WPR17LA175

The partial loss of engine power during initial climb due to the No. 3 cylinder exhaust valve becoming stuck open due to deposit buildup in the exhaust valve stem and guide and the pilot’s exceedance of the airplane’s critical angle of attack while attempting to turn back to the airport, which resulted in an aerodynamic stall.

Shortly after the private pilot took off for the local flight, about 200 to 300 ft above ground level, the engine experienced a partial loss of power. The airport was bordered on the south, west, and north by buildings, and there were high-traffic arterial roads on both the west and south sides of the airport; the pilot turned the airplane back toward the departure runway to make an emergency landing to the east. During the turn, the pilot exceeded the airplane's critical angle of attack, which resulted in an aerodynamic stall. The pilot was unable to regain control, and the airplane pitched nose down and subsequently impacted terrain and then collided with an airport perimeter fence and a tree before coming to rest. Postaccident examination of the propeller blades revealed chordwise striations across the cambered surface, torsional twisting, and trailing edge "S" bending, consistent with the engine producing power at the time of impact. The engine teardown examination revealed that the No. 3 cylinder's exhaust valve was stuck open, which would have degraded the engine power. Further, the exhaust valve stem and guide exhibited heavy combustion deposits, which likely led to the valve becoming stuck. No preaccident deficiencies were found with the cylinder.

At 1253, the DVT weather reporting facility indicated wind from 180° at 4 knots, visibility 10 miles, sky clear, temperature 34° Celsius (C), dew point 16° C, and an altimeter setting of 29.93 inches of mercury. The 18-year-old pilot held a private pilot certificate with a rating for airplane single-engine land. A friend of the pilot reported that the pilot had accumulated about 270 total flight hours, 207 hours as pilot-in-command, and 226 hours which were in the same make and model as the accident airplane. The pilot held an FAA first-class airman medical certificate, which was issued on April 23, 2015, with no limitations reported. A FAA aviation safety inspector, who responded to the accident site shortly after the accident, reported that after impacting the ground the airplane skidded into a tree, then broke at mid-fuselage splitting the airplane body into two pieces, with the cockpit and the fuselage on each side of the tree. The inspector stated that the engine appeared to be producing power, based on observable propeller blade signatures. The blades exhibited chordwise striations across the cambered surface, torsional twisting and trailing edge "S" bending. Additionally, the engine had separated from the airplane and came to rest on the road that borders the airport to the west, about 90 ft south of the main wreckage site. Both the left and right wings had also separated from the fuselage, with the left wing having come to rest about 30 ft northwest of the main wreckage, and the right wing about 180 ft south of the main wreckage site. During a postaccident examination of the fuel selector by the NTSB IIC and a Federal Aviation Administration inspector, the component functioned as designed through all positions. It was observed that a stop pin was sheared off inside of the selector that would have prevented the selector from traveling too far to the left. Photo documentation at the accident site showed that the fuel selector was selected to the left tank position. The left fuel tank had been breached and showed evidence of fuel dispersion; the quantity of the fuel spill was estimated to be between 3 to 5 gallons. The inspector reported that the right wing did not show any evidence of a fuel spill and that no fuel remained in the wing. The inspector opined that the Type Certificate Data Sheet for the AA-1B airplane states that there is 2 gallons of unusable fuel in each wing. The inspector's review of the fuel receipts for the accident airplane revealed that 7.8 gallons of fuel was purchased on July 31 at 2107, and that the accident flight was the first flight since the fuel was added. Engine Examination The engine remained attached to the engine mount and had been liberated from the firewall during the accident/impact sequence. The engine had sustained significant impact energy absorption to the right forward/lower area of the number two cylinder and exhaust system. The attached propeller and flywheel were bent. All engine accessories remained secure at their respective mountings. Visual examination of the engine revealed no external evidence of pre-impact catastrophic mechanical malfunction or fire. The left and right magnetos remained securely clamped at their respective mounting pads. The ignition harness was secure at each magneto. Magneto to engine timing could not be ascertained, due to the flywheel impingement on the engine crankcase. The magnetos were removed for examination. Each magneto produced spark at the end of the respective spark plug lead, during hand rotation of the drive. The drives of each magneto remained intact and undamaged. The propeller and flywheel were removed to facilitate the examination. The top spark plugs were removed, examined and photographed. The rocker covers of each cylinder were removed. The vacuum pump was removed, and the crankshaft was rotated by hand through the drive pad utilizing a drive tool. The crankshaft was free and easy to rotate in both directions. "Thumb" compression was observed in proper order on cylinders 1, 2 and 4. It was noted that the number 3-cylinder exhaust valve was not moving and stuck in the OPEN position. The complete valve train was observed to operate in proper order and appeared to be free of any pre-mishap mechanical malfunction. Normal "lift action" was observed at each rocker assembly and pushrod of the number 3 exhaust valve. Clean, uncontaminated oil was observed at all four rockerbox areas. Mechanical continuity was established throughout the rotating group, valve train and accessory section during hand rotation of the crankshaft. The bottom spark plugs were removed, examined and photographed. The spark plug electrodes remained mechanically undamaged, and according to the Champion Spark Plugs "Check-A-Plug" chart AV-27, the spark plug electrodes displayed coloration consistent with normal operation. The combustion chamber of each cylinder was examined through the spark plug holes utilizing a lighted borescope. The combustion chambers remained mechanically undamaged, and there was no evidence of foreign object ingestion or detonation. The valves were intact and undamaged. There was no evidence of valve to piston face contact observed. The gas path and combustion signatures observed at the spark plugs, combustion chambers and exhaust system components displayed coloration consistent with normal operation. There was no oil residue observed in the exhaust system gas path. The exhaust system was found free of obstructions. The number 3-cylinder was removed to facilitate further examination. The cylinder assembly was properly secured to the crankcase and appeared free of significant impact energy damage. The intake, exhaust rockers and valve train components within the rockerbox area appeared properly lubricated and free of mechanical damage. The intake and exhaust pushrods remained straight and free of damage. The intake pushrod shroud had sustained superficial impact damage. The intake rocker assembly remained undamaged and exhibited no evidence of lubrication depravation. There was no intake rocker pin oil hole. The exhaust rocker assembly remained undamaged and exhibited no evidence of lubrication depravation. The exhaust rocker pin oil hole remained free of obstruction. The number 3-piston was removed from the connecting rod. The piston pin was undamaged and free of heat distress. The piston pin bushing remained secure and exhibited no unusual wear signatures. The number 3-piston exhibited no evidence of valve to piston face contact. The piston skirt exhibited no unusual wear signatures. The ring assemblies at each piston were intact and free to rotate within their respective ring land. The cylinder barrel bore remained free of damage and was absent of any significant heat distress signatures. There was no evidence of foreign object ingestion or detonation. The valves remained intact and undamaged. There was no further disassembly or examination of the subject cylinder. The valve was not moved from the original position it was found in during this examination. The two-seat, low-wing airplane, serial number AA1B-0016, was manufactured in 1972. It was powered by a Lycoming model O-320-A3A, 150-horsepower engine, and equipped with a Sensinich two-blade propeller, model M74DM-0-58. A review of the maintenance logbook records revealed that during the 100-hour inspection that was performed on February 9, 2017, the number 3-cylinder was replaced with a new Millennium cylinder, part number SA 32006N-A21P, at a tach time of 432.4 hours. At the time of the inspection when the number 3-cylinder was checked for compression, it registered 36/80, which prompted the cylinder change. The most recent 100-hour inspection was performed on May 11, 2017, about 125 hours prior to the accident. At this time the number 3-cylinder exhaust gasket was replaced. In conjunction with the inspection, a subsequent ground run revealed no anomalies with the engine. A mai