CEN16FA290

The private pilot departed the airport in the light-sport airplane and made a left turn back toward the airport while still over airport property. The airplane was at a low altitude when it rolled to the left and impacted terrain, consistent with a loss of control following an aerodynamic stall. Witnesses stated that the engine sounded abnormal. One witness reported that the airplane did not climb above treetop height before it rolled into a steep left turn and descended into terrain. An additional witness did not see the accident occur but heard the pilot state on the radio that he was making an immediate return to the airport. The terrain in front of the pilot on departure was commercial properties and parking lots, and was unsuitable for landing. During postaccident examination, contaminants and corrosion were found in both carburetor bowls. The piston slide in the carburetor for the Nos. 2 and 4 cylinders was found stuck in the idle position in its bore on the carburetor chamber top. A white substance was present on the interior surface of the bore that prevented the piston from sliding up and down within the bore. Testing of the substance determined that it was likely contamination produced by oxidation and corrosion of the aluminum alloy carburetor chamber top because of exposure to water-contaminated fuel. The engine manufacturer had previously issued a Service Instruction (SI) that warned of the possibility of poor performance or engine stoppage due to contaminants in the carburetor float chamber. One of the sources of contaminants identified in the SI was corrosion caused by high water content in fuel. Both carburetors had been inspected in accordance with the SI about 130 flight hours and 19 months before the accident, which was within the SI recommended 200-hour inspection interval. The contaminants found in the carburetors were indicative of the use of fuel with high water content at an undetermined time, most likely after compliance with the SI.

Rotax Aircraft Engines issued SI-912-021 on November 9, 2009. The following was extracted from that SI: 1.5) Compliance - After engine installation/initial operation/return to service of an engine. - When engine is running rough. - And/or at the next scheduled maintenance event of carburetor (see Maintenance Manual for engine type 912/914 Series, current issue). WARNING: Non-compliance with these instructions could result in engine damages, personal injuries or death. 3.1) General Several carburetors have been found with contamination (dirt, remains of rubber from fuel lines and Loctite, resin-like substance, sediments etc.) in the float chamber. WARNING: This contamination could possibly cause a partial or complete blockage of the idle or main jet or of other ducts vital for operation, leading to poor performance or stoppage of engine. 3.1.1) Possible shortcomings in the fuel system - Dirt in the fuel system - Missing or unsuitable fuel filter - Clogged fuel filter - Unsuitable fuel lines - Dirt in fuel manifold - Poor float chamber venting - Insufficient flushing of the fuel system prior to initial engine operation - Fuel pressure too low or too high - Unsuitable fuel tanks and tank coatings - Contaminated float chambers (e.g. corrosion caused by high water content in the fuel) 3.1.2) Fuel Use only quality fuel as specified. - EN 228 regular, EN 228 premium, EN 228 Super plus or AVGAS 100LL. NOTE: The exact defined minimum requirements for fuel are specified in the relevant operators manual (for the relevant engine type) and the Service Instructions SI-912-016/SI-914-019 and SI-2ST-008 „Selection of suitable operating fluids", current issue. The Rotax 912ULS engine maintenance manual specifies removal/assembly of both carburetors every 200 hours. A review of the airplane's maintenance records revealed that a 200-hour carburetor service requirement per Rotax Aircraft Engines Service Instruction (SI)-912-021, "Inspections of Carburetors," was complied with on December 9, 2014. According to the records, the Hobbs meter read 829.5 hours at the time of the carburetor inspection. At the time of the accident, the Hobbs meter read 960.5 hours. On July 28, 2016, about 0821 central daylight time, a Flight Design GMBH model CTLS airplane, N527TS, impacted terrain following a loss of engine power after takeoff. The private pilot was fatally injured, and the passenger was seriously injured. The airplane was substantially damaged. The airplane was registered to and operated by the pilot as a 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed at the accident site about the time of the accident, and the flight was operated without a flight plan. The flight was originating from Fond du Lac County Airport (FLD), Fond du Lac, Wisconsin, at the time of the accident, and its destination was not determined. Witnesses reported seeing the airplane take off from runway 36 and turn left back toward the runway while stillover airport property. They added that the engine sounded abnormal. One witness stated that the airplane did not climb above treetop height before it rolled into a steep left turn and descended into terrain. An additional witness did not see the accident occur but heard the pilot state on the radio that he was making an immediate return to the airport. Beginning about 0.2 miles north of the runway, terrain consisted of commercial properties and parking lots that were not suitable for landing. The pilot initially survived the accident but died 12 days later. An autopsy was authorized and conducted on the pilot by the Fond du Lac County Medical Examiner's Office. The cause of death was attributed to multiple injuries sustained in an airplane accident. Forensic toxicology was not performed. Pilot No pilot logbooks were located during the investigation, and the pilot's time in the make and model of the accident airplane could not be determined. The pilot reported 110 total hours on his last application for a medical certificate dated April 15, 2002. The pilot did not hold a current FAA medical certificate, and he was not required to hold one to operate the light-sport airplane. Pilot-Rated Passenger No pilot logbooks belonging to the pilot-rated passenger were located during the investigation. The pilot-rated passenger reported 2,136 total hours on his last application for medical certificate dated July 15, 1996. The engine was examined on August 17, 2016, in the presence of the National Transportation Safety Board investigator-in-charge. When examined, the engine remained attached to the engine mount. The exhaust system was damaged, and the muffler was not attached to the engine. No anomalies were noted with the ignition system. The fuel pump was removed and hand actuated. Liquid consistent in smell and color to aviation fuel was contained within the pump and squirted out when the pump was actuated. The oil cooler was detached and impact damaged. The engine was equipped with a non-approved aftermarket oil filter. The filter was cut open and inspected for ferrous material; no anomalies were noted. No anomalies were noted with the cylinders and cylinder heads. The engine was hand rotated; continuity was verified, and no anomalies were noted. The radiator was impact damaged. The air filtration system was not available for examination. The engine was equipped with two carburetors. One carburetor fed the Nos. 1 and 3 cylinders, and the second carburetor fed the Nos. 2 and 4 cylinders. For purposes of this report, the carburetors will be referred to as the 1/3 carburetor and the 2/4 carburetor. Both carburetors' float bowls were removed. Flaking was noted on the floats, and contamination and corrosion were found on the bottom of float bowls. Each carburetors' main jets were clear of obstructions, and no fuel was found within the carburetors. In addition, the 2/4 carburetor's piston slide was stuck in the idle position within its bore on the carburetorchamber top. The piston was removed from the chamber top, and contamination was found in the bore that prevented the piston from sliding up and down within the bore. Both carburetors were sent to the NTSB Materials Laboratory for further examination. Two black floats were present in each float bowl, and all four floats moved freely on their respective posts. Each float was weighed and subsequently submerged for 12 hours in a covered container of automobile gasoline. After soaking, the floats were removed from the gasoline and weighed again. Each float had a total weight gain of less than 1%. The sum of the weights for the two floats from each carburetor was 5.668 grams for the 1/3 carburetor and 5.674 grams for the 2/4 carburetor. The maximum allowable combined weight for carburetor floats in each carburetor is 7 grams per the BRP-Powertrain Maintenance Manual for the Rotax 912-series engines. The interior surfaces of the bowls had black areas along with areas of white film and other accumulations of white and yellow corrosion products. The black areas were mostly circular in shape and located on the lower surfaces of the bowls. A white film was present in many areas, particularly on the lower surface and side of the bowl for the 1/3 carburetor. Isolated areas with thicker accumulations of white material were observed in some areas. When disturbed with tweezers, the accumulation had a powdery consistency, and the underlying surface of the bowl was black. Some areas had an accumulation of yellow material. When disturbed with tweezers, the accumulation largely maintained its shape but was easily broken into smaller crystalline chunks when pressure was applied. The surface under the yellow accumulation was also colored black. Samples of the white and yellow accumulations were analyzed and both samples had large peaks of zinc and oxygen consistent with oxides associated with the cast zinc bowl. Both samples also showed smaller peaks of sulfur and lead. The yellow sample and areas of the white sample also showed a peak of aluminum. Additionally, the yellow sample showed peaks of iron and potassium and a higher peak of carbon. Some areas of the yellow sample also showed a peak of silicon. During the laboratory examination of the carburetors, the piston slide from the 2/4 carburetor was reinserted; the springs and covers were put into place on both carburetors; and subsequently, both piston slides were moved up and down. It was noted that the piston slide from the 1/3 carburetor moved relatively easily while the piston slide from the 2/4 carburetor tended to stick. The piston slides were removed from the carburetors with the housings and were manipulated again. The piston slide from the 2/4 carburetor continued to tend to stick compared to the piston slide from the 1/3 carburetor. The piston slides were removed from the covers again, and accumulations of white material of varying thickness were noted on the interior surfaces of the piston bores of bothcarburetors. The white material on the interior surface of the bore in the 1/3 carburetor cover appeared to be more evenly distributed around the surface than the material on the interior surface of bore in the 2/4 carburetor cover. A sample of the white material from the piston bore in the 2/4 carburetor cover was removed and examined. The resulting spectrum showed high peaks of aluminum and oxygen, consistent with oxidation from the carburetor cover, which was made of an aluminum alloy. The wreckage was located 0.15 miles northwest of the departure end of runway 36 at FLD. Examination of the wreckage revealed that both wings separated from the fuselage, and the engine intruded into the cockpit area. Flight control continuity to the elevator and rudder was confirmed from the cockpit to each control surface. Flight control continuity was interrupted to both ailerons, but all observed breaks in continuity were consistent with overload failure during impact. A slight fuel smell was present at the accident scene. Both the left and right fuel tanks were compromised. Several ounces of liquid consistent with aviation fuel were recovered from the right-wing fuel tank, which appeared light blue in color and free of contaminants. The three blades of the composite propeller were broken and had separated near the propeller hub. The blade sections that were observed were absent chord-wise scratches or leading-edge damage. The engine was removed from the wreckage and examined separately at a secure location.