Mariposa, CA, USA
N6054Q
WILLIAMS MYRON G BOWERS FLY BABY 1A
The plans-built single-seat airplane had been constructed about 8 years before the accident by another individual, who had flown it about 30 hours before it was purchased by the current owner/pilot. In the year since the purchase, due to the low build-quality of the airplane, the pilot had made several modifications and repairs to the airplane. The accident flight was the pilot's fifth flight in the airplane. Review of the pilot's flight logbook indicated that his most recent flight review occurred about 7 years before the accident and that he had flown only 15 hours in the 2 years before the accident. A witness reported that shortly after takeoff, when the airplane was about 3 miles from the airport, the engine began making a sound as if power was intermittently being interrupted. The nose of the airplane began to pitch up aggressively as it flew out of view. The wreckage location, wreckage distribution, and impact signatures indicated that the airplane struck the ground in a steep nose-low attitude, consistent with an aerodynamic stall event. Postaccident examination of the carburetor revealed multiple maintenance-related discrepancies, any one of which could have resulted in the loss of engine power. Additionally, before the accident, the pilot reported to a friend that the airspeed indicator was not reliable and that the airplane exhibited roll control anomalies. Both of these conditions would have hindered the pilot's ability to safely operate the airplane.
HISTORY OF FLIGHTOn April 11, 2014, at 1007 Pacific daylight time, an experimental amateur-built Bowers (Williams Myron G) Fly Baby 1A, N6054Q, collided with wooded terrain near Mariposa, California. The airplane was registered to, and operated by, the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. The commercial pilot sustained fatal injuries; the airplane sustained substantial damage to the forward fuselage and both wings during the accident sequence. The local flight departed Mariposa-Yosemite Airport, Mariposa, about 0950. Visual meteorological conditions prevailed, and no flight plan had been filed. A witness located about 3 miles northwest of Mariposa Airport, was outside and observed an airplane approaching from the southeast flying at an altitude of about 1,000 feet above ground level (agl). The airplane began a left turn as it approached, and appeared to be descending. He described the engine as making a "missing" sound, as if power was intermittently being interrupted. The airplane then began a right turn, arcing around his location, and by the time it had passed behind him, it had descended to an altitude of about 300 feet agl. It then gradually rolled out of the turn and proceeded to fly towards the hills to the northeast. By then, the engine sound appeared muffled, and the airplane appeared to have slowed down considerably. The nose began to pitch up to about 30 degrees, almost parallel with the slope of the hill, as the airplane disappeared out of the witness's view behind trees. He did not hear any other sounds, but assumed the airplane had crashed. He then asked a family member to call 911; dispatch records from the Mariposa County Sheriff department revealed that the call was made at 1008. PERSONNEL INFORMATIONThe 80-year-old-pilot held a commercial pilot certificate with ratings for airplane single-engine land, and instrument airplane issued in 1972. His most recent Federal Aviation Administration (FAA) third-class medical certificate was issued in October 2007, with limitations that he possess glasses that correct for near vision. At the time of his last medical application, the pilot reported a total flight time of 1,800 hours. An entry in the pilot's flight logbook dated June 22, 2013, indicated that he had received 0.6 hours of flight training with an instructor in a Cessna 152, practicing "maneuvers, stalls, slow flight"; however, the most recent documented flight review was completed in November 2007. According to the logbook, his total flight experience in the two year period preceding the accident was 15.1 hours. His total experience in the accident airplane was 3.1 hours, all of which occurred during 4 flights in the month leading up to the accident. AIRCRAFT INFORMATIONThe plans-built, single-seat, low-wing airplane's primary structure was comprised of wood covered in fabric, with the wings and landing gear braced by steel wires. The airplane was powered by a four-cylinder Continental A65-8 engine, and equipped with a wooden two-blade propeller. The airplane was issued its special airworthiness certificate on October 20, 2006, and that same day, was involved in an accident after losing power on its maiden flight. The pilot/builder self-reported that the loss of power was most likely caused by his failure to use carburetor heat, and the NTSB determined the probable cause of the accident to be, "a loss of engine power due to the pilot's failure to use carburetor heat during conditions that were conducive to carburetor icing." The airplane was sold to the accident pilot in December 2012, with maintenance logbooks indicating that it had accrued a total of 29 flight hours. The logbooks indicated that over the next 3 months the pilot performed a series of repairs to the brakes, control surfaces, and flying cables, as well as replacing the propeller and right magneto cap. The pilot reported to a friend that the build quality of the airplane was "crude," and that he intended to progressively restore the airplane to an airworthy condition. The airplane subsequently underwent a series of taxi tests in March 2013, but was not flown for the remainder of the year. On March 3, 2014, an annual inspection was completed by an FAA certified airframe and powerplant mechanic, who held an inspection authorization rating. The mechanic stated that prior to his examination the engine was backfiring, and the pilot had not been able to successfully resolve the problem. The mechanic subsequently discovered that the magneto leads to two cylinders had been transposed. The first flight followed shortly thereafter, and according to the pilot's friend, was an accidental flight when the airplane broke ground during a high speed taxi test. About 2 weeks prior to the accident, the pilot performed an intentional flight test. During that flight he experienced flight control difficulties in roll. He also stated that the airplane's airspeed indicator was not performing consistently, and that he planned to move the Pitot tube further outboard on the wing, away from the propeller slipstream. METEOROLOGICAL INFORMATIONThe closest weather reporting station at an elevation similar to the accident site was located at Columbia Airport, Columbia, California; this was situated about 36 miles north-northwest of the accident location. The 1015 Columbia automated report indicated calm wind, sky clear, temperature of 23 degrees C, dew point 06 degrees F, and an altimeter setting at 29.93 inches of mercury. AIRPORT INFORMATIONThe plans-built, single-seat, low-wing airplane's primary structure was comprised of wood covered in fabric, with the wings and landing gear braced by steel wires. The airplane was powered by a four-cylinder Continental A65-8 engine, and equipped with a wooden two-blade propeller. The airplane was issued its special airworthiness certificate on October 20, 2006, and that same day, was involved in an accident after losing power on its maiden flight. The pilot/builder self-reported that the loss of power was most likely caused by his failure to use carburetor heat, and the NTSB determined the probable cause of the accident to be, "a loss of engine power due to the pilot's failure to use carburetor heat during conditions that were conducive to carburetor icing." The airplane was sold to the accident pilot in December 2012, with maintenance logbooks indicating that it had accrued a total of 29 flight hours. The logbooks indicated that over the next 3 months the pilot performed a series of repairs to the brakes, control surfaces, and flying cables, as well as replacing the propeller and right magneto cap. The pilot reported to a friend that the build quality of the airplane was "crude," and that he intended to progressively restore the airplane to an airworthy condition. The airplane subsequently underwent a series of taxi tests in March 2013, but was not flown for the remainder of the year. On March 3, 2014, an annual inspection was completed by an FAA certified airframe and powerplant mechanic, who held an inspection authorization rating. The mechanic stated that prior to his examination the engine was backfiring, and the pilot had not been able to successfully resolve the problem. The mechanic subsequently discovered that the magneto leads to two cylinders had been transposed. The first flight followed shortly thereafter, and according to the pilot's friend, was an accidental flight when the airplane broke ground during a high speed taxi test. About 2 weeks prior to the accident, the pilot performed an intentional flight test. During that flight he experienced flight control difficulties in roll. He also stated that the airplane's airspeed indicator was not performing consistently, and that he planned to move the Pitot tube further outboard on the wing, away from the propeller slipstream. WRECKAGE AND IMPACT INFORMATIONThe airplane came to rest at the base of an oak tree, within densely wooded terrain at an elevation of 2,250 feet mean sea level (msl), about 3 miles northwest of Mariposa Airport. The terrain surrounding the accident site was comprised of grass and poison oak, interspersed with rocky outcroppings and various oak trees ranging in height from saplings to 20 feet tall. The airplane came to rest on a magnetic heading of about 60 degrees, facing uphill on a 20-degree slope. A freshly cut swath through the tree branches was located directly above the airplane; the swath was nearly vertical. Although the airplane was surrounded by trees, no other damage to limbs or branches was noted. The wings came to rest inverted, with the forward fuselage and engine located underneath the wing root. The tailcone and empennage structure had separated aft of the seat, and was resting undamaged on its right side. Both wings sustained aft crush damage to their leading edges. The entire cabin structure forward of the tailcone was fragmented, and the firewall was compressed against the rear of the engine. All cockpit flight controls exhibited varying degrees of bending damage, but remained functionally intact. The fuel tank sustained multiple breaches, and was detached but still located within the center section of the wreckage. The airframe and engine did not display any indications of bird strike or fire. The engine remained attached to its mount, which remained attached to the firewall. Both magnetos (Eisemann, Model AM-4) remained firmly attached to the engine, however, their plug caps had both fragmented, crushing and exposing the timing gears, points, and coils, as well as detaching all ignition wires and both P-leads. The carburetor had broken away from the inlet manifold, and the inlet air filter assembly exhibited crush damage. The throttle cable was attached and continuous from the cockpit to the butterfly valve; the cable was in the full-forward position at the cockpit control. The carburetor heat control cable was continuous from the cockpit control to the heat box. The control was in the aft (carburetor heat on) position. The fuel primer was in the forward and locked position. The top spark plugs were removed and examined. They were of the three-prong type, with the electrodes covered in grey deposits and exhibiting minimal wear. The inner surfaces of the exhaust pipes exhibited light grey deposits, and were free of oil residue. The crankshaft turned smoothly when rotated by hand utilizing the propeller hub, and compression was noted on all cylinders. Mechanical continuity was established throughout the rotating group, valve train, and accessory section. Visual inspection of the combustion chambers was accomplished through the spark plug bores utilizing a borescope; there was no evidence of catastrophic internal damage, and all combustion surfaces exhibited light grey deposits. The hub of the wooden propeller remained attached to the crankshaft, and was embedded in the soil below the engine. The blades were fragmented, and multiple fragments were located resting in trees branches and on the ground east of the wreckage. The furthest propeller fragments were located about 40 feet from the main wreckage. The on-scene examination did not reveal any pre-impact airframe or engine anomalies that would have precluded normal operation, and all airframe components were accounted for within the immediate vicinity of the accident. A detailed report is contained within the public docket. ADDITIONAL INFORMATIONFueling records from Mariposa Airport indicated that the pilot purchased 5.12 gallons of 100 octane low-lead aviation gasoline about 1 hour prior to the accident. Daily records provided by Shell Aviation revealed that the fuel in the airport's tanks was clean and clear during the week leading up to the accident. Three other aircraft were serviced with fuel from the same tank on that day, and none reported problems. The airplane met the FAA criteria for the light sport aircraft category, and the pilot's stated medical status along with his commercial pilot rating allowed him to operate with sport pilot privileges. As such, he was not required to hold a current FAA medical certificate. The carburetor icing probability chart from FAA Special Airworthiness Information Bulletin CE-09-35, Carburetor Icing Prevention, dated June 30, 2009, shows a probability of "icing at glide power" at the temperature and dew point reported at the time of the accident. MEDICAL AND PATHOLOGICAL INFORMATIONAn autopsy was conducted by the Stanislaus County Sheriff's Department, Coroners Division, on behalf of the Mariposa County Coroner's Office. The cause of death was reported as the effect of blunt injuries, with no other contributing conditions. Toxicological tests on specimens recovered from the pilot were performed by the FAA Civil Aerospace Medical Institute (CAMI). Analysis revealed negative findings for carbon monoxide and ethanol with the following positive drug findings: >> Warfarin detected in Urine >> Warfarin detected in Blood (Cavity) Refer to the toxicology report included in the public docket for specific test parameters and results. According to CAMI, Warfarin is an anticoagulant medication, with no specific warnings pertinent to flight. TESTS AND RESEARCHCarburetor The Stromberg NA-S3B carburetor was examined at the facilities of Uni-Tech Air Management Systems, Kankakee, Illinois in the presence of the NTSB investigator-in-charge. The carburetor serial, "Continental", and model numbers correlated to the gravity fuel-feed application for use with a Continental A-50 or A-65 engine. The carburetor was of the "low-altitude" fixed mixture control type, and was therefore not configured with a cockpit adjustable mixture control arm. The carburetor sustained minimal damage and was externally examined. No obvious fuel leaks were observed, and according to the Uni-Tech representative, the fuel inlet hose was of the automotive type. No safety wire was present on the venturi retainer or the throttle valve lock adjustment screws. The idle screw mixture appeared to be set at 3/4 of a turn back from fully closed, rather than the typical 3 turns. The Uni-Tech representative stated that it was not common to see an idle mixture screw set so low. The throttle control arm moved smoothly when manipulated by hand. The arm was moved to the fully closed position, and the throttle valve completely obscured the venturi orifice. No gap was observed between the valve and the throat in this position, indicative of an incorrectly adjusted valve stop screw. According to the Uni-Tech representative, a valve without a gap at the venturi intersection results in an almost completely closed air inlet, and would inhibit or limit the engine's ability to operate at idle speed. The control lever was then moved to the full-open position, and the valve appeared to open beyond its center position by about 5 degrees. The fuel bowl was separated from the upper casing, and internal components were examined. An undamaged Delrin float needle had been installed, with the appropriate rounded valve seat; however, no accompanying brass float balance weight had been installed as required by Bendix (Stromberg) Service Bulletin Number 84. Examination of the engine maintenance logbooks revealed an unattributed entry dated March 10, 2006 (before the first accident), stating, "Installed delron needle in carburetor". The entry did not indicate the installation of the accompanying float weight. The main metering jet body appeared to be touching the float base, preventing full travel of the float. The float drop was then measured at the valve needle and exhibited 0.019 inches of travel as opposed to the minimum specified in Stromberg documentation of 0.048 inches. The bowl assembly was mounted and leveled on a flow gauge test assembly, and fuel was applied to the inlet at a pressure of 1 psi. The float moved upwards, and fuel immediately overflowed out of the bowl consistent with binding of either the float or float assembly. The operation was tried again, and this time the fuel flow stopped once it had reached within 1/16th of an inch from the bowl seam. According to Stromberg specifications, the fluid level (float level) should be 13/32nds of an inch from the seam. The float and float pin assembly was remov
The partial loss of engine power due to an improperly maintained carburetor and the pilot's subsequent failure to maintain aircraft control.
Source: NTSB Aviation Accident Database
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