History of Flight
On July 28, 2016, about 0821 central daylight time, a Flight Design GMBH model CTLS airplane, N527TS, impacted terrain after a loss of engine power following takeoff. The private pilot was fatally injured, and the passenger was seriously injured; the airplane sustained substantial damage. The flight was conducted under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Fond du Lac County Airport (FLD) in Fond du Lac, Wisconsin, and its intended destination was not determined.
Witnesses reported seeing the airplane take off from runway 36 and then turn left back toward the runway while still over airport property. The engine sounded abnormal to them. One witness stated that the airplane did not climb above treetop height before it rolled into a steep left turn and descended into terrain. Another witness did not see the accident but heard the pilot state on the radio that he was making an immediate return to the airport. The terrain beginning about 0.2 miles north of the runway consisted of commercial properties and parking lots that were not suitable for landing.
Personnel Information
No pilot logbooks were located during the investigation, and the pilot's time in the accident airplane make and model could not be determined. On his last application for a medical certificate dated April 15, 2002, the pilot reported 110 total hours. He did not hold a current FAA medical certificate, but he was not required to hold one to operate the light-sport airplane.
The pilot-rated passenger's logbooks were also not found. On his last medical certificate application dated July 15, 1996, he reported 2,136 total hours.
Aircraft Information
A review of the airplane's maintenance records showed that a 200-hour carburetor service requirement per Rotax Aircraft Engines Service Instruction (SI)-912-021, "Inspections of Carburetors," was performed on December 9, 2014. The Hobbs meter read 829.5 hours at that time. At the time of the accident, the Hobbs meter read 960.5 hours.
Wreckage and Impact Information
The wreckage was located 0.15 miles northwest of the departure end of runway 36 at FLD. Examination revealed that both wings had separated from the fuselage, and the engine had intruded into the cockpit area. Flight control continuity to the elevator and rudder was confirmed from the cockpit to each control surface. Continuity was interrupted to both ailerons, but all observed breaks were consistent with overload failure during impact. A slight fuel smell was present at the scene. Both fuel tanks were compromised. Several ounces of liquid consistent with aviation fuel, appearing light blue and free of contaminants, were recovered from the right-wing fuel tank. The three composite propeller blades were broken and separated near the hub; the blade sections lacked chord-wise scratches or leading-edge damage.
Additional Information
Rotax Aircraft Engines issued SI-912-021 on November 9, 2009. The service instruction called for carburetor inspection after engine installation, initial operation, return to service, when the engine runs rough, or at the next scheduled maintenance event. It warned that non-compliance could result in engine damage, personal injury, or death. It noted that several carburetors had been found with contamination in the float chamber, including dirt, rubber residue, Loctite, resin-like substances, and sediments, which could cause partial or complete blockage of jets or other vital ducts, leading to poor performance or engine stoppage. Possible shortcomings in the fuel system included dirt, missing or unsuitable fuel filters, clogged filters, unsuitable fuel lines, dirt in fuel manifold, poor float chamber venting, insufficient flushing, improper fuel pressure, unsuitable tanks and coatings, and contamination from corrosion.
The Rotax 912ULS engine maintenance manual specified removal and assembly of both carburetors every 200 hours.
Medical and Pathological Information
The pilot initially survived the accident but died 12 days later. An autopsy authorized by the Fond du Lac County Medical Examiner's Office attributed the cause of death to multiple injuries sustained in the airplane accident. Forensic toxicology was not performed.
Tests and Research
The engine was examined on August 17, 2016, with the NTSB investigator-in-charge present. The engine remained attached to its mount. The exhaust system was damaged, and the muffler was not attached. No anomalies were noted with the ignition system. The fuel pump was removed and hand-actuated; liquid consistent with aviation fuel was contained within and squirted out when actuated. The oil cooler was detached and impact-damaged. The engine had a non-approved aftermarket oil filter, which was cut open and inspected for ferrous material with no anomalies found. Cylinders and cylinder heads showed no anomalies. The engine was hand-rotated with continuity verified and no anomalies noted. The radiator was impact-damaged. The air filtration system was not available for examination.
The engine was equipped with two carburetors: one fed cylinders 1 and 3, the other fed cylinders 2 and 4. Both carburetors' float bowls were removed. Flaking was noted on the floats, and contamination and corrosion were found on the bottom of the float bowls. Each carburetor's main jets were clear of obstructions, and no fuel was found within the carburetors. The 2/4 carburetor's piston slide was stuck in the idle position within its bore due to contamination. The piston was removed, and contamination was found in the bore preventing sliding. Both carburetors were sent to the NTSB Materials Laboratory for further examination.
Four black floats, two per bowl, moved freely on their posts. Each float was weighed and submerged for 12 hours in automotive gasoline. After soaking, each float had a weight gain of less than 1%. The total combined weight for floats in the 1/3 carburetor was 5.668 grams, and for the 2/4 carburetor 5.674 grams, both below the maximum allowable 7 grams per the BRP-Powertrain Maintenance Manual.
Interior surfaces of the bowls had black areas, white film, and accumulations of white and yellow corrosion products. The black areas were mostly circular on lower surfaces. White film was present on lower surfaces and sides, with thicker white accumulations in some areas that were powdery when disturbed, revealing black underlying surfaces. Yellow accumulations were crystalline and broke into chunks under pressure; the underlying surface was black. Samples of white and yellow accumulations were analyzed. Both had large peaks of zinc and oxygen, consistent with oxides from the cast zinc bowl. Smaller peaks of sulfur and lead were present. The yellow sample and some white areas also showed aluminum, and the yellow sample showed iron, potassium, and higher carbon, with some areas showing silicon.
During laboratory examination, the piston slide from the 2/4 carburetor was reinserted, springs and covers were put in place on both carburetors, and the piston slides were moved up and down. The 1/3 carburetor's piston slide moved relatively easily, while the 2/4 carburetor's piston slide tended to stick. The piston slides were removed and manipulated again, with the 2/4 slide continuing to stick compared to the 1/3. White material accumulations of varying thickness were noted on the interior surfaces of both piston bores. The white material on the 1/3 carburetor bore appeared more evenly distributed than that on the 2/4 bore. A sample of the white material from the 2/4 piston bore was examined and showed high peaks of aluminum and oxygen, consistent with oxidation from the aluminum alloy carburetor cover.