CEN13LA409

The airplane's unexpected encounter with a dust devil, which resulted in the loss of airplane control.

The pilot reported that, while in the airport traffic pattern, the airplane encountered very light turbulence. During short final approach and when the airplane was about 80 ft above ground level, the airplane suddenly encountered extreme turbulence, which the pilot described as far more violent than he had ever experienced. The airplane dropped vertically about 10 ft, suddenly entered a nose-up attitude, rolled right, and then struck the ground in a mostly nose-down attitude. Meteorological information indicated that, about the time of the accident, the atmosphere near the airport was unstable with variable light wind, warm dry air, and strong solar heating conditions, all of which are conducive to thermal activity and dust devil development. Further, several witnesses reported seeing dust devils and swirling wind in the area about the time of the accident. The pilot's report of extreme turbulence and his sudden loss of airplane control are consistent with the airplane's unexpected encounter with a dust devil.

The Airport/ Facility Directory, South Central U. S., indicated that SKX was a non-towered airport with a field elevation of 7,095 feet mean sea level (msl). Runway 04/22 was a 5,803 feet long by 75 feet wide asphalt runway. A Garmin GPSMAP 496 handheld GPS device was removed from the wreckage and examined at the NTSB Vehicle Recorder Laboratory, in Washington, D.C. On arrival, an exterior examination revealed the GPSMAP sustained negligible impact damage. The device was powered on normally and the memory was downloaded. The data extracted included 5 sessions from June 30, 20132 through July 10, 2013 and consisted of 1,379 total data points. The accident event was located from data recorded on July 10, 2013 and started from 10:30:03 to 11:07:35 MDT. The data points in the last few minutes showed a reduction in ground speed to about 75 to 65 knots ground speed. The last three data points showed the groundspeed decreased to 56, 52, and 56 knots A Rotax FLYdat engine data monitor removed from the wreckage was also examined at the NTSB Vehicle Recorder Laboratory. On arrival, an exterior examination revealed the FLYdat sustained negligible impact damage. The unit was powered on normally and connected to a PC via the serial port; however, the FLYdat software would not detect a connection between the FLYdat and the PC. The FLYdat was sent to the manufacturer, Rotax, located in Canada, for download with oversight by the Transportation Safety Board (TSB) of Canada. The data was obtained successfully. The data extracted included about 4 hours of data from its operating time of 559:59:40 to 563:56:20. The event flight was located as the last power cycle from an operating time of 563:18:00 to 563:56:20. No engine parameter exceedances were observed from the downloaded data. Data from the FLYdat was correlated with the Garmin GPSmap 496 data and converted from UTC operating time to MDT local time with an expected error of about plus or minus 15 seconds. At 10:35:16, the Garmin GPSmap 496's recorded groundspeed begins to increase with a corresponding increase in the FLYdat's recorded engine RPM and EGT at 563:23:40 FLYdat time. A Google Earth overlay was prepared which showed the airplane's flight path from GPS data during takeoff from SKX. At 10:35:16, the airplane is shown entering the runway and begins increasing its groundspeed. The data points shown lead up to the last recorded data point from 11:06:33 to 11:07:35. The data points in about the last minute and a half showed a reduction in engine RPM, constant with a power-off glide. According to the American Meteorological Society, a dust devil is defined as: "A well-developed dust whirl; a small but vigorous whirlwind, usually of short duration, rendered visible by dust, sand, and debris picked up from the ground ... Dust devils occasionally are strong enough to cause minor damage (up to F1 on the Fujita scale). Diameters range from about 3 meters to greater than 30 meters; their average height is about 200 meters, but a few have been observed as high as 1,000 meters or more … Although the vertical velocity is predominantly upward, the flow along the axis of large dust devils may be downward. Large dust devils may also contain secondary vortices. Dust devils are best developed on a hot, calm afternoon with clear skies, in a dry region when intense surface heating causes a very steep lapse rate of temperature in the lowest 100 meters of the atmosphere". An autopsy was performed on the instructor pilot by the Office of the Medical Investigator; Albuquerque, New Mexico. Forensic toxicology was performed on specimens from the instructor pilot by the FAA, Aeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma. The toxicology report stated that tests for Carbon Monoxide and for Cyanide were not performed and Ethanol was not detected in Urine. The report also stated Losartan was detected in Urine and Blood; Metoprolol was detected in Urine and Blood; and Salicylate was detected in Urine. The medications detected on toxicology are consistent with the flight instructor's known history of high blood pressure and would not degrade his ability to safely monitor the flying pilot. Forensic toxicology was performed on specimens from the pilot by the FAA, Aeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma. The toxicology report stated that tests for Carbon Monoxide and for Cyanide were not performed and Ethanol was not detected in Urine. The report also stated Bisoprol was detected in Blood. The medication detected on toxicology is consistent with a treatment for high blood pressure. At 1115 the Automated Surface Observation System at SKX reported calm wind, visibility 10 miles, clear of clouds, temperature 28 degrees Celsius (C), dew point 9 degrees C, and an altimeter setting of 30.39 inches of Mercury. The temperature and dew point relate to a resultant relative humidity of 30 percent. The high temperature of 31 degrees C occurred about an hour and a half after the accident. A local pilot, familiar with the area, reported there had been a lot of dust devils recently, and that was normal during mid to late summer. He described them as looking like a small tornado that can extend as high as about 500 feet. Most of the time they are visible from the air because of the dust and debris they carry. However, he reported that occasionally they can't be seen if they initiate on the runway or taxiway or some other place where they have no dust and debris. Another person who witnessed the accident and responded to the scene reported that as he later departed in his truck driving westbound on the main highway he saw "huge gusts of wind" and his truck was blown around by the wind. The Albuquerque (KABQ) soundings from 0600 and 2200 indicated a dry low-level environment with conditions favorable for strong thermals by 2200 to about 12,000 feet agl with a strong dry adiabatic lapse rate, and a Lifted Index of -3, or an unstable atmosphere. The Lifted Condensation Level (LCL) or the approximate base of the afternoon clouds was 9,394 feet agl (14,686 feet msl). The wind profile indicated wind speeds less than 15 knots through 40,000 feet, with variable wind direction. The 2200 sounding indicated strong heating, light surface wind, variable wind direction with height, unstable lapse rate, and showed strong support for thermal activity and dust devil development. The conditions required for Dust devils development include dry conditions, light wind, strong solar heating, and unstable atmosphere over the area resulted in favorable conditions for dust devil formation over the Taos region and could be expected near the time of maximum heating. While the AWOS did not detect any significant change in visibility during the period for any strong blowing dust over the area, isolated dust devils could be reasonably be expected. Primary motion in a dust devil is an upward movement of warm dry air, with wind speeds of 40 to 60 knots, depending on the diameter and strength of the vortices. Dust devil activity typically extends from 1000 until 1800 local time when winds are light and variable, with strong heating. Dust devils have contributed to many aircraft accidents and are more common at high elevation airports with fairly smooth terrain, with the majority of the accidents occurring in southern California, Arizona, Nevada, New Mexico, and western Texas. Most of the accidents also tend to occur during landing and takeoff, and have also been known to flip light aircraft while taxing or while unsecured on the ramp. In-flight, most accident cases indicate the aircraft pitched upwards and stalled, or rolled, leading to ground impact. The wreckage was about 300 feet northeast of the approach end of runway 22. About 50 feet from the main wreckage was an impact scar which corresponded to impact damage observed on the right wing tip, with another impact scar which corresponded to