NTSB Factual Report

HISTORY OF FLIGHT

On October 22, 2011, about 1251 eastern daylight time, a Berger Waiex, N75654, was substantially damaged following an inflight breakup and collision with terrain near Washington, Georgia. The certificated sport pilot was killed. The experimental, amateur-built (E-AB) airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations (CFR) Part 91 as a personal flight. Visual meteorological conditions prevailed and no flight plan was filed. The local flight originated at Washington-Wilkes County Airport (IIY), Washington, Georgia about 1239.

A review of radar and Garmin 510 Global Positioning System (GPS) data revealed that the airplane departed IIY about 1239, and the pilot began a gradual, climbing turn to the north. About 2 nautical miles (nm) northeast of IIY, the airplane was observed climbing in left-hand circular patterns until a peak altitude of 4,700 feet above mean sea level (msl) was reached. The airplane then continued on a westerly heading until the GPS stopped recording data. The last two recorded radar returns with altitude data were at 4,600 and 4,300 feet. Prior to the last radar return, the airplane was in a slight descent and accelerated to about 100 to 110 knots ground speed. The GPS did not capture the parameters when aircraft control was lost. The wreckage site was located about 0.11 nm north-northeast of the last radar return with altitude information.

Local deer hunters were outside, about one-quarter mile northwest of the accident site, at the time of the accident. They heard a loud noise and looked up to see what they thought was the airplane's tail, falling out of the sky. They also heard the engine stop running prior to the crash. They immediately proceeded toward the accident site and called 911 for assistance.

Another witness, who was outside his residence at the time of the accident, reported that he heard the airplane's engine stop running. He could see the airplane through the trees on his property, and the airplane was tumbling downwards, "…end over end."

PERSONNEL INFORMATION

The pilot held a sport pilot certificate, issued November 3, 2009. He reported a total flight experience of 29.9 hours on his sport pilot certificate application, including 5.8 hours as pilot in command. The pilot's personal logbook was not located; however, according to the maintenance logbooks, about 53 hours of flight time were recorded on the aircraft since the pilot purchased it on April 13, 2011.

AIRCRAFT INFORMATION

The airplane was built in 2007 and the pilot purchased it from the builder. According to representatives from Sonex Aircraft, LLC, the kit manufacturer, a Waiex (pronounced "Y-X") is a Sonex in a "Y-tail" configuration. For the purposes of this report, the terms "V-Tail" and "Y-Tail" are used interchangeably. According to the maintenance logbooks, the airplane had accumulated about 300 hours total time since its manufacture.

The airplane was a single engine, low wing, fixed tail wheel airplane, serial number WX-0087. It was powered by an Aerovee 2.1 engine rated at 80 horsepower.

According to the aircraft maintenance records, the last condition inspection on the airframe and engine was performed on February 12, 2011, at a total aircraft time of 144.2 hours. The last recorded airframe maintenance occurred on October 21, 2011, at 300.6 hours total aircraft time, when the brakes were changed. The last recorded engine maintenance occurred on September 28, 2011, when the oil, oil filter, and spark plugs were changed.

METEOROLOGICAL INFORMATION

The 1351 surface weather observation for Athens, Georgia (AHN), located about 28 nautical miles (nm) west-northwest of the accident site, reported wind calm, visibility 10 miles or better, sky clear, temperature 18 degrees C, dew point 4 degrees C, and altimeter setting 30.12 inches of mercury.

WRECKAGE AND IMPACT INFORMATION

The aircraft wreckage, except for its Y-tail assembly, was found in a wooded ravine, about 2.3 nautical miles north of IIY. The coordinates of the main wreckage were 33 48.97N and 082 49.23W. The Y-tail was found separated, near a dirt road, about 550 feet southwest of the main wreckage. The coordinates of the Y-Tail were 33 48.91N and 082 49.31W. The fuselage was found inverted, resting against a pine tree. The engine remained attached to the airframe and the propeller remained attached to the engine. One blade of the propeller was broken off at the root; the other blade remained attached to the hub. The blades did not display evidence of rotational damage.

The aircraft fuel tank contained less than one ounce of fuel and was not breached. There was no odor of fuel observed at the main wreckage site. There was no evidence of spilled fuel under the wreckage.

Flight control continuity was established from the ailerons to the cockpit controls. The flaps were observed in the "retracted" position. Control continuity was established from the cockpit controls to the fractured surface attachment points on the Y-tail.

General examination of the aircraft structure revealed several areas of "less-than-optimal" construction techniques. These included a lack of deburring drilled holes, notching from metal cuts that were not smoothed out, excessive chamfers, mis-drilled holes, and the use of oversized washers to cover mis-drilled holes. For more information on this subject, refer to the Structures Study, located in the public docket for this accident.

The engine throttle was found about 0.25 inches aft of the "full forward" position. The fuel mixture knob was in the "full forward" position. The engine was free to rotate when the crankshaft was turned by hand. Compression and suction was observed on all cylinders when the crankshaft was rotated. The carburetor was removed for examination; it showed no evidence of obstructions or contamination. The spark plug electrodes were light gray in color and did not exhibit abnormal wear.

MEDICAL AND PATHOLOGICAL INFORMATION

A postmortem examination of the pilot was performed by the Georgia Bureau of Investigation, Division of Forensic Sciences, on October 25, 2011. The autopsy report noted the cause of death as "Multiple blunt force injuries" and the manner of death was "Accident." The report also noted that the pilot had "…an enlarged heart with coronary atherosclerotic disease." There was no evidence of acute or remote infarcts.

Forensic toxicology testing was performed on specimens of the pilot by the Federal Aviation Administration (FAA) Bioaeronautical Sciences Research Laboratory (CAMI), Oklahoma City, Oklahoma. The CAMI toxicology report indicated negative for carbon monoxide, cyanide, and ethanol. Metoprolol and rosuvastatin were detected in the urine and blood, and ticlopidine was detected in the urine, but not in the blood.

Metoprolol (Toprol XL ®) is a prescription selective beta1-adrenoreceptor blocking agent used to treat high blood pressure, angina and control heart rate in some arrhythmias. Rosuvastatin (Crestor®) is a prescription lipid lowering agent used to treat elevated blood lipids and elevated cholesterol. Ticlopidine (Ticlid®) is a prescription platelet aggregation inhibitor used as adjunctive therapy with aspirin to reduce the incidence of subacute stent thrombosis in patients undergoing successful coronary stent implantation; it is also used to reduce the risk of stroke in people who have had a stroke or have had warning signs of a stroke and who cannot be treated with aspirin.

The pilot did not possess a current FAA airman medical certificate. He possessed a valid and current Georgia driver’s license. He was issued a Special Issuance (SI) third class airman medical certificate on December 1, 2008, with an expiration date of December 31, 2009. The pilot did not apply for a renewal of the SI. The SI noted a history of angina pectoris, coronary artery disease requiring percutaneous transluminal coronary angioplasty with stent implantation, hypertension which required medication for control, and post-traumatic stress disorder (PTSD).

TESTS AND RESEARCH

Components of the Y-tail were submitted to the NTSB Materials Laboratory for examination.

Forward Tail Connection

The forward tail connection (lower attach angle, part number XNS-T09-04) was a single 9.5 inches long, 1/8 inch thick, L-shaped profile, connected to the fuselage with two bolts placed near the ends of the horizontal flange of the profile and to the tail assembly with six bolts evenly distributed along the vertical flange of the profile.

The profile was transversely fractured, separating the horizontal and vertical flanges. Fracture features such as shear lips and rough matte grey surfaces indicated tensile and shear overstress fracturing. There were no indications of fatigue or other progressive crack growth. The profile fracture exhibited a 2.5 to 3 inches long tensile overstress in the vertical flange. The tensile region was at the right edge of the vertical flange, near the profile's fillet. The rest of the profile was fractured by shearing overstress in the horizontal flange.

The horizontal flange of the profile showed out-of-plane deformation, along with clear longitudinal elongations of the bolt holes. The vertical portion of the profile did not show any out-of-plane or within-plane deformation, but the two rightmost bolt holes exhibited elongation in the vertical direction.

Aft Tail Connection

The aft tail connection consisted of two Y-shaped plates, one 3/16 inch and the other 1/8 inch thick, bolted together at numerous locations. Both the legs and the arms of the plates were (excluding the tongues of the thinner plate) 2.25 inch wide. The vertical legs of the plates connected to the fuselage, and the arms spread to the tail assembly.

Both plates showed similar overstress fracture characteristics. The fracture surfaces indicated a tensile overstress in the vertical direction, along the entire width of both plates. The fracture surfaces were more erratic (shifting planes) on the left side, as compared to the right side. There were no indications of fatigue crack growth.

Both plates exhibited similar plastic deformations at the left side of the fracture. These deformations locally distorted the left sides of the plates toward the left and aft, with respect to the aircraft.

The bolt holes in the right sides of the Y plates and in the short L profile were elongated in the vertical direction. The portions connected to the fuselage also exhibited yielding around the right side holes at or near the fractures.

Not all surfaces were clean and smooth. Not all holes were clean and deburred. However, holes which were included in the fracture zone (only applicable to the rear connection), were deburred, some excessively.

For additional information and photographs, refer to the Materials Laboratory Factual Report, located in the public docket for this accident.

Breakup Sequence

The breakup appeared to have initiated in the forward Y-tail attachment structure (lower attach angle). The lower attach angle separated in tension along the right side and further separated with the fracture running from the right to the left. As the lower attach angle was breaking, the structure that formed the aft connection Y-fitting also fractured and separated. For additional information and graphics regarding the breakup sequence, refer to the Structures Study, located in the public docket for this accident.

ADDITIONAL INFORMATION

The Waiex E-AB airplane was designed by Sonex Aircraft, LLC, who supplied kits and drawings to individuals for their personal construction and recreational flying. Sonex Aircraft, LLC stated that the company used CFR Part 23, Appendix A, Simplified Design Load Criteria for both the Waiex and Xenos aircraft Y-tail designs. Sonex used a pre-1996 version of the CFR Part 23 Appendix A regulations. According to company personnel, most of the design work on the Waiex was accomplished in 2002 and 2003. The first Waiex plan sale occurred in June, 2004.

There are no required design standards or criteria for E-AB airplanes. The current FAR Part 23 standards are used for certificated small airplane designs.

The pre-1996 versions of 14 CFR Part 23, Appendix A, stated that the design load criteria in the appendix were an approved equivalent for the certification of conventional, single-engine airplanes of 6,000 pounds or less maximum weight. The 14 CFR Part 23 criteria were based on Civil Aeronautics Regulations (CAR) Part 3.

CAR Part 3 specifically stated that the design charts in Part 3.211 (Control Surface Loads) did not apply to V-tail assemblies. In general, the surface loads on a V-tail configuration may be greater than the design loads expected on the surfaces of a conventional tail airplane. For conventional tail plane surfaces, changes in angle of attack primarily affect the loads on the horizontal surfaces and changes in side slip angle primarily affect the loads on the vertical surfaces. However, for V-tail airplanes, changes in angle of attack and sideslip angle can simultaneously increase the loads on one of the surfaces. In addition, stick and rudder pedal input may also add to the loads on one of the surfaces.

However, there was no readily identifiable definition of "conventional airplane." The 1996 revision of Appendix A removed the reference to "conventional airplane" and added an expanded section defining the applicability of Appendix A. The expanded definition explicitly excluded using Appendix A criteria when designing the V-tail configurations of certified airplanes.

Thus, the V-tail configuration was not recognized as conventional in CAR Part 3, and when CAR Part 3 was later codified at 14 CFR Part 23, this did not change. The 1996 change to 14 CFR Part 23 clarified the V-tail design exclusion. After the accident, the Sonex Aircraft Engineering Team evaluated the damaged components and subsequently issued a service bulletin WIX-SB-001 11.15.11 that required that an aluminum block be added at the point of the tension separation. The information can be found at http://www.sonexaircraft.com/support/servicebulletins.html.

NTSB Probable Cause

The in-flight failure of the aircraft’s Y-tail attachment structure during maneuvering flight due to overload. Contributing to the accident was, the kit manufacturer’s use of 14 CFR Part 23, Appendix A design guidelines intended for a conventional tail airplane without a V- (or Y-) tail.