Fawnskin, CA, USA
N91922
SONEX SONEX TRIGEAR
The sport pilot had purchased the airplane 2 days before the accident and was returning it to his home airport. Witnesses observed the airplane shortly after takeoff over a lake near the departure airport, and noted that the airplane was below the elevation of the surrounding terrain. As the airplane approached a cove, it banked left to almost 90 degrees. The nose dropped to a nearly-vertical attitude, and the airplane descended to ground contact. A postaccident examination of the airframe and flight controls revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. Examination of the engine determined that one of the four cylinders was carbon-fouled, which was likely the result of an overly rich fuel/air mixture due to the valve adjustment in that cylinder. Given the condition of the cylinder, the 80-horsepower (hp) engine was most likely producing only about 60 hp before the accident. The airplane was not equipped with wheel pants or fairings, which increased drag and further degraded the airplane's performance. Additionally, the density altitude at the time of the accident was over 8,200 ft. Although the pilot had a history of sleep apnea, he was using continuous positive airway pressure (CPAP) therapy, and it is unlikely that his sleep apnea contributed to the accident. Toxicological testing detected citalopram, a prescription medication used to treat depression and panic disorder. The investigation did not determine a definitive psychiatric diagnosis, but no operational evidence of pilot impairment was identified, and it is unlikely that the pilot's use of this medication contributed to the accident. The combination of high density altitude, airplane configuration, and cylinder fouling resulted in significantly decreased performance. It is likely that the airplane's margin above stall speed was minimal as the pilot attempted to climb the airplane after takeoff, and in his attempt to maneuver away from the rising, mountainous terrain, the pilot exceeded the airplane's critical angle of attack, which resulted in an aerodynamic stall/spin.
HISTORY OF FLIGHT On October 20, 2014, about 1045 Pacific daylight time, an experimental amateur-built Sonex Tri-gear, N91922, collided with terrain near Fawnskin, California. The pilot/owner was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The private pilot sustained fatal injuries. The airplane sustained substantial damage during the accident sequence. The cross-country personal flight departed Big Bear City Airport, Big Bear, California, about 1035 with a planned destination of Mesa, Arizona. Visual meteorological conditions (VMC) prevailed, and no flight plan had been filed. The pilot departed from runway 26; the airport was located about 1 mile east of Big Bear Lake. Witnesses observed the airplane about 200 feet above ground level over Big Bear Lake, but noted that this was below the level of surrounding terrain. As the airplane approached a cove, it banked left to almost 90 degrees. The nose dropped to a nearly vertical attitude until ground impact. PERSONNEL INFORMATION A review of Federal Aviation Administration (FAA) airman records revealed that the 60-year-old pilot held a private pilot certificate with a rating for airplane single-engine land. The pilot held a third-class medical certificate issued on March 8, 2005, with the limitation that he must have glasses available for near vision. The accident airplane was a light sport model, which does not require a medical certificate to operate. The pilot also held a light sport repairman certificate. No personal flight records were located for the pilot. The National Transportation Safety Board investigator-in-charge (IIC) obtained the aeronautical experience listed in this report from a review of the FAA airmen medical records on file in the Airman and Medical Records Center located in Oklahoma City, Oklahoma. The pilot reported on his most recent medical application that he had a total time of 500 hours with 6 hours logged in the previous 6 months. AIRCRAFT INFORMATION The pilot purchased the airplane 2 days prior to the accident. The airplane was a low wing, experimental amateur-built Sonex Tri-gear, serial number 811; the cowling was fiberglass; the remainder of the airplane was metal. A review of the airplane's logbooks revealed that it was manufactured in 2007. It had a total airframe time of 98.6 hours at the most recent conditional inspection on July 27, 2014. A logbook entry dated October 8, 2007, noted the following speeds during Phase 1 testing: Vso 40 mph, Vx 80 mph, and Vy 94 mph at a gross weight of 1,100 pounds and center-of-gravity location at 68 inches aft of datum. According to the engine logbook, the engine was a Volkswagon 2180 Aerovee, serial number 270, rated at 80 horsepower. The last maintenance recorded was an oil change on October 18, 2014, at a total time of 11.2 hours. Examination of the maintenance and flight department records revealed no unresolved maintenance discrepancies against the airplane prior to departure. Fueling records at Big Bear Airport established that the airplane was last fueled prior to the accident with the addition of 9.1 gallons of 100-octane low lead aviation fuel. METEOROLOGICAL INFORMATION An automated surface weather observation at Big Bear (KL35) (elevation 6,752 feet msl, 6 miles northeast of accident site) was issued 10 minutes prior to the accident. It indicated wind from 290 degrees at 4 knots, visibility 10 miles or greater, temperature at 16 degrees C, dew point 2 degrees C, and an altimeter setting at 30.18 inches of mercury. WRECKAGE AND IMPACT INFORMATION The IIC and inspectors from the FAA examined the wreckage on site the day of the accident. A complete report is part of the public docket for this accident. The airplane came to rest in a dry lakebed on a northeasterly heading. All components of the airplane remained with the main wreckage, and in position; a few pieces of plexiglass surrounded the main wreckage. There were no ground scars leading to the wreckage. The principle impact crater was under the propeller and fuselage. The nose of the airplane and the wing's leading edges exhibited up and aft crush damage. The engine partially separated, but maintained its position on the airframe. One of the wooden propeller's blades splintered near the hub, and the pieces were buried in the ground; the other blade splintered about half way to the tip. All flight controls remained in place and connected. The wreckage was recovered to a secure location for further examination. MEDICAL AND PATHOLOGICAL INFORMATION A postmortem examination was conducted by the San Bernardino County Medical Examiner. The cause of death was reported as the effect of blunt force injuries. The NTSB's medical officer reviewed the pilot's certified medical records on file with the FAA, the toxicology report, the autopsy report, the accident report, and interviewed the FAA medical case review physician. The medical officer prepared a factual report, which is part of the public docket for this accident. According to the FAA medical case review, the pilot reported on his 2005 airman medical application that he had sleep apnea that was treated with continuous positive airway pressure (CPAP) therapy, and he had carpal tunnel surgery the prior year. He reported no medication use, and the examining physician did not identify any abnormal findings. The sleep apnea was first diagnosed and treated with CPAP in February 2003, and the pilot provided the FAA medical certification division with diagnostic and treatment records that demonstrated successful treatment. The records did not identify any additional chronic medical issues, and the pilot was issued a third-class medical special issuance certificate that was not valid for operations requiring a medical certificate after March 31. 2007. The IIC interviewed a family member who stated that the pilot regularly used the CPAP machine, and said that it greatly enhanced his well-being. The autopsy did not identify any significant natural disease. The medical examiner's investigation identified a black bag containing a possible sleep apnea machine. The FAA Forensic Toxicology Research Team, Oklahoma City, Oklahoma, performed toxicological testing of specimens of the pilot. Analysis of the specimens contained no findings for carbon monoxide or volatiles. They did not perform tests for cyanide. The report contained the following findings for tested drugs: Citalopram detected in liver; Citalopram detected in blood (cavity), N-desmethylcitalopram detected in liver; N-desmethylcitalopram detected in blood (cavity). The San Diego County Forensic Toxicology Laboratory provided a toxicology report to San Bernardino County that identified 0.43 mg/l citalopram in cavity blood. Citalopram is a prescription medication used to treat a number of conditions including depression and panic disorder that is marketed as Celexa. The therapeutic level of citalopram in blood ranges from 0.030 to 0.400 mg/l. The FAA will consider a special issuance of a medical certificate for depression after 6 months of treatment if the applicant is clinically stable on one of four approved medications (citalopram, escitalopram, fluoxetine, and sertraline). TESTS AND RESEARCH The NTSB IIC examined the wreckage at Air Transport, Phoenix, Arizona, on October 26, 2014. A full report of the examination is contained within the public docket for this accident. Airframe The IIC established control continuity for all flight controls. The airframe was examined with no mechanical anomalies identified. Engine The engine had partially separated, but maintained its position on the airframe. There were no holes on the top of the crankcase or cylinders. No liquid streaks were observed on the airframe. The engine was left in place on the airframe. The crankshaft was manually rotated with the propeller. The crankshaft rotated freely, and the valves moved approximately the same amount of lift. The gears in the accessory case turned freely. Thumb compression was obtained on all cylinders. The spark plugs were removed; the gaps were similar, and the electrodes had no mechanical deformation. All electrodes were gray and clean except the top and bottom plugs for cylinder number two; both of those plugs contained heavy, black soot as did the inside of the combustion chamber. Gray color corresponded to normal operation according to the Champion Aviation Check-A-Plug AV-27 Chart; heavy, black soot was an indication of being carbon fouled. GPS A Garmin GPSMAP 296 was recovered at the accident site, and the NTSB Vehicle Recorder Division extracted data for 71 track logs including the accident flight. A detailed report is part of the public docket for this accident. The data indicated one aborted takeoff from runway 26 prior to the accident takeoff. During the aborted takeoff, the maximum derived groundspeed was 41 knots. The accident departure was about 3 minutes after the aborted takeoff. The data recorded about 4 minutes of flight; the last data point was at a GPS altitude of 7,011 feet (the highest recorded) and a ground speed of 59 knots (73 was the highest recorded). Due to buffering, the data recording may have ended before the accident event. ADDITIONAL INFORMATION Using the ambient weather conditions, the computed density altitude was 8,222 feet. Sonex provided owners with a flight manual that contained areas for recording items such as climb performance data, and indicated that this information should be recorded in Section 6 of the manual. No manual was recovered for this airplane, and the data was not available. The flight manual noted that slight engine roughness in flight could be caused by one or more spark plugs becoming fouled by carbon or lead deposits. A Sonex technical representative reported that the engine should have been developing about 60 horsepower under the conditions encountered. The representative opined that the heavy, black soot was an indication of a rich fuel mixture. Since it was confined to one cylinder, a reasonable cause would be valve adjustment/operation for that cylinder. The representative noted that the airplane should have been able to stay airborne if the airplane was properly built, tuned, faired and piloted; this airplane did not have wheel pants or fairings on any wheel. Sonex conducted flight testing on an airframe without wheel pants and fairings on just the main gear. With wheel pants and gear fairings installed; speed was 140 mph at 2,600 feet, and wide open throttle at 3,400 rpm; the speed was 127 mph at 2,600 feet at a cruise power of 3,100 rpm. Lack of wheel pants resulted in a 3 mph loss of cruise speed, and lack of wheel fairings resulted in a loss of an additional 10 mph. They indicated that no pant or fairing on the nose wheel could result in additional loss of performance.
The pilot's failure to maintain airspeed after takeoff, which resulted in an exceedance of the airplane's critical angle of attack and a subsequent aerodynamic stall/spin at low altitude. Contributing to the accident was the airplane's reduced climb performance due to a carbon-fouled engine cylinder, the airplane's lack of wheel pants and fairings, and the high density altitude conditions.
Source: NTSB Aviation Accident Database
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