WPR11FA450

The pilot’s execution of an abrupt maneuver, likely to avoid birds, which resulted in a stall and spin.

While approaching the airport at the conclusion of a 4-hour flight, the pilot announced his intention over the common traffic frequency to join the traffic pattern. A short time later, an undiscernible distress transmission was made over the frequency. A few seconds later, the airplane was observed spiraling to the ground. Global positioning system data recovered from the airplane revealed that it was traveling at an appropriate airspeed for entry into the downwind leg of the traffic pattern with a sufficient margin above the stall speed to maintain flight. It then made an abrupt left turn, resulting in a spiral dive, which progressed into a spin. A postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. No evidence of a bird-strike was found, and review of radar data did not reveal the presence of other aircraft in the vicinity just prior to the accident. However, radar data did reveal that the airplane passed through a cluster of primary targets (with no altitude information) at the time of the accident. Such primary targets could potentially be radar system anomalies, thermal air currents, or bird reflections. According to a bird mitigation specialist, large birds, or flocks of smaller birds, are often present at that time of year, and such birds typically fly circling patterns in thermal air currents at traffic pattern altitudes. The pilot’s abrupt maneuver during the approach was consistent with an avoidance maneuver. The maneuver, which was calculated to be a 65-degree angle of bank to the left, most likely placed the airplane into an accelerated stall condition, which developed into a spin. The airplane was loaded toward its aft center of gravity limit, which could have increased its pitch sensitivity, thereby exacerbating the turn. A successful recovery from an unintentional stall-spin at pattern altitude is extremely unlikely.

HISTORY OF FLIGHT On September 15, 2011, at 1223 mountain daylight time, an experimental amateur-built Cone (Vans Aircraft) RV-6A, N641JC, collided with terrain on the property of an elementary school in West Jordan, Utah. The pilot was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. The private pilot sustained fatal injuries. The airplane sustained substantial damage during the accident sequence. The cross-country personal flight departed Sierra Vista Municipal Airport-Libby Army Airfield, Fort Huachuca/Sierra Vista, Arizona, at 0822 mountain standard time, with a planned destination of South Valley Regional Airport, Salt Lake City, Utah. Visual instrument meteorological conditions prevailed, and no flight plan had been filed. The airplane was equipped with a Garmin GPSMap 496 global positioning system (GPS) receiver. The unit sustained impact damage, and was sent to the National Transportation Safety Board Office of Research and Engineering for data extraction. The data revealed the entire flight and accident sequence. The airplane departed from runway 26 at Sierra Vista, and initiated a climbing right turn to the north-northwest, to a GPS altitude of 8,700 feet. The airplane continued for the next 45 minutes, cruising at a groundspeed of about 158 knots. For the next 75 minutes, the airplane followed a northerly track through the Grand Canyon region at altitudes varying between 10,800 and 12,750 feet. After crossing the Utah border, the airplane leveled off at 12,750 feet on a north-northeast heading, where it continued for the next 75 minutes, traveling at a groundspeed of about 145 knots. At 1206, having reached the southern shores of Utah Lake, 45 miles southwest of South Valley Airport, the airplane initiated a descent. The airplane maintained an airspeed of about 160 knots throughout the descent, until it reached an altitude of 5,890 feet (1,240 feet above ground level), 3.5 miles south of the departure end of runway 34. The airplane was receiving visual flight rules (VFR) flight following throughout the entire flight, and the pilot had been given a clearance to descend through class B airspace as he approached the Salt Lake City area. At 1820, air traffic control personnel reported that he had left class B airspace, clearing him to change to the South Valley Airport common traffic advisory frequency (CTAF), and squawk VFR. An audio recording of the South Valley Airport CTAF revealed a radio transmission made by the pilot reporting that he was, “on the downwind entry for runway 16”. Twenty-six seconds later, an indiscernible distress transmission was made over the frequency. Witnesses positioned at vantage points about 1 mile southeast of the departure end of runway 34, observed an airplane performing a spiral, nose-down dive, at altitudes ranging from between 300 and 500 feet agl. Some witnesses reported observing the airplane transition from a spiraling descent, to a spin, as it fell beyond their view. GPS data revealed that about that location, the airplane was traveling northbound at a groundspeed of 106 knots, and an elevation of 1,000 feet agl. Three seconds later, the airplane had begun a 15-degree turn to the left, remaining at the same altitude, at a groundspeed of 95 knots. Over the next 9 seconds, the airplane had completed a 360-degree left turn, with the last recorded position at 180 feet agl, and a groundspeed of 52 knots. The wreckage was located about 150 feet to the west of the last GPS location. PERSONNEL INFORMATION A review of FAA airman records revealed that the 60-year-old pilot held a private pilot certificate with ratings for airplane single-engine land issued on August 27, 2004. He held a third-class medical certificate issued in November 2009, with the limitation that he must wear corrective lenses for near and distant vision. An examination of the pilot's logbook revealed a total flight experience of 978.6 hours since his first training flight in September 2003, through to his last logbook entry dated September 9, 2010. He had amassed a total of about 810 flight hours in the accident airplane since April 2005. The pilot completed a flight review in accordance with FAR 61.56 on September 25, 2010. No logbook entries were located indicating the pilot had prior experience flying into South Valley Airport. AIRCRAFT INFORMATION The low-wing, two-seat airplane was equipped with a four-cylinder Lycoming engine, serial number L-45210-27A. No data plate was located on the engine, and this information was garnered from the serial number stamped into the upper tab of the crankcase. Lycoming records indicated that the engine was originally manufactured in 1976, and was of the O-320-E2D series. The engine was equipped with an Ellison Fluid Systems EFS-4 throttle body injector, in lieu of a carburetor. Ignition was provided by a single Slick 4371 series magneto, and a Lightspeed Engineering, Plasma I Ignition system. The fixed-pitch propeller was a 70CM6 series, manufactured by Sensenich. FAA records indicated that the airplane was issued its special airworthiness certificate, in June 2000. The pilot purchased the airplane in April 2005. Maintenance records revealed that the airplane had undergone a conditional inspection on April 14, 2011, at a total time of 1,052.5 flight hours. The total flight time of the engine, which had been installed at the time of the original airworthiness certificate issuance, could not be determined. Damage to the instrument panel precluded a determination of the total airframe flight hours at the time of the accident. The airplane was not equipped with a supplemental oxygen system. METEOROLOGICAL INFORMATION The closest aviation weather observation station was located at Salt Lake City International Airport (SLC), 10 miles north of the accident site. The elevation of the weather observation station was 4,227 feet mean sea level (msl). An aviation routine weather report (METAR) was recorded at 1153. It reported: winds from 180 degrees at 9 knots; visibility 10 miles; few clouds 7,500 feet; temperature 22 degrees C; dew point 08 degrees C; altimeter 30.01 inches of mercury. Towering cumulus clouds observed distant northeast, southeast, and southwest. AIRPORT INFORMATION South Valley Regional Airport is at an elevation of 4,606 feet. The airport is positioned below Salt Lake City class B airspace, within a notched lower shelf, the ceiling of which is 6,000 feet msl. The airport is centered about 1-mile west of the central core of the class B airspace, which extends from the surface to 10,000 feet msl. The airport is not equipped with a control tower, and has one active runway (16/34), which is 5,862-foot-long, and 100-foot-wide. An abandoned 3,500-foot-long, 15-foot-wide runway, oriented on a heading of about 305 degrees magnetic is positioned on the east side of the airport, and intersects the approach end of runway 16. Runway 16 utilizes a right-hand traffic pattern flow, and a traffic pattern altitude of 800 feet. WRECKAGE AND IMPACT INFORMATION The airplane wreckage was located 4,800 feet east of the approach end of runway 34. The entire aircraft structure was located on the concrete surface of a sidewalk, at the entrance to a school, 5 feet from the main building structure. No witness marks or damage was noted to any of the school structure, or surrounding trees and lampposts. The airplane remained upright and intact on a heading of about 110 degrees magnetic. Extensive fragmentation and crush damage was observed from the firewall through to the aft cabin. Both wings remained attached to the center cabin through the main spar. The wings exhibited similar leading edge crush damage along their entire length, with a crush angle of about 30 degrees relative to the chord. The empennage section remained intact, and sustained minimal damage. All control surfaces were accounted for at the acci