Individually Owned: 150,657
Corporate Owned: 137,281
Arco-Butte Airport
Aircraft Accident/Incident Report
Mackay, Idaho 83251
Wednesday, August 19, 2009 17:02 MDT
NTSB Narrative Summary Released at Completion of Accident
The pilot departed in his glider, as a group of three, with the intention of soaring in the area. During the flight the pilot reported via radio that he was unable to find favorable soaring conditions. He did not return to the airport at the predetermined time, and the wreckage was located on the steep slope of a summit the following day. Flight data recovered from the pilot's handheld GPS unit revealed a track that was consistent with ridge and thermal soaring. For about the first hour of flight the glider maintained ground clearances of between 1,600 and 5,000 feet. For the last 16 minutes of flight the glider continued ridge soaring with reduced ground clearances of between 250 and 1,400 feet. The glider then crested a peak and returned to a valley area performing a figure eight turn. During the last turn the recorded ground speed fell below the stall speed of the glider. Analysis of the weather at the accident site indicated the presence of turbulence and downdrafts, in addition to wind directions that would have indicated an airspeed that was even lower than the ground speed recorded by the GPS. Glider instrumentation, wreckage, and ground scars were consistent with a stall/spin event. The engine did not appear to be operating at the time of the accident and the damage to the propeller was consistent with it being stowed. The glider was having intermittent problems with its airspeed indicator a few days prior to the flight; however, impact damage prevented an assessment of the system's status. Such a failure in flight could have hindered the pilot’s ability judge stall speed. All major sections of the glider were accounted for at the accident site, and post accident examination of the engine and airframe revealed no anomalies that would have prevented normal operation.
NTSB Probable Cause Narrative
The pilot's failure to maintain adequate airspeed while maneuvering in terrain-induced turbulent wind conditions, resulting in an inadvertent entry into a stall/spin.
Event Information
| Type of Event | Accident |
| Event Date | 8/19/2009 |
| Event Day of the Week | Wednesday |
| Time of Event | 1702 |
| Event Time Zone | Mountain Daylight Time |
| Event City | Mackay |
| Event State | IDAHO |
| Event Country | -- |
| Zipcode of the event site | 83251 |
| Event Date Year | 2009 |
| Event Date Month | 8 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | 435226N |
| Event Location Longitude | 1134517W |
| Event Location Airport | Arco-Butte |
| Event Location Nearest Airport ID | AOC |
| Indicates whether the acc/inc occurred off or on an airport | Off Airport/Airstrip |
| Distance from airport in statute miles | 28 |
| Degrees magnetic from airport | -- |
| Airport Elevation | 5332 |
| Weather Briefing Completeness | -- |
| Investigator's weather source | Weather Observation Facility |
| Time of the weather observation | 1645 Mountain Daylight Time |
| Direction of event from weather observation facility (degrees) | 210 |
| Weather Observation Facility ID | SUN |
| Elevation of weather observation facility | 5318 |
| Distance of event from weather observation facility (units?) | 42 |
| Time Zone of the weather observation | MDT |
| 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) | 30 |
| Air Temperature at event time (in degrees celsius) | 27 |
| Dew Point at event time (in degress fahrenheit) | 5 |
| Wind Direction (degrees magnetic) | 200 |
| Variable Wind Indicator | Wind direction could be determined |
| Wind Speed (knots) | 4 |
| Wind Velocity Indicator | -- |
| Wind Gust Indicator | Not Gusting |
| Wind Gust (knots) | -- |
| Altimeter Setting at event time (in. Hg) | 30.07 |
| Density Altitude (feet) | -- |
| Intensity of Precipitation | -- |
| METAR weather report | -- |
| Event Highest Injury | Fatal |
| On Ground, Fatal Injuries | -- |
| On Ground, Minor Injuries | -- |
| On Ground, Serious Injuries | -- |
| Injury Total Fatal | 1 |
| Injury Total Minor | -- |
| Injury Total None | -- |
| Injury Total Serious | -- |
| Injury Total All | 1 |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 26861 |
| NTSB Notification Source | FAA NW Region Operations Cente |
| NTSB Notification Date | -- |
| NTSB Notification Time | -- |
| Fiche Number and/or location -used to find docket information | -- |
| Date of most recent change to record | May 3 2010 1:07PM |
| User who most recently changed record | broda |
| Basic weather conditions | Visual Meteorological Cond |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N35MP |
| NTSB Number | WPR09FA409 |
| Missing Aircraft Indicator | -- |
| Federal Aviation Reg. Part | Part 91: General Aviation |
| Type of Flight Plan filed | None |
| Flight plan Was Activated? | -- |
| Damage | Substantial |
| Aircraft Fire | None |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | Stemme GMBH & CO |
| Aircraft Model | S10-VT |
| Aircraft Series Identifier | -- |
| Aircraft Serial Number | 11011 |
| Certified Max Gross Weight | 1874 |
| Aircraft Category | Glider |
| Aircraft Registration Class | -- |
| Aircraft is a homebuilt? | No |
| Flight Crew Seats | -- |
| Cabin Crew Seats | -- |
| Passenger Seats | -- |
| Total number of seats on the aircraft | 2 |
| Number of Engines | 1 |
| Fixed gear or retractable gear | Retractable |
| Aircraft, Type of Last Inspection | Annual |
| Date of Last Inspection | Mar 10 2009 12:00AM |
| Airframe hours since last inspection | -- |
| Airframe Hours | 428 |
| ELT Installed | Yes |
| ELT Activated | Yes |
| ELT Aided Location of Event Site | Yes |
| ELT Type | C91-A |
| Aircraft Owner Name | Thierry N Thys |
| Aircraft Owner Street Address | -- |
| Aircraft Owner City | Oakland |
| Aircraft Owner State | CA |
| Aircraft Owner Country | USA |
| Aircraft Owner Zipcode | 94605 |
| Operator is an individual? | Yes |
| Operator Name | Thierry N Thys |
| Operator Same as Owner? | Yes |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | Yes |
| Operator Street Address | -- |
| Operator City | Oakland |
| Operator State | CA |
| Operator Country | USA |
| Operator Zip code | 94605 |
| Operator Code | -- |
| Owner has at least one certificate | None |
| Other Operator of large aircraft? | No |
| 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) | Personal |
| Second Pilot on Board | No |
| Departure Point Same as Event | No |
| Departure Airport Code | AOC |
| Departure City | Arco |
| Departure State | ID |
| Departure Country | USA |
| Departure Time | 1525 |
| Departure Time Zone | MDT |
| Destination Same as Local Flt | dest & departure same, accident can occur anywhere |
| Destination Airport Code | AOC |
| Destination City | Arco |
| Destination State | ID |
| Destination Country | USA |
| Specific Phase of Flight | -- |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | May 3 2010 1:08PM |
| User who most recently changed record | broda |
| 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 | -- |