Pilot Debrief

Stemme GMBH & CO S10-VT near Mackay, ID — 2009-08-19

Final reportWPR09FA409
Sign in to save
Date
2009-08-19
Location
Mackay, ID, USA
Airport
AOC
Aircraft
Stemme GMBH & CO S10-VT
Registration
N35MP
Category
Glider
Highest injury
Fatal
Fatalities
1
Phase of flight
Descent

Probable cause

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.

NTSB narrative

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.

Analysis

Primary failure mode
Controlled flight into terrain
First missed decision gate
Pilot could have chosen to return to Arco earlier due to lack of lift.

NTSB coding

Evidence available

  • Photos
  • 14 docket documents
View NTSB final reportView NTSB docket

Docket documents14

Related mishaps