Individually Owned: 150,657
Corporate Owned: 137,281
None Airport
Aircraft Accident/Incident Report
Brownwood, Texas 76802
Sunday, November 26, 2006 17:30 CST
NTSB Narrative Summary Released at Completion of Accident
The helicopter pilot experienced a sudden "explosion" followed by an uncommanded left yaw while initiating an approach. During the autorotation the pilot was forced to increase collective pitch in order to clear a berm resulting in a loss of main rotor RPM. The helicopter landed hard and remained in the upright position. A review of the turbine engine's maintenance records and work orders revealed the engine had been repaired and inspected in December 2005 for "a sudden stoppage." At that time, the compressor, gearbox, and turbine were replaced. A teardown examination of the engine revealed that the aft end of the turbine-to-compressor coupling had fractured in the region where it mated with the turbine splined adapter. The coupling fracture resulted in a loss of continuity in the N1 drive train and an overspeed failure of the first stage turbine wheel. Metallurgical examination of the fracture surfaces of the remnants of the first stage turbine wheel revealed there was no fatigue fractures. Examination of the splines in the aft end of the coupling and on the pieces from the fractured section revealed fretting and a fractured spline tip in the area of contact with the turbine spline adapter. There was non-uniform wear on 16 consecutive external splines on the turbine splined adapter and there was also non-uniform wear of the splines in the area where the adapter mated with the aft end of the turbine-to-compressor coupling. When the engine was disassembled, there was a discrepancy noted between the thickness of the shims (used for alignment of the gas producer and power turbine drive trains) on the mounting pad between the exhaust collector support and the accessory gearbox than what had been entered in the engine logbook or what was etched on the exhaust collector support. In addition, the balance marks on the spur adapter gear shaft and the turbine-to-compressor coupling were not aligned. According to the Rolls Royce 250-C30 series Overhaul Manual, the balance marks were required to be aligned during re-assembly of the engine. The Overhaul Manual also stated that the cracks found on the vertical fire shield could have been as a result of "abnormally high engine vibration."
NTSB Probable Cause Narrative
The fracture of the turbine-to-compressor coupling and subsequent overspeed failure of the first stage turbine wheel as result of the improper re-assembly of the engine by maintenance personnel. A contributing factor was the lack of suitable terrain for the forced landing.
Event Information
| Type of Event | Accident |
| Event Date | 11/26/2006 |
| Event Day of the Week | Sunday |
| Time of Event | 1730 |
| Event Time Zone | Central Standard Time |
| Event City | Brownwood |
| Event State | TEXAS |
| Event Country | -- |
| Zipcode of the event site | 76802 |
| Event Date Year | 2006 |
| Event Date Month | 11 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | 314722N |
| Event Location Longitude | 0985714W |
| Event Location Airport | None |
| Event Location Nearest Airport ID | -- |
| Indicates whether the acc/inc occurred off or on an airport | Off Airport/Airstrip |
| Distance from airport in statute miles | -- |
| Degrees magnetic from airport | -- |
| Airport Elevation | -- |
| Weather Briefing Completeness | -- |
| Investigator's weather source | Weather Observation Facility |
| Time of the weather observation | 1725 Central Standard Time |
| Direction of event from weather observation facility (degrees) | -- |
| Weather Observation Facility ID | BWD |
| Elevation of weather observation facility | 1300 |
| Distance of event from weather observation facility (units?) | 3 |
| Time Zone of the weather observation | CST |
| Lighting Conditions | Day |
| Lowest Ceiling Height | 6000 |
| Lowest Non-Ceiling Height | 4300 |
| Sky/Lowest/Cloud Conditions | Few |
| Sky Condition for Lowest Ceiling | Broken |
| Visibility Runway Visual Range (Feet) | -- |
| Visibility Runway Visual Value (Statute Miles) | -- |
| Visibility (Statute Miles) | 10 |
| Air Temperature at event time (in degrees celsius) | 21 |
| Dew Point at event time (in degress fahrenheit) | 13 |
| Wind Direction (degrees magnetic) | 160 |
| Variable Wind Indicator | Wind direction could be determined |
| Wind Speed (knots) | 8 |
| Wind Velocity Indicator | -- |
| Wind Gust Indicator | Not Gusting |
| Wind Gust (knots) | -- |
| Altimeter Setting at event time (in. Hg) | 30.02 |
| Density Altitude (feet) | -- |
| Intensity of Precipitation | -- |
| METAR weather report | -- |
| Event Highest Injury | None |
| On Ground, Fatal Injuries | -- |
| On Ground, Minor Injuries | -- |
| On Ground, Serious Injuries | -- |
| Injury Total Fatal | -- |
| Injury Total Minor | -- |
| Injury Total None | 3 |
| Injury Total Serious | -- |
| Injury Total All | -- |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 22141 |
| NTSB Notification Source | FTW FSDO |
| NTSB Notification Date | Nov 26 2006 12:00AM |
| NTSB Notification Time | -- |
| Fiche Number and/or location -used to find docket information | DMS |
| Date of most recent change to record | Aug 30 2007 12:18PM |
| User who most recently changed record | NTSB\lema |
| Basic weather conditions | Visual Meteorological Cond |
| FAA District Office | Fort Worth FAA/FSDO |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N805SB |
| NTSB Number | DFW07LA027 |
| Missing Aircraft Indicator | -- |
| Federal Aviation Reg. Part | Part 91: General Aviation |
| Type of Flight Plan filed | Company VFR |
| Flight plan Was Activated? | Yes |
| Damage | Substantial |
| Aircraft Fire | Ground |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | Bell |
| Aircraft Model | BH 206L-3 |
| Aircraft Series Identifier | -- |
| Aircraft Serial Number | 51192 |
| Certified Max Gross Weight | 4150 |
| Aircraft Category | Helicopter |
| Aircraft Registration Class | -- |
| Aircraft is a homebuilt? | No |
| Flight Crew Seats | -- |
| Cabin Crew Seats | -- |
| Passenger Seats | -- |
| Total number of seats on the aircraft | 4 |
| Number of Engines | 1 |
| Fixed gear or retractable gear | Fixed |
| Aircraft, Type of Last Inspection | AAIP |
| Date of Last Inspection | Oct 1 2006 12:00AM |
| Airframe hours since last inspection | -- |
| Airframe Hours | 10604.8 |
| ELT Installed | No |
| ELT Activated | No |
| ELT Aided Location of Event Site | No |
| ELT Type | -- |
| Aircraft Owner Name | Air Evac EMS, Inc. |
| Aircraft Owner Street Address | -- |
| Aircraft Owner City | West Plains |
| Aircraft Owner State | MO |
| Aircraft Owner Country | USA |
| Aircraft Owner Zipcode | 65775 |
| Operator is an individual? | No |
| Operator Name | -- |
| Operator Same as Owner? | Yes |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | Yes |
| Operator Street Address | -- |
| Operator City | -- |
| Operator State | -- |
| Operator Country | -- |
| Operator Zip code | -- |
| Operator Code | EVCA |
| Owner has at least one certificate | None |
| Other Operator of large aircraft? | -- |
| Certified for Part 133 or 137 Operation | -- |
| Operator Certificate Number | -- |
| Indicates whether an air carrier operation was scheduled or not | -- |
| Indicates Domestic or International Flight | -- |
| Operator carrying Pax/Cargo/Mail | -- |
| Type of Flying (Per_Bus / Primary) | Positioning |
| Second Pilot on Board | No |
| Departure Point Same as Event | No |
| Departure Airport Code | ABI |
| Departure City | Abilene |
| Departure State | TX |
| Departure Country | USA |
| Departure Time | 1650 |
| Departure Time Zone | CST |
| Destination Same as Local Flt | -- |
| Destination Airport Code | -- |
| Destination City | Brownwood |
| Destination State | TX |
| Destination Country | USA |
| Specific Phase of Flight | Descent |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | Aug 16 2007 10:55AM |
| User who most recently changed record | CASH |
| Since inspection or accident | Last Inspection |
| Event Location Runway Number and Location | NA |
| Runway Length | -- |
| Runway Width | -- |
| Sight Seeing flight | No |
| Air Medical Flight | Yes |
| Medical Flight | -- |