Mackay, ID, USA
N35MP
Stemme GMBH & CO S10-VT
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.
**This report was modified on 5/3/2010** HISTORY OF FLIGHT On August 19, 2009, at 1702 mountain daylight time, a Stemme GMBH & CO S10-VT, N35MP, collided with mountainous terrain near Mackay, Idaho. The pilot was operating the glider under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The certificated commercial pilot, who held private pilot privileges in gliders, was killed, and the motor glider was substantially damaged by impact forces. The local personal flight departed Arco-Butte County Airport, Arco, Idaho, about 1525. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot departed Arco with two other gliders, with the intention of soaring in the area. The group planned to return to Arco by 1800. The two other pilots in the group reported that they were in radio contact with the accident pilot until about 1630, at which time he reported that he was close to the Mackay Reservoir, and was having difficulty gaining sufficient lift to climb out of the area. The pilots attempted to establish radio communications about 45 minutes later, but were unable to contact him. They stated that this was not unusual, and they were not concerned due to the limited range of their radio transceivers. The remaining members of the group decided to return to Arco about 1715 due to a lack of sufficient lift in the area. One pilot reported that soaring conditions were, "mediocre," the weather was "docile." He additionally stated that they had been warned by other pilots of the possibility of turbulence in the area. The accident pilot did not return by the planned regroup time; by 1915 the group became concerned, and contacted the Arco airport manager to report the pilot's late arrival. Local law enforcement and the Civil Air Patrol initiated a search, and the glider was located the following afternoon on the face of White Knob Summit, 6 miles southwest of the Mackay Reservoir. An impact damaged Garmin Rino 120 handheld radio transceiver/global positioning systems receiver (GPS) was recovered from the glider. The unit was sent to the National Transportation Safety Board Office of Research and Engineering for data extraction. The data revealed the entire flight sequence beginning at Arco, and continuing on an arching northwesterly track towards the accident location. The data showed that the glider departed Arco and began a series of 10 left climbing turns over Butte City to a GPS altitude of 9,888 feet. Over the course of the next 3 1/2 minutes, the glider maintained a course of about 20 degrees magnetic for 4 miles towards the southern peaks of the Lost River Range. By the time it had reached the peaks, the glider's altitude had dropped to 9,203 feet. Over the next 8 1/2 minutes it began a series of 12 climbing left turns until it reached an altitude of 13,242 feet. For about the next hour the glider tracked northwest, following the peaks of the range, and continuing a cycle of five groups of climbing turns, followed by meandering descents. Throughout the cycles the maximum altitude attained was 14,951 feet. During this portion of the flight the glider maintained clearance from the ground of between 1,600 and 5,000 feet. At an altitude of 14,182 feet the glider changed heading towards the southwest, descending and flying over Mackay Airport (U62). Ten minutes later, at an altitude of 11,539 feet, the glider cleared the peak of a ridge line adjacent to White Knob Summit by about 600 feet, and changed heading to the northwest. For the remaining 6 minutes the glider continued to track a descending northern path on the west side of the peaks of the mountain ridges. During this portion of the flight the glider maintained a terrain clearance of between 250 and 1,400 feet agl. The glider then turned to the east and entered a valley area, clearing the terrain by about 270 feet (10,501 GPS). The glider then began a left turn; about 270 degrees into the turn the glider had descended about 70 feet and changed course beginning a descending turn to the right. The glider continued the turn with the last recorded altitude at 10,326 feet on a heading of 101 degrees true. The wreckage was located in line with the final course, about 400 feet east of the last recorded track point, at an elevation of 9,730 feet msl. The ground speeds throughout the majority of the flight varied between 158 and 46 mph. The last 8 ground speeds, recorded over a period of about 25 seconds, varied between 59 and 62 mph, with the two final speeds indicating 56 and 44 mph consecutively. PERSONNEL INFORMATION The 78 year-old-pilot held a commercial pilot certificate with ratings for rotorcraft-helicopter, and instrument helicopter. He additionally held private privileges for airplane single-engine land, airplane single-engine sea, airplane multiengine land, instrument airplane, and glider. The pilot held a second-class medical certificate issued on July 1, 2009. It had limitations that the pilot must wear corrective lenses and possess glasses for near/intermediate vision. Recent pilot flight records were not available. The pilot reported on his most recent medical certificate application in March 20, 2009, that he had amassed a total of 20 flight hours during the 6 months prior to the application. The pilot was involved in an airplane accident on January 3, 2009 (NTSB accident number WPR09LA071), for which he submitted an NTSB Pilot/Operator Aircraft Accident Report. In the report he stated a total flight time for all aircraft of 11,000+ hours, 1,200 of which were in gliders. The NTSB determined the probable cause of this accident to be, ‘A loss of engine power due to fuel exhaustion as a result of the pilot’s 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 1/2 inches, and its maximum takeoff and landing weight was 1,874 pounds. A turbocharged, four-stroke, four cylinder Rotax 914 engine was mounted within the airframe aft of the main cabin, and powered a retractable, nose mounted composite propeller. The pilot purchased the glider in November 2001. The engine and airframe logbooks indicated that at the time of the last annual inspection, dated March 10, 2009, the glider had accumulated a total flight time of 428.2 hours. The March 2008 annual inspection entry reported a total glider time of 412 hours. A friend of the pilot stated that 2 days prior to the accident, the pilot reported that the airspeed indicator had failed. The pilot brought this to the attention of an A&P mechanic, but before the mechanic began troubleshooting, the airspeed indicator began to work again. The friend was not aware of the pilot making any further attempts to resolve the anomaly prior to the flight. Published documentation from the glider's manufacturer stated that the propeller blades extend into the airstream automatically by centrifugal force only when the engine is started. Additionally, the documentation details a 10-step checklist of items that need to be configured prior to changing from glider to powered flight. According to the flight manual applicable to the accident glider, the stalling speed with the flaps in the retracted position is 56 mph. The stalling speed in the flaps extended landing configuration is 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 units were sent to the National Transportation Safety Board Office of Research and Engineering for data extraction; however, examination of the unit revealed that impact damage had destroyed all recorded flight information. WRECKAGE AND IMPACT INFORMATION The glider came to rest within a valley on a steep southwestern facing slope of White Knob Summit. The crest of the slope was about 900 feet above the main wreckage. The valley to the west descended into the Copper Basin area, located at an elevation of about 7,600 feet. The first identified point of impact was characterized by a flat, 15-foot-wide, near vertical swath cut through the tree branches of a 20-foot-tall tree. The immediate area was surrounded by similar trees and brush, none of which displayed damage. The left wing came to rest about 10 feet to the north of the damaged tree, and was partially attached to the main cabin and right wing, which continued on a heading of about 030 degrees magnetic. The tail section was largely undamaged, separated from the main cabin at the forward bulkhead, and located about 10 feet uphill. The entire cabin area was fragmented around the engine cage. A crater containing clear plastic fragments similar in appearance to windshield material was located about 15 feet downhill from the cabin. The left wing spar had become fractured about midspan, and its entire leading edge surfaces were fragmented. About 80 percent of the right wing skins had become separated from, and lay adjacent to, the wing spar. A TruTrak Systems ADI Flight Instrument was located within the main cabin and indicated a 45 degrees left bank, and 500-foot-per-minute (fpm) descent. All major sections of the glider were accounted for at the accident site. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was conducted by Western Pathology Associates. The cause of death was reported as blunt force trauma Toxicological tests on specimens from the pilot were performed by the FAA Civil Aeromedical Institute. The results were negative for all screened drug substances and ingested alcohol. Refer to the toxicology report included in the public docket for specific test parameters and results. METEOROLOGICAL INFORMATION The closest weather reporting facility to the accident site was Friedman Memorial Airport, Hailey, Idaho, located approximately 42 miles west of the accident site, at an elevation of 5,318 feet. The airport was equipped with an Automated weather Observation System (AWOS-3) and reported the following weather conditions at 1645: Winds from 200 degrees at 4 knots; visibility 30 miles; sky clear below 12,000 feet; temperature 27 degrees Celsius (C); dew point 5 degrees C; and altimeter 30.07 inches of Mercury (Hg). The infrared band 4 image taken at 1732 from the National Climatic Data Center Geostationary Operations Environmental Satellite 12 (GOES-12) depicted clear skies over the accident site. The GOES-12 water vapor image depicted high level moisture extending over northern Idaho, with several moisture channel darkening areas associated with subsidence over southern Idaho, central Montana, Wyoming, and Utah. One area of moisture channel darkening was located oriented in an east-to-west direction in the immediate vicinity of the accident site. The closest upper air sounding or rawinsonde observation (RAOB) was from the National Weather Service, Boise, Idaho, site, number 72681, located approximately 109 miles west of the accident site at an elevation of 2,867 feet. The 1800 sounding wind profile on August 19, 2009, indicated surface wind from 330 degrees at 7 knots, with wind direction slowly veering to the north-northwest with height. Wind speeds were less than 20 knots from the surface through 18,000 feet. The mean 0 to 6 kilometer (km) winds were from 330 degrees at 12 knots. For further weather information, see the Meteorological Factual Report in the public docket for this accident. TESTS AND RESEARCH Airframe The wreckage was extensively damaged by impact forces. The nose cone and entire cabin, including all instruments and cockpit controls, were fragmented. The wing spars remained attached at the center spar box, although the fuselage structure had broken away. The air brakes, flaps, and their associated mechanisms were damaged, and as such, their deployment status could not be determined. The rudder cables were continuous from the rudder horns through to the aft cabin where they had separated in a broomstraw pattern. Three canopy latch pins were still affixed within their respective locking holes. The remaining canopy hinges and pins were located, and exhibited witness marks consistent with a closed canopy position at the time of impact. The push-pull control tubes within both wings and the fuselage were fragmented. All associated bell cranks were firmly affixed to their attach points. The elevator push-pull tube and associated bellcrank was attached within the tail section, and continuous through to the area where the tail had separated from the fuselage. Two oxygen cylinders were located within the wreckage. One cylinder appeared intact, was capped, and according to its pressure gauge, contained a residual amount of oxygen. The second cylinder sustained impact damage in the area of the valve head. Rotation of the valve revealed that it was in the open position, and its gauge indicated that it was empty. Fragmented sections of oxygen line were observed distributed within the cockpit area. Engine The engine remained attached within its mounting cage. The retractable propeller and its associated gearbox had separated from the fuselage. The propeller was observed in the retracted position; the leading edge surfaces were free of gouges and abrasions. The trailing edges of one blade exhibited scratches and nicks that corresponded to the position of the propeller mounting bracket, with the blade in the retracted position. Removal of the engines top spark plugs revealed dark colored electrodes with light yellow and green deposits. The plug electrodes were intact, and did not exhibit signs of mechanical damage. The engine was rotated by hand via the crankshaft, and thumb compression was noted in firing order on all cylinders. Removal of the oil filter revealed a flow of clear oil, free of obvious contaminants. Rotation of the turbocharger induction impeller by hand revealed that it rotated freely and smoothly. No rotational scoring of the impeller shroud was observed. The exhaust pipe outlet exhibited dark brown deposits and was free of oily residue. The magneto switch was observed in the off position. The fuel shutoff valve had sustained impact damage and its position could not be verified. No pre-impact mechanical anomalies were identified during the examination.
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.
Source: NTSB Aviation Accident Database
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