Show Low, AZ, USA
N5532R
CESSNA 172F
The pilot and passenger were departing on a personal flight. Witnesses observed the airplane attempt to take off, but the takeoff was aborted, and the airplane was then taxied back to the approach end of the runway so that the pilot could perform an engine run-up. The witnesses stated that the engine was “sputtering” and “sounded bad” during the takeoff and the taxi to the run up area. The pilot subsequently attempted a second takeoff. The airplane remained at a low altitude, began a left turn toward the downwind pattern, and then “sank” out of sight behind a ridgeline before impacting terrain. A pilot witness stated that the pilot had “milked it [off the runway], set it back down, and then milked it off [the runway] again.” This witness also described the engine as “running rich, like it was bogged down” during the second takeoff. Postaccident examination of the engine found that the No. 4 engine cylinder exhaust valve was stuck due to a buildup of material that enlarged the overall diameter of the valve’s stem. Examination of the valve stem deposits showed indications of an organic compound that was consistent with deposits of unburned fuel. The stuck valve led to a partial loss of power during the accident takeoffs. The accident pilot reported to another pilot that there had been previous engine problems that had been identified as stuck valves. The accident pilot also reported that he ”never leaned the engine” and that he had little to-no training on how to lean the engine. The partial loss of engine power that resulted from the No. 4 cylinder exhaust valve becoming stuck was likely due to the pilot's improper leaning of the engine over an extended period. Excessively rich mixtures can lead to a buildup of unburned hydrocarbons, which can foul engine components with deposits. The accident could likely have been avoided if the pilot had the airplane examined by maintenance personnel before attempting the second takeoff.
HISTORY OF FLIGHTOn May 25, 2022, about 1750 mountain standard time, a Cessna 172F airplane, N5532R, was substantially damaged when it was involved in an accident near Show Low Regional Airport (SOW), Show Low, Arizona. The pilot and passenger were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. On the morning of the accident, the pilot flew from Ak-Chin Regional Airport (A39), Maricopa, Arizona, to Falcon Field Airport (FFZ), Mesa, Arizona, to pick up the passenger and then departed for SOW. The flight arrived at SOW about 0900, and the airplane occupants spent most of the day away from the airport. A witness stated the pilot and passenger returned to the airport in the late afternoon. The witness assisted them with refueling the airplane at the self-service fuel pump and stated that both wing tanks were filled to the bottom of the filler neck. Witnesses at SOW observed the airplane attempt to take off from runway 25 about 1745. The airplane became airborne two or three times during the first attempted takeoff but did not climb very high. One witness stated that the airplane touched down, “got squirrely,” and almost departed the end of the runway. Another witness stated that the airplane slid sideways and that the engine “did not sound healthy.” Another witness stated that the engine was “sputtering.” The pilot then taxied the airplane back to the approach end of runway 25 and performed a run-up. A witness stated the engine “sounded bad” when the airplane was taxiing. The pilot then attempted a second takeoff. According to a witness who was also a pilot, the accident pilot “milked it off [the runway], set it back down, and then milked it off [the runway] again.” The witness stated that the engine was “running rich, bogged down” during the second takeoff. The airplane remained at a low altitude, began a left turn toward the downwind pattern, and then “sank.” Another witness stated that, during the left turn, the airplane descended out of sight behind a ridgeline. The airplane subsequently impacted terrain in an open field about 1 mile southwest of the departure end of runway 25. AIRCRAFT INFORMATIONThe engine was overhauled on April 29, 2016, and six new Continental 658319A1 cylinders were installed. On October 28, 2020, the pilot purchased the accident airplane. On April 26, 2021, the No. 2 cylinder was removed due to a stuck exhaust valve. The work order for the cylinder repair did not specify a reason for the stuck valve. The valve was repaired, and the cylinder was reinstalled 4 days later. At that time, the engine had accumulated 169.32 hours of tachometer time. The engine logbook contained entries for an annual inspection on September 29, 2021, and an oil change on February 19, 2022. The tachometer displayed 276.79 hours at the time of the accident. The pilot’s supervisor, who was also a pilot and had flown with the accident pilot, thought an exhaust valve also became stuck sometime between January 16 and February 27, 2022, and that the pilot had difficulty finding a mechanic to fix the stuck valve. The supervisor further stated that he explained to the pilot the procedure for resolving the stuck valve, but he did not know if the pilot attempted that procedure himself or found a mechanic to perform the work. The pilot’s supervisor also stated that, during one flight with the accident pilot, he (the supervisor) was leaning the engine when the pilot stated that he “never leaned the engine” and “didn’t need to lean the engine below 3000 feet.” The pilot indicated that he had “little or no training” on leaning the engine. AIRPORT INFORMATIONThe engine was overhauled on April 29, 2016, and six new Continental 658319A1 cylinders were installed. On October 28, 2020, the pilot purchased the accident airplane. On April 26, 2021, the No. 2 cylinder was removed due to a stuck exhaust valve. The work order for the cylinder repair did not specify a reason for the stuck valve. The valve was repaired, and the cylinder was reinstalled 4 days later. At that time, the engine had accumulated 169.32 hours of tachometer time. The engine logbook contained entries for an annual inspection on September 29, 2021, and an oil change on February 19, 2022. The tachometer displayed 276.79 hours at the time of the accident. The pilot’s supervisor, who was also a pilot and had flown with the accident pilot, thought an exhaust valve also became stuck sometime between January 16 and February 27, 2022, and that the pilot had difficulty finding a mechanic to fix the stuck valve. The supervisor further stated that he explained to the pilot the procedure for resolving the stuck valve, but he did not know if the pilot attempted that procedure himself or found a mechanic to perform the work. The pilot’s supervisor also stated that, during one flight with the accident pilot, he (the supervisor) was leaning the engine when the pilot stated that he “never leaned the engine” and “didn’t need to lean the engine below 3000 feet.” The pilot indicated that he had “little or no training” on leaning the engine. WRECKAGE AND IMPACT INFORMATIONThe airplane impacted the edge of a stream in an open field. The wreckage was oriented along a 075° heading. The accident site and debris field were confined to the initial impact point. Forward of the empennage, the fuselage was bent downward. All flight control surfaces were attached to the airplane, and flight control continuity was established to the cockpit controls. The engine was pushed aft, and it protruded into the cockpit. The engine remained attached to the airframe. Engine control continuity was not established due to impact damage. The carburetor was impact separated from the engine. The mixture control at the carburetor was observed in the lean position. Valve train continuity and thumb compression/suction were obtained on all cylinders except for cylinder No. 4. Cylinder No. 4 was removed, and the exhaust valve was observed to be stuck in the open position. The magneto leads for the bottom spark plugs of cylinders Nos. 2, 4, and 6 exhibited impact damage. Both magnetos were removed, and the magneto leads were cut near the housing. The removed magnetos were rotated by hand, and spark was observed on all the leads. The bottom spark plug of cylinder No. 4 exhibited carbon buildup (see figure 1), and the cylinder contained debris (see figure 2). Figure 1. No. 4 cylinder lower spark plug (Source: Textron Aviation). Figure 2. No. 4 cylinder interior and debris (Source: Textron Aviation). The No. 4 cylinder was disassembled, and the exhaust valve stem was mostly covered in carbon buildup (see figure 3). The cylinder and associated exhaust valve components were sent to the National Transportation Safety Board (NTSB) Materials Laboratory for further examination. Figure 3. No. 4 cylinder exhaust valve. Visual examination of the exhaust valve stem found that the 0.6 to 0.7 inches of the exhaust valve stem (from the seat) exhibited deposits and that the deposits that were 0.5 inches from the seat exhibited a dark brown color with a dull luster. The other 0.1 to 0.2 inches of deposits exhibited a black color that was more reflective. Dark brown and orange-yellow deposits were present over the exhaust valve head. The deposits exhibited a flaky layered morphology that increased the overall diameter of the stem (see figure 4). Figure 4. Exhaust valve deposits. The deposits on the exhaust valve stem and valve seat surface were further examined. They showed indications of a single-chained polymer-like organic compound, consistent with deposits of unburned fuel.
The pilot’s improper leaning of the engine during an extended period of time, which caused an exhaust valve to become stuck and led to the partial loss of engine power during the accident flight. Contributing to the accident was the pilot’s decision to attempt a second takeoff without having the engine further examined.
Source: NTSB Aviation Accident Database
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