CircumFlightN900BM accident
NTSB ERA12CA352 · 2012-05-18 · Duncansville, PA
Docket — crew, injuries and powerplant
Summary
The pilot reported that the glider was towed to an altitude of 2,000 feet above ground level, released, and then flown for more than 2 hours without incident. He was subsequently looking for lift and performing "S" turns, while flying away from a ridgeline. During one of the "S" turns, he encountered a 200- to 300 foot-per-minute increase in lift and elected to continue the left turn. However, when the glider turned back toward the ridgeline, it encountered a large downdraft and loss of airspeed. The glider stalled, spun to the left, and struck trees. The glider's tail boom separated and both wings were substantially damaged. The pilot reported that there were no mechanical malfunctions or failures that would have precluded normal operation. He further stated that he should not have continued the left turn and that standard training techniques called for continuing to perform "S" turns when close to a ridge or mountain until the glider reaches an altitude of at least 200 to 300 feet above the highest point to provide adequate altitude to recover from possible stalls caused by downdrafts.
Full narrative
The pilot reported that the glider was towed to an altitude of 2,000 feet above ground level, released, and flown for more than 2 hours without incident. He subsequently was looking for lift and performing "S" turns, while flying away from a ridgeline. During one of the "S" turns, he encountered a 200 to 300 foot increase in lift and elected continue turning to the left. As the glider turned directly toward the ridgeline, it encountered a large downdraft and loss of airspeed. The glider stalled, spun to the left, and immediately struck trees. The glider's tail boom separated and both wings were substantially damaged. The pilot reported that he did not experience any mechanical malfunctions or failures during the flight. He further stated that he should not have continued the left turn and that standard training techniques called for continuing to do "S" turns when close to ridges or mountains until at least 200 to 300 feet above the highest point, which would provide for adequate altitude to recover from possible stalls caused by wind gusts.
Probable cause
The glider’s encounter with atmospheric lift conditions not sufficient to clear terrain, which resulted in an aerodynamic stall. Contributing to the accident was the pilot's decision to continue turning toward a ridgeline. The National Transportation Safety Board determined the probable cause of this accident.
Circumstances
- Event type
- Accident
- Highest injury
- Serious
- Weather conditions
- Visual Meteorological Cond
- Light condition
- Day
- Sky condition
- NONE
- Ceiling (ft)
- 0
- Visibility (sm)
- 10
- Wind direction
- 50
- Wind speed (kt)
- 5
- Distance from field
- 0.0
Aircraft
| Registration | Make | Model | Damage | FAR part |
|---|---|---|---|---|
| N900BM | — | — | SUBS | 091 |
Sequence of events
| # | Occurrence | Phase |
|---|---|---|
| 1 | Maneuvering-low-alt flying Windshear or thunderstorm | Climb |
| 2 | Maneuvering-low-alt flying Aerodynamic stall/spin defining | Climb |
| 3 | Uncontrolled descent Collision with terr/obj (non-CFIT) | Descent |