WPR14LA232

A loss of engine power for reasons that could not be determined due to insufficient evidence.

The pilot departed on the cross-country flight with a planned touch-and-go landing at an intermediate airport about 8 miles from the origination airport. The pilot reported that he applied carburetor heat for the approach and landing at the intermediate airport. After touchdown, in accordance with the operating procedures, the pilot retracted the flaps, shut off the carburetor heat, and applied full throttle for the takeoff and climbout. The engine began to lose power when the airplane had gained about 350 ft; the pilot reported that the low altitude prevented him from conducting any emergency procedures except to select an emergency landing location in a field. He did not apply carburetor heat or extend the flaps. The airplane struck a berm in the field, which caused it to nose over inverted and resulted in substantial damage. A postaccident examination of the engine initially revealed incomplete valve seating in one of the forward-most cylinders. Once the valves were staked, the valve seating was normal, so the initial abnormality was attributed to impact. The engine examination did not reveal any evidence of preimpact mechanical anomalies or deficiencies that would have resulted in the loss of power. Although carburetor icing envelope charts indicated the possibility of carburetor icing at glide power, the pilot's use of carburetor heat on the approach, the loss of power with the throttle set at takeoff power, and the ambient conditions were all consistent with a low likelihood of carburetor icing. Because detailed postaccident examination was limited to the engine, the investigation was unable to eliminate the possibility that an airframe or carburetor fuel delivery problem or water contamination of the fuel resulted in the engine power loss.

7S0 was equipped with a single paved runway designated 16/34, which measured 4,800 by 75 feet. Airport elevation was 3,086 feet above mean sea level. 7S0 was located about 8 miles from 8S1. Airplane Manufacturer's Procedural Guidance According to the airplane manufacturer's published operating procedures, the before takeoff procedures included verification of proper operation of the carburetor heat, and a magneto operation check. Proper carburetor heat operation would be indicated by an rpm drop when the carburetor heat was applied. Proper magneto operation would be indicated by the engine continuing to run smoothly on either magneto, plus no more than a 75 rpm differential between operation on either magneto. The manufacturer specified that carburetor heat was to be "cold" (in the off position) for takeoff. The before landing procedures specified that "full" carburetor heat was to be applied "before closing throttle." The guidance specified that in the event of an uncommanded rpm/power reduction in flight, full carburetor heat was to be applied. The pilot stated that engine start, taxi out, and engine run up were all normal. The carburetor heat operated normally, with an observed rpm decrease. The engine ran smoothly on each magneto, with the respective rpm decreases within limits. Carburetor Icing FAA Advisory Circular AC 20-113, regarding induction system icing, discussed two components of carburetor icing; throttle ice and fuel vaporization ice. The AC stated that "Throttle ice is usually formed at or near a partially closed throttle, typical of an off-idle or cruise power setting, " and "occurs when water vapor... freezes because of the cooling restriction caused by the carburetor venturi and the throttle butterfly valve." The AC stated that fuel vaporization ice "usually occurs in conjunction with throttle icing. It is most prevalent with conventional float type carburetors." The AC stated that "vaporization icing may occur at temperatures from 32 degrees F to as high as 100 degrees F, with a relative humidity of 50 percent or above." Carburetor icing prevention procedures advanced by the AC included maintenance checks, and preflight operational checks by the pilot. The AC stated that pilots should conduct takeoffs without carburetor heat, "unless extreme intake icing conditions are present." The AC noted that carburetor icing "is more likely" when relative humidity is above 80 percent. Siting of the ambient conditions on one FAA carburetor icing envelope chart indicated that the conditions were near the center of the "Serious Icing (glide power)" region, and near the lower edge of the region labeled "Carburetor Icing Possible" on another FAA carburetor icing envelope chart. Water Contamination of Fuel Water contamination of fuel can adversely affect engine operation, and can result in a partial or complete loss of power. Over time, if water is present in the fuel, it will precipitate out, and settle at the lowest point(s) in the fuel tank or system. The airplane was equipped with fuel tank sump drains to permit the pilot to check the fuel for water contamination, and remove it from the tanks. The airplane was also equipped with a fuel strainer which, within limits, separates the water from the fuel and thereby prevents water from being introduced into the carburetor. The pilot stated that prior to the flight he drained the sumps and strainer, and did not detect any water in the fuel. The propeller, engine, cowling, and nose gear were all damaged and displaced aft by the impact. The fuselage was wrinkled in several locations aft of the main landing gear. The vertical fin and a portion of the rudder were also deformed. Photographs taken shortly after the accident, while the airplane was still inverted in the field, indicated that the flaps were in the retracted position. According to an FAA inspector, the owner informed him that the airplane had departed on the flight with full fuel tanks. The airplane owner was advised by the NTSB that he could recover the airplane, but that only the FAA and/or an NTSB-approved mechanic were permitted to conduct any maintenance or investigative activities on the airplane. The owner agreed, and there was no evidence that the owner or any other persons tampered with the airplane after its recovery. On June 17, 2014, an FAA inspector and an aircraft mechanic examined the airplane. That examination did not detect any indications of non-impact related distress or failures. The lower engine mounts were fractured. The fuel line was fracture-separated from the fuel strainer, but the condition or contents of the fuel strainer were not otherwise noted. No airframe fuel system checks were conducted. The carburetor linkage and air box were deformed consistent with impact, which prevented movement of the throttle, mixture, and carburetor heat controls. The carburetor heat control was found lodged in the off (no carburetor heat) position. The throttle and mixture controls were found lodged in their full throttle and full rich positions, respectively. No additional checks of carburetor condition, integrity, or functionality were accomplished. Cold compression checks of the cylinders revealed that three cylinders were unremarkable, but that the initial check on the No. 3 cylinder resulted in a reading of 18/80, with significant leakage past both the intake and exhaust valves. The mechanic staked both valves, and then obtained a normal reading. The reasons for the initial low pressure reading, or the success of the staking, with its implication that the valves were initially not completely sealed on their seats, were not determined, or investigated further, by the inspector or the mechanic. All eight spark plugs were removed and examined; their electrodes exhibited varying states of wear, plus carbon or oil deposits. The electrodes of the four spark plugs from the Nos. 1 and 2 (aft) cylinders were noticeably cleaner and lighter in color than those from the Nos. 3 and 4 (forward) cylinders, which was consistent with the aft cylinders operating at a leaner mixture than the forward cylinders. However, all electrodes were consistent with the range of appearances associated with normal service. The mechanic reported that the No. 2 top spark plug "looked like it was not firing." The appearance of that spark plug was very clean, consistent with the Champion "Aviation Check-a-Plug" normal condition. A lack of empirical industry data and guidance regarding the appearance of non-firing spark plugs prevented a conclusion based solely on appearance. A non-firing spark plug would manifest itself as noticeable engine roughness during an engine run up magneto check, and the pilot did not report any such roughness. The magneto switch tested satisfactorily at all selection positions. The magneto to engine timing for both magnetos was found to be 25 degrees before top dead center (BTDC). The Continental Motors specified setting was 24 degrees BTDC, with a tolerance of plus or minus 1 degree. Impact damage precluded functional testing of the magnetos. The rocker covers were removed, and all visible valve train components were observed to be intact, and to operate properly with engine rotation. The interiors of all cylinders were examined, and were unremarkable. No contact marks from any valves were observed on the piston heads. The damage to the carburetor airbox, combined with the inability to test run the engine, prevented the determination of the pre-impact functionality and performance of the carburetor heat system. The 1321 non-certified weather observation for Ronan included wind from the south-southeast at 2 knots, temperature 20 degrees C, dew point 10 degrees C, and a barometric pressure of 29.97 inches of mercury. The calculated relative humidity was 53 percent. The 18-year-old pilot held a private pilot certificate with an airplane single-engine land rating. He reported that he