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On November 14, 2009, approximately 1215 central standard time, an Augustine David Sonex experimental light sport airplane was substantially damaged when it impacted terrain one mile north of Burnet Municipal Airport – Kate Craddock Field (KBMQ), Burnet, Texas. Visual meteorological conditions prevailed at the time of the accident. The personal flight was being conducted under the provisions of Title 14 Code of Federal Regulations Part 91 without a flight plan. The commercial certificated pilot was fatally injured. The cross-country flight departed Shirley Williams Airport (44TE) Kingsland, Texas, approximately 1145 and was en route to Spicewood Airport (K88R), Spicewood, Texas.
According to a friend of the pilot, they had flown to an Experimental Aircraft Association (EAA) meeting the morning of the accident and were returning to their home airports. The accident pilot reported to his friend that he was “breaking off” to return to K88R and then five minutes later reported that he was having difficulties and was reversing course to land on runway 01 at KBQM. This was the last transmission he heard.
A flight medic on a relocation flight in the area reported hearing the accident pilot transmit that there was “something really wrong with the airplane.” The pilot declared an emergency shortly thereafter.
One witness observed the airplane descending and fairly low in altitude as if it was going to perform a landing in a field. She observed the airplane bank hard to the right and then descend “straight nose down.” Multiple witnesses reported that the airplane cleared the trees and then nosed over, descending in a nose low attitude. The airplane impacted terrain in a nose low attitude between two rows of trees.
The pilot, age 81, held an airline transport pilot certificate with airplane multiengine land and sea ratings, with several type ratings, in addition to a commercial pilot certificate with airplane single-engine land, and glider privileges. He was issued a third class airman medical certificate on December 13, 2005. The certificate contained the limitation “must wear corrective lenses.” The pilot held a valid Class C driver’s license, issued by the Department of Public Safety in Texas, with an expiration date of June 5, 2011.
The pilot’s personal logbook was not located. At the time of application for his last medical certificate, the pilot reported 12,124 hours total time. On the pilot’s application for insurance, dated January 1, 2008, the pilot reported 12,000 hours total time and zero hours in the make and model of the accident airplane. This application illustrated a biannual flight review date of August 22, 2006.
The accident airplane, an Augustine David L Sonex (serial number 332), was issued a special airworthiness certificate on August 21, 2004. It was registered with the Federal Aviation Administration (FAA) on a special airworthiness certificate for experimental amateur-built operations. A Jabiru 3300A engine powered the airplane. The engine was equipped with a two-blade, Sensenich propeller.
The airplane was registered to and operated by the accident pilot, and was maintained under an annual condition inspection program. A review of the maintenance records indicated that a condition inspection had been completed on October 6, 2009, at an airframe total time of 189.9 hours.
The closest official weather observation station was Burnet Municipal Airport – Kate Craddock Field (KBMQ), Burnet, Texas, located one nautical mile (nm) south of the accident site. The elevation of the weather observation station was 1,284 feet mean seas level. The routine aviation weather report (METAR) for KBQM, issued at 1210, reported winds variable at five knots, gusting to 14 knots, visibility ten miles, sky condition scattered clouds at 2,000 feet, temperature 22 degrees Celsius (C), dew point minus 16 degrees C, and an altimeter of 29.90 inches of Mercury (Hg).
WRECKAGE AND IMPACT INFORMATION
The accident site was located just north of the approach end of runway 19 in level terrain. Tall deciduous trees were located in the immediate vicinity of the wreckage. The accident site was at an elevation of 1,280 feet msl.
The wreckage consisted of the fuselage, empennage, both wings, and the engine and propeller assembly. The debris field was contained to an area measuring twenty feet by twenty feet square. The airplane was recovered from the scene and relocated to a facility in Lancaster, Texas, for further examination.
MEDICAL AND PATHOLOGICAL INFORMATION
The Travis County Office of the Medical Examiner, Austin, Texas, performed the autopsy on the pilot on November 15, 2009, as authorized by the Justice of the Peace, Precinct 1, Burnet County, Texas. The autopsy report concluded that the pilot “died as a result of blunt force injuries.”
The FAA’s Civil Aerospace Medical Institute, Oklahoma City, Oklahoma, performed toxicological tests on specimens that were collected during the autopsy (CAMI Reference #200900288001). Results were negative for all tests conducted.
TESTS AND RESEARCH
An investigator with the National Transportation Safety Board (Safety Board) examined the wreckage on December 22, 2009. The airplane had been cut in two, just aft of the crew seats, for transportation purposes. Both wings were crushed and bent and exhibited aft accordion crushing. The empennage, to include the horizontal and vertical stabilizer, elevator, and rudder, were unremarkable. Control continuity was verified to the left and right aileron, elevator, and rudder controls.
The engine remained attached to the forward portion of the fuselage. Engine continuity was established by rotating the propeller through by hand. Rocker arm movement was visually observed. Compression was tacitly observed at each upper spark plug orifice.
The airplane was equipped with two fuel tanks; forward, and aft. The aft fuel tank contained fuel; however, the forward fuel tank was empty. The fuel line from the forward fuel tank to the engine had separated as a result of the accident. The forward tank fuel selector valve was selected to the main position and the aft fuel selector valve was selected to the off position.
Further examination of the forward fuel tank noted a white substance lining the bottom and sides of the tank and appeared to be broken into multiple pieces. The finger strainer was removed from the bottom of the fuel tank and found to be blocked, approximately 80 percent, with a white substance similar to the substance on the inside of the fuel tank. The fuel tank was opened for further examination, revealing multiple pieces of white debris in sizes ranging from one inch to twelve inches. The substance left a powder film when handled. A portion of this white substance and the forward fuel tank were retained for further examination.
The white substance, the fuel tank, and the finger screen were sent to the Safety Board Materials Laboratory in Washington, D.C. An inside view of the fuel tank from the access hole cut into the side of the tank revealed a white powder on the walls of the fuel tank and a deposit layer on the inside bottom of the tank consistent with a cured-in-place polymer liquid. The deposit layer was completely disbonded from the bottom of the tank. The deposit layer exhibited three distinct morphologies: a thick green region; a gray region; and a thin silver region. Samples from the fuel tank contents and the fuel tank were sent to an independent lab for further examination.
Fourier-Transform Infrared (FTIR) spectroscopic analysis of the thick green layer, the gray layer, and the thin silver layer matched each other, indicating that the three samples were all the same material. The presence of polyurethane was found in the FTIR spectra of the deposit samples. The FTIR spectrum for the white residue was found to be a best match for polyether urethane or polyurethane. The FTIR spectrum confirmed that the tank from the accident aircraft was made of polyethylene.
An examination and measurement of the fuel finger screen revealed a mesh measurement consistent with 32 mesh screen.
Prior to the recovery of the airplane an airworthiness inspector, with the San Antonio Federal Aviation Administration (FAA) Flight Standards District Office, removed the carburetor and sent it to the engine manufacturer for further examination. This action was taken without prior knowledge of the Safety Board, and there was no federal oversight present when the examination was conducted. The examination revealed corrosion and the build-up of an unknown substance on the carburetor jet needle. This build-up prevented the correct functioning of the fuel and air mixture in the carburetor. No other anomalies were noted with the carburetor.
Sonex Aircraft LLC
According to Sonex Aircraft, LLC, the airplane kit included one 16 gallon plastic fuel tank assembled from cross-linked polyethylene. The manufacturer advised that builders should utilize a 16 mesh fuel finger strainer in the assembly of their fuel tank. In 2008 Sonex Aircraft, LLC introduced the Oops fitting which was designed to address leaking and loose fitting issues in the fuel tank.
In June of 2008 Sonex issued revision B of their Fuel Tank Installation and Warranty builder’s guide. In this revision they noted that the fuel tank is made from “an incredibly strong material but one which also resists most chemicals, including adhesives.” They stated further in this revision that if a leak occurred, the only acceptable repair was a replacement of the fuel tank.
In March of 2010 revision C was issued with a manufacturer “Warning!” against the utilization of a sloshing compound to seal the fuel tank. They wrote that “sloshing compounds do not adhere to the plastic tank and will plug and contaminate your fuel system.” Both revision B and revision C were published on the Sonex website and available to Sonex builders. In addition, this document was sent with each new fuel tank. Prior to these revisions, the recommendation to builders with leaks was to replace the fuel tank.
Fuel Tank Contaminants
According to the mechanic who performed the last condition inspection on the accident airplane, there were no anomalies with the airplane, engine, or fuel tank and he was not aware of any fuel leaks with the airplane. He remarked that the fuel bowl and main fuel line were free of contaminations at the time of the inspection. He also commented that he did not inspect the fuel tank finger screen as this was not routinely removed during annual examinations.
According to the builder of the accident airplane, the forward fuel tank started leaking approximately 10 to 20 hours into the operation of the airplane. He did not want to remove the entire fuel tank so he removed the leaking fitting and added Por-15, a fuel tank sealant, to stop the leak. He reported that the airplane had flown for an additional 100 hours without issues before he sold it to the accident pilot.
A review of the maintenance records did not reveal a log book entry for this procedure. Based upon the time frame provided by the builder, this would have placed the procedure prior to August 21, 2005, where the first airframe time of 51 hours was reported.
Por-15 manufactures a fuel tank sealant designed to seal fuel tank leaks. The instructions from the manufacturer (POR-15/FTS) describe procedures for cleaning the fuel tank, patching the outside of the tank, and answers questions on the basic applications and utilizations of the fuel tank sealer. Their information did not discuss and did not specifically prohibit or advise against the use the sealant in a plastic fuel tank application. In conversation with the manufacturer, they confirmed that the sealant was not designed to be utilized in a plastic fuel tank application.