WPR17FA171

The pilot's exceedance of the airplane's critical angle of attack during takeoff in high density altitude conditions, which resulted in an aerodynamic stall, loss of control, and subsequent impact with terrain.

The commercial pilot and passenger departed in the airplane from the airport, which was located at an elevation of 6,752 ft mean sea level (msl). Airport surveillance video showed that the airplane became increasingly slow during the initial climb after takeoff. A witness reported that, as the airplane approached the end of the runway, it stopped climbing and entered a nose-high pitch attitude that the witness described as "hanging by the prop." The airplane then turned 90° to the downwind leg of the airport traffic pattern and sank as the wings rocked back and forth before it disappeared behind trees. The wreckage orientation indicated that the airplane maintained a southerly heading before it descended into the tree line. The airplane impacted the ground in a nose-down attitude with partial forward bending of the tail, consistent with an aerodynamic stall. Postaccident examination of the airplane did not reveal any preimpact anomalies. The density altitude about the time of the accident exceeded 9,100 ft msl. The effects of high density altitude conditions on takeoff performance include increased takeoff roll distance and reduced rate of climb. Review of performance charts indicated that the airplane should have been able to climb at a rate around 440 ft per minute; however, the video indicated that the airplane was climbing at a rate of 340 ft per minute. It is likely that, experiencing degraded airplane performance due to the density altitude, the pilot responded by increasing the airplane's pitch attitude in an attempt to improve its rate of climb. The pilot subsequently exceeded the airplane's critical angle of attack, which resulted in an aerodynamic stall and impact with terrain. The pilot's primary flight experience was in turbine engine-equipped rotorcraft, and he had recently received a checkout in the accident airplane make and model that included high density altitude operation and mixture leaning procedures. The airplane's mixture control was found in the full rich position after the accident; however, the position of the control before and during the takeoff could not be determined. If the pilot departed in the high density altitude environment without leaning the fuel/air mixture control or subsequently enrichened the fuel/air mixture control to troubleshoot the airplane's reduced takeoff performance, this would have further reduced the available engine power and the airplane's climb rate.

The 1615 recorded weather observation at L35 included wind from 090° at 7 knots, 10 statute miles visibility, scattered clouds at 8,500 ft, temperature 25°C (77° F), dew point 5°C (41° F), and an altimeter setting of 30.33 inches of mercury. An NTSB weather study showed a density altitude of 9,138.9 ft msl about the time of the accident. The pressure altitude at the time of the accident was 6,362.2 ft. The pilot, age 30, held a commercial pilot certificate with ratings for airplane single- and multi-engine land and instrument airplane. He also held ratings for rotorcraft-helicopter and instrument helicopter. The pilot's most recent Federal Aviation Administration (FAA) first-class medical certificate was issued on April 12, 2017, with no limitations. At the time of the exam, the pilot reported that he had accumulated 225 total hours of flight experience, with 0 hours in the previous 6 months. According to his personal logbook , which was current as of July 10, 2017, the pilot accumulated a total of 225 total hours of flight experience. Most of the pilot's single-engine flight time was accrued in a Diamond DA-40 airplane. His logbook indicated that he had completed a total of three flights and accrued 13 hours of flight experience in the accident airplane make and model. The pilot also flew the UH-60 Black Hawk, a military rotorcraft equipped with twin turbine engines; this flight experience was not included in his personal logbook. The pilot's personal logbook showed that he had previously flown to L35 in a Cessna 172 on May 10, 2017. This was his only prior flight to the high-altitude airport. On May 1, 2017, the pilot received a checkout in a Cessna 172 owned by the flight school that owned and operated the accident airplane. According to the instructor who completed the checkout, the local flight included standard practice maneuvers such as slow flight and steep turns, and reviewed fuel/air mixture control leaning procedures, since the pilot was not as experienced in operating reciprocating engines as he was with turbine engines. The flight school's standard practice was to review mixture control leaning, since APV is located at an elevation about 3,000 ft mean sea level (msl) and the temperature is typically warmer than international standard atmosphere. The airplane came to rest in a wooded area about 0.5 nautical miles south of L35. The initial impact point (IIP) was identified by a tree scar near the top of a 45-ft-tall tree and the left wingtip, which was co-located with the tree. An additional scar was found on another tree about 20 ft forward of the initial tree strike signature. The right elevator remained attached to its horizontal stabilizer and was located 20 ft forward of the second tree. The main wreckage, which was oriented on a 085° heading and marked by multiple broken tree branches, was positioned in a 40° nose-down angle about 40 ft past the IIP heading of 227° and comprised the engine, fuselage, wings, and empennage. The right wing was displaced forward a few degrees relative to the fuselage and displayed a depression at the leading edge adjacent to the wing root. A cluster of dents was observed near the outboard leading edge. The left aileron exhibited buckling and compression and the flap displayed some compression wrinkles. Tree impact signatures were located throughout the right wing. Multiple dents and compression wrinkles were found on the upper and lower right wing skins. The left wing separated from the wing root and exhibited an approximate 10-inch depression at the outboard leading edge. Aft bending was observed at the outboard portion of the wing's leading edge and aft compression was found at the inboard leading edge portion of the wing. The fuselage was intact with the exception of the engine, which had separated from the engine firewall. The vertical stabilizer, rudder, and left horizontal stabilizer were secured to the empennage, which remained attached to the aft fuselage. The right horizontal stabilizer separated at the stabilizer root, came to rest in the wreckage path, and displayed a depression at the leading edge consistent with tree impact. The rudder, aileron, and elevator cables were traced from the cockpit to their respective control surfaces. Both the flap indicator and flap handle indicated that the flaps were extended 10°; however, the flap jackscrew did not display any threads, consistent with a flaps-retracted position. The throttle was broken and the mixture control knob was in the full rich position. Both wing fuel tanks were breached and contained an odor consistent with 100 low lead aviation grade gasoline. Fuel line continuity was confirmed from the wing fuel lines to the engine through the fuel selector valve, which rotated normally through each detent. The fuel gascolator bowl was removed and contained traces of foreign debris. Rotational continuity was established throughout the engine and valve train when the engine crankshaft was manually rotated using a hand tool. Thumb compression and suction were obtained for all four cylinders. The engine was disassembled and the cylinder combustion chambers and barrels were examined visually; the cylinder bores, valve heads, and piston faces displayed normal operation and combustion signatures. The cylinder overhead components, including the valves, springs, push rods, and rocker arms, exhibited normal operation and lubrication signatures. An examination of the top and bottom spark plugs revealed signatures consistent with normal wear. The oil filter did not display any metallic particles and the oil sump did not contain any metallic particles. The carburetor throttle linkage remained attached to the throttle arm and the mixture linkage remained attached to the throttle plate. Trace amounts of fuel was observed in the plunger within the float valve chamber. The internal components appeared normal, including both the needle valve carburetor floats, which were normal in appearance. The engine was equipped with a single-drive dual magneto, which rotated normally by hand, but did not seat during each turn. Spark was observed at each of the eight ignition harness leads when the unit was manually actuated by hand. The two-blade, ground adjustable propeller was attached to the propeller flange. Both blades exhibited chordwise scratches. One blade displayed forward bending and the other blade displayed tip curling. A complete report of the examination is available in the public docket associated with this case. According to Federal Aviation Administration (FAA) records, the airplane was manufactured in 1980 and was powered by a Lycoming O-320-H2AD, 160-horsepower, air cooled, reciprocating engine. A review of the logbooks revealed that the airplane had accrued about 54 flight hours since its most recent 100-hour inspection, which was completed on July 2, 2017, at 4,252.6 hours total time in service. At the time of the accident, the engine had accrued about 643 total hours since its most recent overhaul, which was completed on October 23, 2015. The airplane had accrued 4,306.4 hours total time in service at the time of the accident. The engine records showed that the engine was removed and reinstalled in 2016; the records stated the replacement was due to "camlobe and no. 3 cylinder." The logbook entry did not show the discrepancies with the camshaft lobe and No. 3 cylinder. The No. 3 cylinder was replaced during the airplane's most recent 100-hour inspection. A fuel receipt recovered from an airport fueler showed that the pilot purchased 5.14 gallons of 100LL aviation gasoline at 1406 on the day of the accident. According to the airport staff, no fuel contamination or engine anomalies were reported by other customers who fueled their airplanes on the day of the accident. On July 29, 2017, about 1420 Pacific daylight time, a Cessna 172N airplane, N5381J, was substantially damaged after it collide