History of Flight
On August 19, 2009, at 1702 mountain daylight time, a Stemme GMBH & CO S10-VT motor glider, registration N35MP, collided with mountainous terrain near Mackay, Idaho. The pilot was operating under 14 CFR Part 91 as a certified commercial pilot with private glider privileges. The local personal flight departed Arco-Butte County Airport, Arco, Idaho, at about 1525. Visual meteorological conditions prevailed, and no flight plan was filed.
The pilot departed with two other gliders intending to soar in the area, planning to return by 1800. The other pilots reported radio contact until about 1630, when the accident pilot stated he was near the Mackay Reservoir and struggling to gain sufficient lift. Attempts to re-establish contact about 45 minutes later were unsuccessful. The group decided to return to Arco around 1715 due to poor lift conditions. One pilot described soaring conditions as "mediocre" and the weather "docile," and noted warnings of possible turbulence.
When the accident pilot did not return, the group contacted the Arco airport manager at 1915. Local law enforcement and the Civil Air Patrol initiated a search, locating the glider the following afternoon on the face of White Knob Summit, 6 miles southwest of the Mackay Reservoir.
An impact-damaged Garmin Rino 120 handheld GPS/radio was recovered and sent to the NTSB for data extraction. The data showed the flight sequence from Arco: the glider climbed in left turns over Butte City to 9,888 feet GPS altitude, then tracked northwest, alternating between climbing turns and descents, with maximum altitude 14,951 feet. Terrain clearance varied from 1,600 to 5,000 feet. At 14,182 feet, the glider turned southwest toward Mackay Airport, then northwest, descending with terrain clearance of 250 to 1,400 feet AGL. It then turned east into a valley, clearing terrain by about 270 feet. A left turn of about 270 degrees was followed by a descending right turn; the last recorded altitude was 10,326 feet on a heading of 101 degrees true. Wreckage was found about 400 feet east of the last track point at an elevation of 9,730 feet.
Ground speeds during the flight ranged from 158 to 46 mph. The final eight ground speeds over about 25 seconds varied between 59 and 62 mph, with the last two at 56 and 44 mph.
Personnel Information
The 78-year-old pilot held a commercial certificate with rotorcraft-helicopter and instrument helicopter ratings, plus private privileges for airplane single-engine land/sea, multiengine land, instrument airplane, and glider. He held a second-class medical certificate issued July 1, 2009, with limitations for corrective lenses and glasses for near/intermediate vision. Recent flight records were unavailable; on his March 20, 2009 medical application, he reported 20 flight hours in the preceding 6 months.
The pilot was involved in a prior airplane accident on January 3, 2009 (NTSB WPR09LA071), for which he submitted a report stating total flight time of 11,000+ hours, with 1,200 in gliders. The NTSB probable cause for that accident was fuel exhaustion due to inadequate preflight planning. In 2002/2003, the pilot flew the accident glider on a long-distance expedition from Point Barrow, Alaska, to Cape Horn, Chile.
Glider Information
The dual-seat, retractable-gear motor glider was manufactured by Stemme AG (Germany) in 1998. Its wingspan was 75 feet 5.5 inches, maximum takeoff and landing weight 1,874 pounds. It was powered by a turbocharged Rotax 914 engine mounted aft of the cabin, driving a retractable nose-mounted composite propeller. The pilot purchased the glider in November 2001.
Logbooks indicated total flight time at the last annual inspection (March 10, 2009) as 428.2 hours; the March 2008 inspection showed 412 hours. A friend stated that two days before the accident, the pilot reported an airspeed indicator failure that briefly self-resolved; no further action was taken.
Manufacturer documentation stated propeller blades extend automatically by centrifugal force when the engine starts, and a 10-step checklist is required for transition from glider to powered flight. The flight manual listed stalling speed with flaps retracted at 56 mph, and flaps extended at 53 mph.
Flight Recorders
The glider was equipped with a Cambridge Aero Instruments GPS-NAV 25 Secure Flight Data Recorder and a Magellan Blazer 12 handheld GPS. Both were sent to the NTSB for data extraction, but impact damage destroyed all recorded flight information.
Wreckage and Impact Information
The glider came to rest in a valley on a steep southwest-facing slope of White Knob Summit, about 900 feet below the crest. The first impact point was a 15-foot-wide, near-vertical swath through tree branches. The left wing was about 10 feet north of the damaged tree, partially attached to the main cabin and right wing, which continued on a heading of about 030 degrees magnetic. The tail section, largely undamaged, separated at the forward bulkhead and was found about 10 feet uphill. The cabin area was fragmented around the engine cage. A crater with clear plastic fragments (likely windshield) was about 15 feet downhill.
The left wing spar fractured at midspan, with fragmented leading edges. About 80% of right wing skins separated from the spar. A TruTrak Systems ADI Flight Instrument indicated a 45-degree left bank and 500-foot-per-minute descent. All major sections were accounted for.
Medical and Pathological Information
An autopsy conducted by Western Pathology Associates reported cause of death as blunt force trauma. Toxicological tests by the FAA Civil Aeromedical Institute were negative for all screened drugs and alcohol.
Meteorological Information
The closest weather reporting facility was Friedman Memorial Airport, Hailey, Idaho, about 42 miles west, elevation 5,318 feet. At 1645, AWOS-3 reported winds from 200 degrees at 4 knots, visibility 30 miles, sky clear below 12,000 feet, temperature 27°C, dew point 5°C, altimeter 30.07 inches Hg.
GOES-12 satellite imagery at 1732 showed clear skies over the accident site, with high-level moisture over northern Idaho and subsidence over southern Idaho. The closest upper air sounding (Boise, ID) at 1800 indicated surface wind from 330 degrees at 7 knots, veering north-northwest with height, winds less than 20 knots through 18,000 feet, mean 0-6 km winds from 330 degrees at 12 knots.
Tests and Research
Airframe examination revealed extensive impact damage. The nose cone and cabin were fragmented; wing spars remained attached at the center spar box. Control systems were damaged; deployment status of air brakes, flaps, and associated mechanisms could not be determined. Rudder cables separated in a broomstraw pattern. Three canopy latch pins were in place; canopy witness marks indicated a closed position at impact. Push-pull tubes were fragmented; bell cranks were affixed. The elevator push-pull tube was continuous through the tail separation point.
Two oxygen cylinders were found: one intact with residual oxygen, the other with impact damage to the valve head, valve open, and empty. Fragmented oxygen lines were in the cockpit.
Engine examination: The engine remained in its mounting cage; the retractable propeller and gearbox separated. The propeller was in the retracted position with leading edges free of gouges. One blade trailing edges had scratches matching the mounting bracket. Spark plugs had dark electrodes with light yellow/green deposits, intact. Hand rotation produced thumb compression in firing order. Oil filter showed clear, contaminant-free oil. The turbocharger impeller rotated freely. Exhaust pipe had dark brown deposits, no oil. The magneto switch was off; the fuel shutoff valve position could not be verified due to impact damage. No pre-impact mechanical anomalies were identified.