ERA15FA331

Separation of the vertical and horizontal stabilizers from the fuselage due to a fracture that initiated at the bond between the left horizontal stabilizer and the flange that attached the horizontal stabilizer to the fuselage skin. The failure was likely caused by construction techniques that produced poor bond strength in a critical area and the high loads on the horizontal stabilizer from a single or multiple aerobatic maneuver(s).

The commercial pilot was practicing his airshow routine in the experimental amateur-built airplane for a performance scheduled the following day. He had completed several maneuvers and was about 5 minutes into the routine when the tail section of the airplane separated from the fuselage during a 45° upline maneuver as the airplane began a left aileron roll. The pilot had performed several aileron rolls, both left and right, at varying pitch attitudes earlier in the routine. Examination of the wreckage revealed that the fractures that resulted in separation of the tail section likely initiated at the bond between the lower surface of the horizontal stabilizer and the flange attaching the horizontal stabilizer to the left side of the fuselage. The bond failed in tension, consistent with the left side of the horizontal stabilizer moving upward relative to the fuselage (or the fuselage moving downward relative to the horizontal stabilizer). Microscopic examination of the bond surfaces revealed two relatively small regions of poor bond integrity, as evidenced by a lack of fiber pullout or resin transfer between the mating surfaces of the flange and the underside of the horizontal stabilizer. One of these regions was in the area where the bond fracture likely originated. Poor bond quality can result from poor or improper surface preparation before the bond is made, such as improper sanding and incomplete cleaning of the surfaces to be bonded. These two regions contained score marks consistent with having been sanded, as was specified in the build directions. It is possible that these two regions were not thoroughly cleaned or became contaminated after cleaning before the bond was made. Contamination from dust, oil, or other substances could have prevented the resin from adhering to the surface in those regions. Fourteen years before the accident, in France, another airplane of the same make and model had an in-flight separation of the tail during wings-level flight after performing aerobatic maneuvers. The investigation discovered a similar lack of fiber pull-out or resin transfer in the bond fracture of the same joint. In that case, there were several areas with these features that covered a much larger portion of the bond surface. Both airplanes exhibited evidence of poor bonding between the horizontal stabilizer and the flange attaching it to the fuselage, a condition that most likely occurred during their manufacture, and both had accrued several hundred flight hours before the bonds failed. The accident airplane was manufactured about 17 years prior to the accident. Although it had been flown in multiple aerobatic competitions and airshows, no evidence of progressive crack growth was observed emanating from the origin area on the fracture surface. This suggests the possibility that the bonds may have fractured after being exposed to higher loads at the time of ultimate failure, rather than the load factors to which they had previously been exposed. However, in both accidents, the tail separation occurred during a maneuver that was relatively benign compared to other maneuvers flown earlier in their flights. The tail section failure on the accident airplane occurred during an aileron roll while on an upline, which would have applied loads to the horizontal stabilizer that were asymmetric (upward on the left stabilizer, consistent with the direction of the initiating "L" flange bond failure, and downward on the right stabilizer), but likely not the highest loads achieved during the accident flight. The airplane vertical load factor during the preceding pull-up maneuver was relatively high, estimated to be between +6 and +9 g. However, the loads on the horizontal stabilizer at that time should have been downward on both sides, which is inconsistent with the tensile fracture of the left "L" flange bond. The recording g-meter found at the accident site indicated the peak load factors reached during the flight were +8 and -4.75 g. Assuming the peak needles were set to 0 before the flight and did not move appreciably during impact, it is likely that the airplane did not exceed the airplane design limits of ± 10 g for vertical load factor during the accident flight. However, the relationship between peak vertical load factor and the strength of the compromised bonds of the "L" flanges is unknown. The airplane had also performed several other maneuvers during the flight, including snap rolls and aileron rolls in both directions. It is possible that the bond had failed or partially failed during one or more previous maneuvers during the accident or during previous flights. While no evidence of progressive crack growth was found in the bond fracture features, failure of multiple elements of the structure were required to produce the observed separation. It is possible that the bond fracture developed over the course of several or many maneuvers without leaving obvious evidence of progressive damage on the fracture surface. Although the "L" flanges in the accident airplane were constructed using three plies of fiber-reinforced cloth, as opposed to the specified four, the lack of the fourth layer likely did not contribute to this accident, as the originating failure was in the bond between the flange and the horizontal stabilizer surface. In addition, the investigations of both accidents revealed that the "L" flanges and their bonds to their mating surfaces are critical to the strength of the skin joints between the fuselage and the horizontal stabilizer and the vertical stabilizer. The investigation revealed that no snap roll entry speed limitation was designated for this airplane, nor is it for many other aerobatic airplanes, due to a lack of criteria. Snap rolls place considerably high and asymmetrical loads on the horizontal stabilizer. As a result of this investigation, the airplane designer developed an inspection procedure for the empennage, a reminder about common airspeed limitations that should be established, and a suggestion for establishing a snap roll entry speed limitation. Although the pilot's toxicology results tested positive for Zolpidem, the values were below the normal therapeutic range and there was no evidence that impairment played any role in causing or contributing to the tail separation.

The Office of the Chief Medical Examiner, Orange County, New York, conducted an autopsy on the pilot. The cause of death was determined to be "blunt impacts of head, torso, and extremities." The FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, conducted toxicological testing of specimens from the pilot. The testing was negative for ethanol and drugs of abuse. Zolpidem, a prescription medication used in the treatment of insomnia, was detected in the liver and cavity blood. This medication may impair mental and/or physical ability required for the performance of potentially hazardous tasks (e.g., driving, operating heavy machinery). Due to adverse side-effects, the FAA recommends waiting at least 24 hours after use before flying. The 1345 recorded weather observation at SWF included scattered clouds at 4,000 ft above ground level, wind from 290° at 8 knots, visibility 20 statute miles, temperature 22°C, dew point 13°C, and an altimeter setting of 30.19 inches of mercury. The pilot, age 53, held a Federal Aviation Administration (FAA) commercial pilot certificate with airplane single engine land and instrument airplane ratings. He was issued a Statement of Acrobatic Competency on March 17, 2014 with a maneuver limitation of solo aerobatics, and an unrestricted altitude limitation. He held an FAA second class medical certificate issued on May 19, 2015, with a restriction for corrective lenses. A review of the pilot's logbook revealed that he had 3,215 total hours of flight experience as of August 23, 2015, with about 1,000 hours in the accident airplane make and model. The fuselage came to rest on its left side and was heavily fragmented. The right wing separated from the fuselage and came to rest about 30 ft southwest of the main wreckage. The left wing was also separated and found adjacent to the main wreckage. Both wings showed heavy fragmentation of the leading edge, and large sections had fractured and separated from each wing. Flight control continuity was confirmed from the control stick to both ailerons and the elevator through overload fractures in the rod ends of the push-pull tubes. Continuity was established from the rudder pedals, which had separated from the fuselage structure, to the rudder through overload fractures in the left rudder cable and in the right rudder control horn. The engine came to rest partially embedded in soil with both of the wooden propeller blades separated near the hub. A second debris field was located about 1,800 ft north of the main wreckage. It contained the vertical stabilizer, horizontal stabilizer, and elevator, which remained relatively intact. Several pieces of the structure below and forward of the horizontal stabilizer were found fragmented and separated from the rest of the tail assembly. The rudder and its hinges were found completely separated from and about 600 ft to the east of the vertical stabilizer. The two-seat, low-wing, experimental amateur-built airplane was manufactured in 1998 and powered by a Ly-Con AEIO-360-EXP, 238-horspower, four-cylinder engine driving an MT-Propeller two-blade, constant-speed propeller. The airplane was constructed of glass-fiber-reinforced epoxy, carbon-fiber-reinforced epoxy, and glass fiber and carbon fiber honeycomb sandwich panels. The fuselage was of a monocoque-type design. The airplane's most recent condition inspection was completed on March 25, 2015, at which time the airplane had accumulated 400 total hours in service. At the time of the accident, the airplane had accumulated about 48 hours since that inspection. On August 28, 2015, at 1407 eastern daylight time, an experimental amateur-built Giles G-202, N18FJ, was destroyed when it collided with terrain after experiencing an in-flight separation of the tail section during a practice aerobatic demonstration flight at Stewart International Airport (SWF), Newburgh, New York. The commercial pilot was fatally injured. The airplane was privately owned and was operated under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight, which was operating over runway 09/27 at the time of the accident. The purpose of the flight was to practice for an air show routine scheduled to be performed the following day at the New York Air Show. Witness statements and video recordings indicated that the airplane had performed 4 or 5 maneuvers and was about 5 minutes into the routine when the tail suddenly separated from the fuselage. At that time, the airplane was performing a left aileron roll while climbing at an approximate 45° angle. Several witness photographs and video recordings showed the airplane's fuselage twisting toward the left relative to the tail section before the tail section completely separated from the fuselage. The elevator and rudder appeared to be at or near their neutral positions at the time of separation. No abrupt flight control deflections occurred and no parts were seen separating from the airplane in the moments before the separation. The airplane subsequently impacted a grass field about 1,100 ft south of the runway centerline. The engine was running continuously until impact. Airport personnel recovered the tail section and debris from the north side of the runway, about 1,800 ft north of the main wreckage. The pilot was wearing a parachute for the flight. Review of the on-board video recording revealed that he did not attempt to open the airplane's canopy after the tail separated. The five-point seatbelt harness buckle was found fastened securely at the accident site. The airplane was not equipped with a conventional flight recorder, nor was it required to be. It was equipped with 3 video cameras. Video and audio were recovered from one camera. Follow-up examinations of the airframe revealed that the horizontal and vertical stabilizer had fractured from the remainder of the airplane in several locations: along the lower side of the horizontal stabilizer at the bonds between the skin panels and the "L" shaped flanges attaching the lower side of the horizontal stabilizer to the vertical stabilizer and fuselage skin panels, at the bond between the upper end of the banjo bulkhead and the lower skin of the horizontal stabilizer, through the fuselage skin forward of the vertical stabilizer, and through the vertical spar at the aft end of the vertical stabilizer (See Figure 1). Figure 1 - Horizontal and Vertical Stabilizer Joint Further examination revealed that the bonds between both right and left "L" flanges, which were constructed of glass-fiber-reinforced cloth and epoxy, were fractured from their mating surfaces on both legs of the "L" (the legs mating to the lower horizontal stabilizer skin and to the fuselage skin) in several locations. The bond between the banjo bulkhead and the horizontal stabilizer lower skin was fractured entirely. Most of the bond surface area in all locations exhibited evidence of fiber pullout and resin transfer; however, two areas that showed limited fiber or resin transfer were located on the left flange where it had mated to the lower skin of the horizontal stabilizer near its leading edge. A study examining all the fractures in the tail area determined that the first fracture to occur was the bond fracture in the left flange at the bottom of the horizontal stabilizer near its leading edge. The fracture features in this area were consistent with tensile opening, which translates to a relative upward motion of the left side of the horizontal stabilizer (or, relative downward motion of the lower fuselage skin on the left side of the tail). There was no clear evidence of progressive crack growth on any of the fracture surfaces. Some contact damage on the fracture surface was present. A finite element model was constructed to evaluate areas of concentrated stress in the tail, specifically in the areas of the "L" fla