB Identification: DFW05FA086.
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Accident occurred Thursday, March 10, 2005 in Shelbyville, TX
Probable Cause Approval Date: 11/29/2006
Aircraft: Bell 206B-3, registration: N85BH
Injuries: 3 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

While in a slow flight out of ground effect the helicopter lost control and impacted heavily wooded (100-110 foot trees) terrain while on a United Stated Forest Service (USFS) prescribed fire mission. The prescribed fire was supported by the application of aerial ignition spheres utilizing a cabin mounted plastic sphere dispenser (PSD) machine. According to USFS operating procedures, PSD missions are typically flown at 50-300 feet above the top of the highest vegetation at airspeeds from 20-40 knots. While on the mission a radio distress call,"Mayday, Mayday, Mayday, we are going down," was heard on the mission operating frequency. According to USFS personnel, the voice making the distress call appeared to be that of the ignition specialist on board, not the pilot. No further communications were heard from the helicopter. Post accident examinations and testing of the engine, fuel control, and power turbine governor did not reveal conclusive evidence of mechanical failure. Examination of the airframe did not reveal evidence of a control system failure. Fuel calculations determined that the helicopter should have had about 36.9 gallons of usable fuel on board at the time of the accident. Evidence at the accident site showed some rotation signatures of dynamic drive components, although a power level could not be determined. The USFS inspection of the PSD machine did not reveal evidence of a malfunction that could have contributed to the accident. The helicopter was within weight and balance limits for the type of operation. The reason for the loss of control could not be determined.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The pilot's failure to maintain altitude and clearance for undetermined reasons.

Full narrative available

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