Accident Overview
On July 10, 2013, at 1107 mountain daylight time, a Flight Design GmbH CTSW special light sport airplane, registration N424CT, was substantially damaged after impacting terrain during landing at Taos Regional Airport (SKX) in Taos, New Mexico. The flight instructor was killed, and the pilot sustained serious injuries. The airplane was registered to and operated by a private individual. Day visual meteorological conditions prevailed at the time of the accident, and no flight plan had been filed for the instructional flight conducted under 14 Code of Federal Regulations Part 91. The airplane had departed SKX at 1035 for a local flight.
While in the traffic pattern, the airplane was in continuous very light turbulence and was on a stabilized power-off approach with the engine at idle power. The flaps were set to 30 degrees, and the airspeed was 12 to 15 knots above stalling speed. The pilot reported that he and the flight instructor expected to touch down about 1,000 feet past the runway approach threshold, and neither had noted the presence of dust devils. On short final approach, the airplane suddenly encountered extreme turbulence, which the pilot described as far more violent than any he had ever experienced.
A witness saw the airplane on final approach when it was "bouncing around" and seemed to be having trouble. It dropped vertically about 10 feet, then suddenly went into a nose-up attitude, rolled to the right, and struck the ground mostly nose down. After impact, the airplane came to rest inverted about 300 feet short of the runway. Several people immediately rendered aid to both occupants. There was a significant fuel spill, but no postimpact fire.
Flight and Weather Conditions
At 1115, the Automated Surface Observation System at SKX reported calm wind, visibility 10 miles, clear of clouds, temperature 28 degrees Celsius, dew point 9 degrees Celsius, and an altimeter setting of 30.39 inches of Mercury. The temperature and dew point indicated a relative humidity of 30 percent. The high temperature of 31 degrees Celsius occurred about an hour and a half after the accident.
A local pilot familiar with the area reported that there had been many dust devils recently, which is normal during mid to late summer. He described them as looking like small tornadoes 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, but occasionally they cannot be seen if they initiate on surfaces without 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. Soundings from Albuquerque indicated a dry low-level environment with conditions favorable for strong thermals, a strong dry adiabatic lapse rate, and a Lifted Index of -3 (unstable atmosphere). The wind profile indicated wind speeds less than 15 knots through 40,000 feet with variable wind direction. The 2200 sounding showed strong heating, light surface wind, variable wind direction with height, unstable lapse rate, and strong support for thermal activity and dust devil development. Wind speeds in a dust devil can reach 40 to 60 knots. Dust devil activity typically extends from 1000 until 1800 local time when winds are light and variable with strong heating.
Aircraft and Personnel Information
The accident aircraft was a high-wing, fixed landing gear, single-engine light sport airplane manufactured in 2005 (serial number 05-06-02). It was powered by a 100-horsepower Rotax 912 ULS engine (serial number 5645006) driving a Neuform CR3-65-47-101.6 three-blade wood composite ground adjustable propeller. The airplane was equipped with a Garmin GPSmap 496 handheld GPS and a Rotax FLYdat engine data monitor.
A postaccident review of maintenance documents showed that a condition inspection was completed on October 2, 2012, at a total time of 534.0 hours. At the time of the accident, the airplane had accumulated 563.5 hours. The pilot reported an operating weight of 1,200 pounds; the maximum operating weight was 1,320 pounds. The recommended speed for a normal landing with 40 degrees of flap was about 62 knots, and the stalling speed in the landing configuration with 40 degrees of flap was about 39 knots.
The flight instructor, age 71, held an FAA airline transport pilot certificate with ratings for airplane single engine and multiengine land, and type ratings in B-737, B-747, and DC-10. He also held a current flight instructor certificate and a third-class medical certificate issued on August 15, 2012, with a restriction "must wear corrective lenses." His total pilot experience was 33,785 hours. The pilot, age 72, held an FAA private pilot certificate with ratings for airplane single engine and instrument airplane. He held an expired third-class medical certificate issued on August 15, 2012, with a restriction "must have available glasses for near vision." However, he was flying a light sport aircraft, which requires only a valid driver's license. The pilot reported 3,365 total hours, with 564 hours in the accident airplane and about 12 hours in the previous three months.
Wreckage and Investigation
The wreckage was located about 300 feet northeast of the approach end of runway 22. An impact scar about 50 feet from the main wreckage corresponded to damage on the right wing tip, with another scar corresponding to damage on the nose gear, propeller, and forward fuselage. The airplane came to rest inverted with the nose oriented to about 020 degrees. The left wing, left flap, and left aileron remained attached; the right wing was partially separated at the wing root, but the right flap and right aileron remained attached. The leading edge of the outboard two feet of the right wing tip showed evidence of terrain impact on the lower side, consistent with a right-wing-low and nose-low attitude at impact.
The nose gear, engine, engine mount, and firewall remained attached with significant impact crushing. The propeller hub remained attached to the engine flange, but all three blades were impact-separated at the blade grips; only fragments were found. The lower forward fuselage was fragmented and separated. Both pilot seats were partially detached, but the attach points and latches for the four-point restraint systems remained intact and operable; some webbing had been cut for victim removal. The instrument panel was impact-damaged and separated, but individual instruments mostly remained intact. The mounting structure for the activation handle of the ballistic recovery parachute system was twisted; emergency responders reinstalled the safety pin. The rocket motor had not been activated and was undamaged.
The main landing gear was impact-damaged and partially separated. The fuselage from the center of the cockpit aft remained mostly intact with no direct impact evidence. The tail skid showed no impact. The stabilator and trim tab had no obvious damage; the vertical fin was impact-damaged at the top, and the rudder was damaged and partially separated. All flight control surfaces remained attached or partially attached, and control continuity was examined where possible. No evidence of preimpact mechanical malfunctions or failures was found.
A Garmin GPSMAP 496 handheld GPS was removed from the wreckage and downloaded. Data showed the accident event from 10:30:03 to 11:07:35 MDT. In the last few minutes, ground speed reduced to about 75 to 65 knots, with the last three data points at 56, 52, and 56 knots. A Rotax FLYdat engine data monitor was also downloaded; no engine parameter exceedances were observed. Correlation with GPS data indicated the airplane entered the runway at 10:35:16 and began increasing groundspeed. The last approximately 1.5 minutes showed a reduction in engine RPM, consistent with a power-off glide.
The on-scene examination revealed no evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation. An autopsy was performed on the instructor pilot; forensic toxicology detected Losartan, Metoprolol, and Salicylate in urine and blood, consistent with treatment for high blood pressure and not degrading his ability to safely monitor the flying pilot. Toxicology on the pilot detected Bisoprol in blood, consistent with treatment for high blood pressure.