ASN Wikibase Occurrence # 170546
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| Date: | Monday 20 October 2014 |
| Time: | 10:45 |
| Type: |  Sonex Aircraft Sonex |
| Owner/operator: | Private |
| Registration: | N91922 |
| MSN: | 811 |
| Year of manufacture: | 2007 |
| Total airframe hrs: | 98 hours |
| Engine model: | Volkswagon Aerovee 2180 |
| Fatalities: | Fatalities: 1 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | West of Big Bear City Airport (L35), Big Bear City, CA -
 United States of America
|
| Phase: | Initial climb |
| Nature: | Private |
| Departure airport: | Big Bear, CA (L35) |
| Mesa, AZ (FFZ) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
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.
Probable Cause: 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.
Accident investigation:
 |
|
Sources:
NTSB
FAA register: http://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=91922
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 20-Oct-2014 19:02 | Geno | Added |
| 20-Oct-2014 19:08 | Geno | Updated [Location] |
| 20-Oct-2014 19:35 | harro | Updated [Embed code] |
| 21-Oct-2014 05:18 | Geno | Updated [Aircraft type, Registration, Cn, Operator, Phase, Departure airport, Source, Embed code, Narrative] |
| 21-Oct-2014 06:33 | Anon. | Updated [Aircraft type, Registration, Cn, Embed code] |
| 21-Oct-2014 16:17 | Geno | Updated [Operator, Phase, Departure airport, Source] |
| 23-Oct-2014 17:49 | Geno | Updated [Nature, Destination airport, Source] |
| 28-Oct-2014 08:52 | ABG | Updated [Phase] |
| 21-Dec-2016 19:28 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 13-Mar-2017 18:08 | PiperOnslaught | Updated [Departure airport, Destination airport, Source, Narrative] |
| 13-Mar-2017 18:08 | harro | Updated [Aircraft type] |
| 19-Aug-2017 13:53 | ASN Update Bot | Updated [Other fatalities, Destination airport, Source, Embed code, Narrative] |
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