Individually Owned: 150,657
Corporate Owned: 137,281
N/A Airport
Aircraft Accident/Incident Report
Sunburst, Montana 59482
Saturday, August 18, 2012 12:15 MDT
NTSB Narrative Summary Released at Completion of Accident
The pilot was maneuvering the helicopter in a 3-foot in-ground-effect hover in preparation for departure on a border patrol flight when he heard a loud “bang,” which was immediately followed by a decay in the main rotor rpm and a right yaw. The pilot performed an autorotation, and, after touchdown, he conducted the emergency shutdown procedures.
The postaccident airframe examination revealed that the tail rotor moved independently of the main rotor. Further examination revealed that the aft flange of the main gearbox transmission drive shaft was liberated from its flex coupling at the engine output. The castellated nuts that secured the flex coupling to the aft flange of the shaft were found loose, and the bolts were sheared. An examination of the bolts and flex coupling determined that the nuts were most likely hand-tightened and that cotter pins were not installed on three attachment bolts between the flex coupling and flange portion of the drive shaft.
A review of the maintenance records revealed that, about 75 flight hours before the accident, the engine had been removed so that maintenance personnel could perform a modification. Maintenance personnel removed the bolts to the engine-to-main gearbox flex coupling and then partially reassembled the flex coupling bolts, which was not in accordance with the helicopter’s maintenance manual engine removal procedure. Although no comments were found in the engine maintenance logbooks indicating that the flex coupling was disassembled from the tail portion of the helicopter, the maintenance performed involved disassembly of the drive shaft. The cotter pins likely were not installed on the attachment bolts during the most recent maintenance, which allowed the nuts to start to back out of the three attachment bolts.
NTSB Probable Cause Narrative
The improper installation of the engine-to-main gearbox flex coupling, which resulted in the failure of the flex coupling and a loss of power to the rotor system during takeoff.
Event Information
| Type of Event | Accident |
| Event Date | 8/18/2012 |
| Event Day of the Week | Saturday |
| Time of Event | 1215 |
| Event Time Zone | Mountain Daylight Time |
| Event City | Sunburst |
| Event State | MONTANA |
| Event Country | -- |
| Zipcode of the event site | 59482 |
| Event Date Year | 2012 |
| Event Date Month | 8 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | 485309N |
| Event Location Longitude | 1115346W |
| Event Location Airport | N/A |
| 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 | Pilot |
| Time of the weather observation | |
| Direction of event from weather observation facility (degrees) | -- |
| Weather Observation Facility ID | -- |
| Elevation of weather observation facility | -- |
| Distance of event from weather observation facility (units?) | -- |
| Time Zone of the weather observation | -- |
| Lighting Conditions | Day |
| Lowest Ceiling Height | -- |
| Lowest Non-Ceiling Height | -- |
| Sky/Lowest/Cloud Conditions | Clear |
| Sky Condition for Lowest Ceiling | None |
| Visibility Runway Visual Range (Feet) | -- |
| Visibility Runway Visual Value (Statute Miles) | -- |
| Visibility (Statute Miles) | 10 |
| Air Temperature at event time (in degrees celsius) | 27 |
| Dew Point at event time (in degress fahrenheit) | -4 |
| Wind Direction (degrees magnetic) | -- |
| Variable Wind Indicator | Variable |
| Wind Speed (knots) | -- |
| Wind Velocity Indicator | Light and Variable |
| Wind Gust Indicator | Not Gusting |
| Wind Gust (knots) | -- |
| Altimeter Setting at event time (in. Hg) | 30.15 |
| 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 | 2 |
| Injury Total Serious | -- |
| Injury Total All | -- |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 32720 |
| NTSB Notification Source | DHS |
| NTSB Notification Date | -- |
| NTSB Notification Time | -- |
| Fiche Number and/or location -used to find docket information | -- |
| Date of most recent change to record | May 20 2014 7:49PM |
| User who most recently changed record | kelz |
| Basic weather conditions | Visual Meteorological Cond |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N3939A |
| NTSB Number | WPR12TA364 |
| Missing Aircraft Indicator | -- |
| Federal Aviation Reg. Part | Public Use |
| Type of Flight Plan filed | None |
| Flight plan Was Activated? | No |
| Damage | Substantial |
| Aircraft Fire | None |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | AMERICAN EUROCOPTER LLC |
| Aircraft Model | AS350B3 |
| Aircraft Series Identifier | -- |
| Aircraft Serial Number | 4806 |
| Certified Max Gross Weight | 5225 |
| 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 | 6 |
| Number of Engines | 1 |
| Fixed gear or retractable gear | Fixed |
| Aircraft, Type of Last Inspection | Annual |
| Date of Last Inspection | Mar 30 2012 12:00AM |
| Airframe hours since last inspection | 75 |
| Airframe Hours | 889 |
| ELT Installed | Yes |
| ELT Activated | No |
| ELT Aided Location of Event Site | Unknown |
| ELT Type | -- |
| Aircraft Owner Name | DEPT OF HOMELAND SECURITY CUSTOMS & BORDER |
| Aircraft Owner Street Address | -- |
| Aircraft Owner City | WASHINGTON |
| Aircraft Owner State | DC |
| Aircraft Owner Country | USA |
| Aircraft Owner Zipcode | 20229-0001 |
| Operator is an individual? | No |
| Operator Name | DEPT OF HOMELAND SECURITY CUSTOMS & BORDER |
| Operator Same as Owner? | Yes |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | No |
| Operator Street Address | -- |
| Operator City | Great Falls |
| Operator State | MT |
| Operator Country | USA |
| Operator Zip code | -- |
| Operator Code | -- |
| 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) | -- |
| Second Pilot on Board | No |
| Departure Point Same as Event | Yes |
| Departure Airport Code | -- |
| Departure City | Sunburst |
| Departure State | MT |
| Departure Country | USA |
| Departure Time | 1215 |
| Departure Time Zone | MDT |
| Destination Same as Local Flt | crash at destination city |
| Destination Airport Code | -- |
| Destination City | Sunburst |
| Destination State | MT |
| Destination Country | USA |
| Specific Phase of Flight | -- |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | May 21 2014 6:05PM |
| User who most recently changed record | stam |
| Since inspection or accident | Last Inspection |
| Event Location Runway Number and Location | N/A |
| Runway Length | -- |
| Runway Width | -- |
| Sight Seeing flight | No |
| Air Medical Flight | No |
| Medical Flight | -- |