WPR12FA378

The pilot's inability to maintain airplane control due to an encounter with a microburst/downdraft that exceeded the climb performance capabilities of the airplane.

Witnesses observed the airplane operating in the airport traffic pattern. As the airplane turned from a crosswind to a downwind leg, witnesses estimated that the airplane was about 150 feet above ground level at a slow speed when it suddenly pitched downward and descended into the ground. Witnesses further stated that at the time of the accident, thunderstorms with strong wind, heavy rain, and lightning were arriving in the area. A regional radar mosaic for about the time of the accident depicted several scattered weather echoes with one defined cell of moderate-to-strong intensity just over the accident site. Archived lightning data for the time revealed seven in-cloud and cloud-to-ground lightning flashes within a 50-mile radius of the accident site; however, no cloud-to-ground lightning strikes were detected within 15 miles. The detection of lightning confirmed the presence of a cumulonimbus cloud in the area. Wreckage and impact signatures were consistent with a right-wing-low and nose-low impact. Postaccident examination of the airframe, flight control system, and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. Based on the witness observations and recorded weather data, it is likely that, as a result of the approaching thunderstorm, the airplane encountered a microburst or downdraft that exceeded the airplane's climb performance and resulted in a loss of airplane control.

HISTORY OF FLIGHT On August 30, 2012, about 1615 mountain daylight time, an Aircraft MFG & Development Company, CH 2000, N651AM, was substantially damaged when it impacted terrain while in the traffic pattern at the Nephi Municipal Airport (U14) near Nephi, Utah. The airplane was registered to private individuals and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. The certified flight instructor (CFI) and private pilot receiving instruction were fatally injured. Visual meteorological conditions prevailed, and no flight plan was filed for the instructional flight. The local flight originated from the Provo Municipal Airport near Provo, Utah, about 1500. According to witnesses located adjacent to the accident site, the airplane was observed on a southerly heading south of U14 before it turned left to a northerly heading at an altitude of about 150 feet above ground level (agl). Multiple witnesses reported that the airplane seemed to be traveling at a slow speed when it suddenly pitched downwards and descended into the ground. One witness stated that prior to the sound of impact the engine seemed to be at a high power setting. Witnesses further stated that at the time of the accident, a thunderstorm with strong wind, heavy rain, and lighting were present in the area. PERSONNEL INFORMATION The flight instructor, age 45, held a commercial pilot certificate with an airplane single-engine land and instrument airplane ratings. He also held a flight instructor certificate with airplane single-engine land and instrument ratings. A second-class airman medical certificate was issued on April 16, 2012, with no limitations stated. The pilot reported on his most recent medical certificate application that he had accumulated 950 total flight hours. The pilot receiving instruction, age 59, held a private pilot certificate with an airplane single-engine land rating, which was issued on August 29, 2012, based upon his Canadian private pilot certificate, which was issued on February 19, 2011. A third class airman medical certificate was issued to the pilot on March 23, 2010, with the limitation of "glasses must be worn." Review of the pilot's logbook revealed that as of the most recent logbook entry dated March 12, 2012, he had accumulated a total of 94.8 hours of flight time. AIRCRAFT INFORMATION The two-seat, low-wing, fixed-gear airplane, serial number (S/N) 20-1021, was manufactured in 2003. It was powered by a Lycoming O-235-N2C engine, serial number L-255755-15, rated at 116 horse power. The airplane was also equipped with a Sensenich fixed pitch propeller. The airplane was recently purchased by the pilot receiving instruction and another individual. Review of the airplane’s maintenance log books revealed an annual inspection was accomplished on August 17, 2012 with a tachometer time of 215.7 hours. The airplane underwent an export control examination by an FAA designated airworthiness representative on August 22, 2012 with a tachometer time of 216.0 hours and a hobbs/airplane total time of 242.5 hours. The tachometer indicated 217.6 hours at the accident site. METEOROLOGICAL INFORMATION A National Transportation Safety Board (NTSB) staff meteorologist prepared a factual report for the area and timeframe surrounding the accident. The National Weather Service Surface Analysis Chart for 1500 depicted the synoptic conditions over the region prior to the accident, which included a low pressure system over Wyoming with a cold front extending southwestward into northern Colorado and was a stationary front into Utah and Nevada. A high pressure system was located immediately west of the low and north of the front over western Wyoming. The station models surrounding the accident site depicted north-northwest wind at 10 to 15 knots, scattered clouds, with temperatures ranging from 88 degrees to 89 degrees Fahrenheit (F), with dew points between 45 degrees and 48 degrees F. The NWS Storm Prediction Center's Convective Outlook expected a general risk of thunderstorms over the region during the period. A review of the NWS regional radar mosaic for 1615 depicted several scattered weather echoes over the region southeast through south of Provo, Utah, with one area over the Nephi area with the maximum reflectivity’s near 45 dBZ. The accident site was located under the area of echoes. Nephi Municipal Airport (U14) is equipped with an Automated Weather Observation System (AWOS) for broadcasting local weather, however, it does not disseminate the observations to the FAA or NWS. The data obtained from MesoWest surrounding the period indicated that prior to the accident at 1559, Nephi reported a westerly wind from 260 degrees at 6 knots gusting to 19 knots, with scattered clouds at 11,000 feet, a temperature 88 degrees F, dew point 43 degrees F, relative humidity of 21 percent, altimeter 29.97 inches of mercury. The calculated density altitude was 8,029 feet. After the accident at 1659, the wind had shifted to the east and was reported from 080 degrees at 12 knots with gusts to 19 knots. There was also a 6 degree F decrease in temperature during the hour with rising dew point temperature, and falling pressure and subsequent rising pressure. The sounding parameters were for a warm dry low–level environment with a Lifted Index of -0.9, indicating a conditionally unstable environment favorable for scattered high based thunderstorm development. The Vertical Totals (VT) index of 37.1 indicated the potential for strong thunderstorms. The WINDEX or microburst potential measure of the downdraft instability estimated outflow winds near 37 knots, while the GOES Hybrid Microburst Index (HMI) algorithm of 29 indicated a strong potential for dry microbursts. Other indices such as the Microburst Day Potential Index (MDPI) of 0.3 indicated a low potential for microburst activity. The gust potentials ranged from 54 to 57 knots. The sounding wind profile indicated a surface wind from 345 degrees at 8 knots, with wind from the north through 4,000 feet agl, with winds backing to the southwest with height. Review of the observations and the satellite images from Provo at 1600 indicated that they were on the edge of the clouds with lightning being detected to the southeast. As the system moved northward with time, rain showers were reported from these cumulus congestus type clouds. Delta, Utah was also located under some high level cloud cover during the period, but not from the cloud mass that was identified over the accident site. Delta reported cumulonimbus type clouds in all quadrants during the period with blowing dust to the south and west, and rain showers after the accident. Price, Utah also on the eastern edge of the cloud area reported lightning activity to the west prior to the accident, and also indicated convective clouds WSR-88D base reflectivity images of the 0.5° elevation scan were completed at 1610:35, 1613:46, 1616:57, 1620:08, and 1623:20 respectively. The images depicted several scattered echoes develop across the region with one defined cell immediately south of the airport and over the accident site, that moved northeastward during the period around the time of the accident. The echoes observed were of moderate to strong intensity. Archived lightning data from 1600 through 1620 identified 7 in-cloud and cloud-to-ground lightning flashes within a 50 mile radius of the accident site. No cloud-to-ground lightning were detected within 15 miles of the accident site during the period. In-cloud lightning is typically observed during the towering cumulus or cumulus congestus stage of a developing thunderstorm, and continues into the dissipating stage. The detection of lightning confirms that the area of weather encountered by the accident airplane was associated with a cumulonimbus cloud, although a low topped one without the defined anvil outflow. For further