Stonewall, CO, USA
C-GGBT
Hawker Beechcraft 58P
The pilot maneuvered the twin-engine pressurized airplane to a level attitude about 18,000 feet mean sea level (msl). Approximately 30 minutes later, while approaching the downwind side of a ridge of mountains, the airplane entered an uncontrolled descent and impacted mountainous terrain. During the last radio transmissions from the pilot, he reported having serious difficulties; however, he was unsure of the exact nature of the problem. Following the loss of radar contact, a pilot from a passing airplane approached the accident area and located the wreckage. As the pilot circled the wreckage, he encountered a mountain wave event and elected to depart the area. A meteorological study of weather conditions in the accident area indicated the potential for severe mountain wave activity at the time of the accident. There were also numerous pilot reports specifically identifying encounters with mountain waves and/or severe or extreme turbulence at flight levels close to the accident area. A postaccident examination of the airplane revealed no anomalies that would have precluded normal operation.
HISTORY OF FLIGHT On December 20, 2008, at 1951 mountain standard time, a twin-engine Hawker Beechcraft 58P airplane, C-GGBT, was destroyed when it impacted terrain following a loss of control near Stonewall, Colorado. The private pilot and the sole passenger sustained fatal injuries. The airplane was registered to and operated by Mauroil International Inc., of Calgary, Alberta, Canada. Night visual meteorological conditions prevailed and an instrument flight rules (IFR) flight plan was filed for the 14 Code of Federal Regulations Part 91 personal flight. The first leg of the two part cross-country flight had originated earlier that day from the Great Falls International Airport (GTF), Great Falls, Montana, and had concluded at the Pueblo Memorial Airport (PUB), Pueblo, Colorado, for a planned fuel stop. The second leg of the flight originated from PUB at 1915 with the Santa Fe Municipal Airport (SAF), Santa Fe, New Mexico, as the intended destination. A review of radar information revealed that following departure the airplane climbed to and leveled off at 18,000 feet mean sea level (MSL). (All altitudes listed in this report are MSL unless otherwise noted) Approximately 32 minutes later the airplane was flying on a heading of 207 degrees and was approaching a ridge of mountains that ran in a north south direction. When the airplane was about four and a half miles east of the ridgeline, it began an uncontrolled descent toward an area of rising mountainous terrain. During the last radio transmissions from the pilot, he reported having serious difficulties; however, he was unsure what the problem was. The last known radar position placed the airplane at 12,800 feet and one mile east of Vermejo Peak with a summit of 13,367 feet. A short time later a ground fire was reported by a passing airplane in the vicinity of the accident airplane’s last known coordinates. The pilot from the passing airplane submitted a written statement about what he observed while circling over the accident airplane. The pilot was flying a pressurized Cessna 210, equipped with an Allison 250 turbo-propeller engine that was capable of producing 450 horse power (HP). While approaching the accident area at 19,000 feet the Cessna pilot spotted a ground fire that he believed was the accident airplane. While circling the wreckage, he realized that his airplane was descending and added engine power thinking it was poor piloting technique. After reporting the fire to air traffic control (ATC), he noticed that his airplane’s attitude was now down to 18,500 feet and the engine was already at full power. The Cessna pilot informed ATC that he was in an area of downdraft and they cleared him for a block altitude of 17,000 to 19,000 feet. During this time his airplane continued an uncontrolled descent at 500 feet per minute (fpm), and the Cessna pilot estimated that the airplane should have been climbing at 1,000 fpm. The Cessna pilot elected to leave the area to the south and the rate of descent began to slow until he was able to maintain altitude. The Cessna pilot characterized the downdraft as an area of “mountain wave.” The wreckage was located on December 21, 2008, at an elevation of approximately 12,077 feet. A helicopter crew was able to approach the accident site and confirm that the occupants had been fatally injured before operations were suspended due to deteriorating weather conditions. Because of snow, search and rescue personnel were unable to recover the bodies of the pilot and passenger until May 8, 2009. PERSONNEL INFORMATION The pilot, age 67, held a Canadian issued private pilot certificate with ratings for airplane single-engine land, multi-engine land, and instrument airplane. His last Transport Canada third-class medical was issued on November 26, 2007, with the limitation of “Glasses Must Be Worn.” The pilot’s logbook was not recovered during the course of the investigation. An insurance application submitted on February 4, 2008, listed the pilot’s total flight time as 1,634 hours, with 84 flight hours in the previous 12 months, and 21 flight hours in the preceding 90 days. The pilot’s flight hours in this make and model of airplane are unknown; however, the insurance application listed a total of 400 hours in a Beech 95-A55. The date of his last flight review is unknown. AIRCRAFT INFORMATION The 1981-model Hawker Beechcraft 58P, serial number TJ-373, was a pressurized, low wing, twin engine airplane, equipped with a retractable landing gear, and was configured for six occupants. The airplane was powered by two, Teledyne Continental Motors (TCM), direct drive, horizontally opposed, fuel injected, air-cooled, turbo-charged, six-cylinder engines. The engines were TSIO-520s, serial numbers 237278-R and 518129, rated at 325 horsepower at 2,700 rpm, and were driving three-bladed constant speed McCauley propellers. The airplane’s airframe and engine logbooks were not recovered during the course of the investigation; however, partial copies of records were received. According to these records the airplane's most recent annual inspection was completed on June 27, 2008, with an airframe total time of 3,571 hours. At the time of annual inspection the left engine had accumulated an estimated 98 hours since a major overhaul on September 5, 2006, and the right engine had accumulated approximately 473 hours since a major overhaul on July 5, 2007. The McCauley propellers had been installed new on July 5, 2007. Fuel receipts revealed that the airplane was last fueled on December 20, 2008, at PUB with 109.30 gallons of 100LL aviation fuel. METEOROLOGICAL INFORMATION A review of meteorological conditions for Colorado revealed that at 2100 a stationary front stretched from Wyoming to northeastern New Mexico near, but to the east of the Continental Divide. Most stations in the eastern-half of Colorado reported clear skies with light and variable winds at the surface. At 1952, the automated weather observing system at the San Luis Valley Regional Airport/Bergman Field (ALS), Alamosa, Colorado, located 45 nautical miles northwest from the site of the accident, reported wind from 80 degrees at 6 knots, 10 statute miles visibility, clear of clouds, temperature 16 degrees Fahrenheit, dew point 7 degrees Fahrenheit, and a barometric pressure setting of 30.04 inches of Mercury. To assess the potential for mountain wave activity and retrieve quantitative data concerning the severity of any mountain waves present, the RAwinsonde OBservation Program (RAOB) was utilized. Three separate vertical profiles of wind and temperature were acquired: 1) a RAwinsonde weather balloon launch at 1700, from the Albuquerque International Sunport Airport (ABQ), Albuquerque, New Mexico, located 141 nautical miles south-southwest of the accident site, 2) a North American Mesoscale (NAM) model atmosphere for the accident location initialized at 2000, and 3) an atmosphere measured by an aircraft departing the Denver International Airport (DEN), Denver, Colorado, in a southward direction about 2019. With the ABQ RAwinsonde launch, severe wave activity was found to occur about 16,200 feet, with theoretical downdrafts estimated to be in excess of 4,500 fpm. Additionally, moderate/severe wave activity was found to exist at altitudes greater than 40,000 feet. When considering the NAM model atmosphere, light wave activity was found to occur about 16,600 feet, with theoretical downdrafts estimated to be approximately 550 fpm. Severe wave activity was found to be centered about 23,000 feet. The aircraft-measure atmosphere from the DEN departing aircraft revealed light wave activity at altitudes of 16,000 feet and 18,000 feet, with theoretical downdrafts of approximately 300 fpm each. Severe wave activity was found to occur at 22,000 feet, with moderate/severe wave activity at 36,000 feet. There were numerous pilot reports (PIREPs) of turbulence over the state of Colorado on December 20, 2008. Many of these reports specifically identified encounters with mountain waves and/or severe or extreme turbulence at flight levels close to the upset location for the accident airplane. COMMUNICATIONS According to a transcript of air traffic control communications, the accident flight was cleared for takeoff from PUB at 1915. At 1931:05, the accident pilot contacted the Denver air route traffic control center sector 27 radar controller (referred to as “Denver Center”) and reported that the flight was level at its assigned altitude of flight level 180 (18,000 feet pressure altitude), and the controller acknowledged. At 1947:37, the Denver Center controller asked the pilot to verify the flight’s altitude, and the pilot replied, “uh … we’ve having some problems here sir we’re just trying to rectify it we’re going back up from seventeen to eighteen.” At 1947:48, the controller acknowledged and stated “…when you’re able maintain flight level one eight zero just be advised where you’re at minimum IFR altitude [is] one six thousand if you think you need something different uh let me know.” At 1948:08, the pilot requested an altitude of 16,000 feet, stated to the controller that he “[didn’t] know what the problem is,” and asked the controller, “what kind of a ground speed readout do you have on us?” The controller then cleared the flight to maintain 16,000 feet, provided the local altimeter information, and advised the pilot that his display showed the airplane with a ground speed of 135 knots. The pilot asked the controller to repeat the ground speed information and then replied to the controller, “one three five knots thank you.” At 1949:26, the pilot stated, “uh golf bravo tango sir we’re having some serious difficulties here.” The controller responded, “… roger maintain your highest possible altitude a vector away from terrain would be to the right but that would be into the wind what would you like to do sir?” At 1949:43, the pilot replied, “uh.” No further radio communications were received from the pilot. WRECKAGE AND IMPACT INFORMATION Because of snow, investigators were unable to reach the accident site until June 16, 2009. The wreckage was located on the north side of Vermejo Peak in a steep area of granite scree, at an elevation of 12,077 feet, and approximately 1,290 feet below the summit. Based on the projection of debris the estimated impact heading was approximately 130 degrees; however, the airplane’s attitude at impact could not be determined. During the spring as the snow melted the wreckage had moved around and several pieces had slid downhill. Once all major components of the airplane were accounted for, the wreckage was recovered and examined at Beegles Aircraft Service Inc., in Greely, Colorado. The fuselage was nearly consumed by the post crash fire. A vacuum driven artificial horizon instrument was located and disassembled for inspection. Rotational scoring signatures were found inside the gyroscope housing; suggesting it was operational during impact. Both wings were found separated from the fuselage and exhibited thermal damage. Parts of the right wing were also consumed in the post crash fire. Both ailerons remained attached in their respective positions. The left flap was found separated and portions of the right flap remained attached to the wing. The flap actuator measurements corresponded to the retracted flap position. Both fuel selectors were determined to be selected to their “ON” positions by applying air pressure through the fuel supply lines. The left main landing gear up-lock roller was engaged in the up-lock mechanism suggesting the landing gear was in the retracted position at impact. The thermally damaged empennage section, consisting of the horizontal stabilizer, left and right elevators, the vertical stabilizer and the rudder, remained attached to each other and was located downhill from the main wreckage. Control cables stretched from the fuselage wreckage to the empennage section. The left and right elevator trim tab actuator measurements corresponded to an approximate 5 to 10 degree tab up position. The rudder trim tab actuator measurement corresponded to a 0 to 5 degree tab right position. Due to thermal damage and the condition of the wreckage, only partial control continuity could be established for each aileron and the elevator. Rudder control continuity was established from the rudder pedals aft to the rudder. Both engines had been exposed to the elements for six months before they could be recovered and examined. Both were found attached to the airframe via control cables and hoses and exhibited rust and corrosion. Neither engine crankshaft could be rotated due to accident damage. Three holes were drilled in each crankcase above cylinders 1, 3, and 6 to facilitate an examination using a lighted borescope. All cylinders remained attached in their respective positions. Various spark plugs were removed and each cylinder examined via a lighted borescope. The internal combustion chambers exhibited a material consistent with that of combustion deposits. The cylinder bores were free of scoring within the visible cylinder bore ring travel area. All examined spark plugs exhibited a material consistent with that of corrosion in the electrode area. All visible spark plug electrodes exhibited normal operating signatures when compared to the Champion Check-A-Plug comparison card. All four engine magnetos exhibited impact and or thermal damage and could not be tested. The left and right engine fuel pumps were removed and examined. Neither fuel pump drive shaft could be rotated by hand. Each fuel pump was disassembled and the fuel pump vanes along with each fuel pump drive coupling were found intact. No indication of hard particle passage was observed in the fuel pump housings. The relief valve seats exhibited no debris or obstructions, no damage was observed in the diaphragms, and no indication of fuel leakage was observed in the chamber side of the relief valves. Both engine oil filters were opened and visually examined. The oil filter elements exhibited no abnormal particles or debris and displayed a residue of oil. The left vacuum pump drive shaft was found intact and the right vacuum pump drive shaft exhibited thermal damage. Neither shaft could be turned by hand. Disassembly of each unit revealed that the left rotor was fractured in a manner consistent with impact damage and the right rotor and vanes appeared unremarkable. Both turbochargers remained attached to their respective engines and exhibited impact damage. Neither turbocharger shaft could be rotated by hand. No indications of cracks or exhaust leaks were observed on the turbine, compressor, or center housings. All turbine and compressor blades were intact. Both propellers had separated from the engine crankshaft flanges and were found a distance from the main wreckage. All 6 blades were accounted for and each exhibited leading and trailing edge gouging, “S” bending, cordwise scratches, and polishing. Most propeller blade tips had been separated during impact. The damage to each propeller was consistent with the engines producing power at the time of impact. No anomalies were found with either the engines or airframe that would have contributed to the loss of control. MEDICAL AND PATHOLOGICAL INFORMATION The El Paso County Corner, located in Colorado Springs, Colorado, performed an autopsy on the pilot on May 11, 2009. The manner of death was listed as, “Accident.” The FAA, Toxicology Accident Research Laboratory, located in Oklahoma City, Oklahoma, reported that they did not receive specimens for toxicological testing. ADDITIONAL INFORMATION A search of the Canadian Civil Aviation Daily Occurrence Reporting System (CADORS) revealed a report filed December 18, 2008. The report stated that the accident airplane had departed Springbank Airport (YBW), Calgary, Alberta, Canada, on an instrument flight rules (IFR) flight to Casper, Wyoming. When the airplane was about 40 miles southeast of YBW, the pilot indicated that he was experiencing incorrect airspeed measurements and was also having altimeter issues. The pilot subseq
The pilot's inadvertent flight into mountain wave activity resulting in a loss of control and subsequent impact with mountainous terrain.
Source: NTSB Aviation Accident Database
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