WPR14FA369

The failure of the right wing under normal race loads due to an improper repair of the right wing spar that reduced its structural strength following a previous landing accident.

The one-of-a-kind airplane designed specifically for air racing was participating in a practice air race session. Photographic and video evidence showed that the airplane entered the race course while accelerating and descending as the pilot was banking left around the back side of the race course. While passing one of the race pylons, the outboard portion of the right wing failed, and the airplane began rolling to the right followed by the empennage fragmenting and separating from the fuselage as the airplane descended into the ground. Based on the available evidence, the outboard right wing separation was the initiating failure and the empennage separation was a secondary failure. The outboard portion of right wing was reconstructed using the pieces found in the initial debris path. The reconstruction revealed that the right wing forward box spar fractured at the inboard end of a splice repair to the right wing spar in an area where the upper and lower spar caps transitioned from a singular rectangular cross section to two smaller rectangular finger sections. The scarf joints on each finger were also fractured through the adhesive with no evidence of wood grain failure on either side of the scarf areas. Typically, failure of a bonded wood joint should occur within the wood grain adjacent to the bond area if the adhesive has been properly prepared and applied. The accident airplane was involved in a landing accident about 30 months before the accident that substantially damaged the right wing. The wing was reportedly removed from the airplane and repaired by the original designer. No information existed on the repair, no logbook entry was made for the repair, and no requirement for documenting any repairs to the airplane existed in the operating limitations. It is likely that the right wing spar repair was not done in accordance with the approved methods in the Federal Aviation Administration Advisory Circular (AC) 43.13-1B, thus the strength of the wing in the area of the repair was reduced. Aircraft maintenance records contained entries related to cracking in the right and left wing lower skins. Personnel working on the airplane during the air races reported that the cracking was located in the area aft of the forward spar near the main landing gear trunnions, which was well inboard of the area where the right wing failed. The investigation determined that these cracks did not contribute to the accident. The morning of the accident, the pilot attempted a practice flight; however, he pulled off the course shortly after entering the course due to an excessive vibration. The race crew determined that the pilot had encountered the rev-limiting function on the engine control unit. The pilot reported to another pilot that he thought the airplane was going to shake itself apart during the event. It is possible that the airframe vibrations induced by the engine could have affected the spar repair on the right wing. Further, the airplane's high speed, high g-loads, and left bank produced wing loads sufficient to fail the right wing forward spar at the location of a previous repair. Even though the airplane was likely not being operated outside the original design envelope at the time of the right wing failure, the reduced strength of the repair led to the wing's failure.

The Reno/Stead Airport is a non-towered airport that operates in class G airspace. The airport features two runways, 14/32, a 9,000-foot long and 150-foot wide asphalt runway, and 8/26, a 7,608-foot long and 150-foot wide asphalt runway. The reported airport elevation is 5,050 feet. The crew chief reported that the airplane suffered a collapse of both main landing gear during a landing at Hollister Municipal Airport, Hollister, California, on March 11, 2012, following a test flight. According to information provided by the FAA, the pilot was unable to get the right main landing gear in the down and locked position. During the landing, the right main landing gear collapsed and the left main landing gear broke off the airplane. The airplane sustained damage to both main landing gear and doors, the right wing, air scoop, and propeller. Photographs provided to the investigation showed significant damage to the right wing upper and lower skins and leading edge. Damage to the internal wing structure could not be quantified from the photographs. According to the crew chief, the wing was removed from the airplane and sent to the designer for repair. The airplane was flown to an airshow in Oshkosh, Wisconsin, in July, 2013. During the return flight, the accident pilot reported to the crew chief that the pitch characteristics of the airplane were abnormal. Inspection of the airplane found the bulkhead where the elevator quadrant was attached had fractured from its mounts. The damage was repaired and documented in the airframe logbook. The crew chief reported that the cracks in the right and left wing lower skins were located in a similar location on each wing, aft of the forward spar in the area of the main landing gear trunnions. The cracks were reportedly repaired in accordance with Federal Aviation Administration Advisory Circular (AC) 43.13-1B. In a telephone interview with the designer and builder of the airplane, he stated that the wing was a one- piece construction at original manufacture. The forward spar was a box spar and was designed to carry all of the wing bending loads. The spar caps were of one-piece design with no splices along the length. The rear spar and wing skins carried the wing torsion loads. He informed the investigation team that the design drawings had been lost. He recalled repairing the right wing after the landing gear failure in March, 2012 but only recalled repairing the leading edge and leading edge ribs on the right wing. He did not recall any spar damage on the right wing. No engineering data was generated for the repair and he stated it was all performed in accordance with AC 43.13-1B. The accident pilot performed a practice flight on the NCAR course during the morning of September 8, 2014, and called a mayday during the flight. The pilot reported to the crew chief that the airplane began to shake when he applied power. The crew examined the data from the engine control unit and found that the rev limiter had engaged as the rpm increased to the set limit of about 6,000 rpm. A normal inspection of the airplane by the crew did not reveal any discrepancies. The pilot reported to another Sport Class pilot that he thought the airplane was going to come apart it was shaking so badly during the event. FAA AC 43.13-1B "contains methods, techniques, and practices acceptable to the Administrator for the inspection and repair of nonpressurized areas of civil aircraft, only when there are no manufacturer repair or maintenance instructions." Chapter 1 - Wood Structure, Section 4 - Repairs, contains information on the design of scarf joints and the repair of wing spars. Figure 1-8 in the AC provides information on the method to splice box spar flanges. The AC states that reinforcement plates must be used on all scarf repairs to spars and provides minimum dimensions for scarf joints. The information in Figure 8 shows that for box spar flanges, the scarf should have a minimum slope of 15 times the thickness of the flange being spliced. Reinforcement plates should be at least 1/2t thick and 21t long where t represents the thickness of the flange being spliced. The investigation team planned to reexamine the wreckage after obtaining the logbooks and other additional information. Unfortunately, the insurance company disposed of the wreckage without the knowledge or approval of the NTSB. The Washoe County Medical Examiner conducted an autopsy on the pilot on September 9, 2014. The medical examiner determined that the cause of death was "blunt force injuries." The FAA's Civil Aeromedical Institute (CAMI) in Oklahoma City, Oklahoma, performed toxicology tests on the pilot. According to CAMI's report, volatiles, and drugs were tested, and had negative results. Examination of the accident site by representatives from the National Transportation Safety Board (NTSB) revealed that wreckage debris was scatted between race pylons 5 and 6 of the outer race course. All major structural components of the airplane were located within the approximate 4,000 foot long debris path. All debris remained within the predetermined safety areas for the outer race course. There were three distinct debris fields located in the sagebrush covered terrain. The first debris field along the route of flight contained the outboard portion of the right wing, fragmented portions of the right aileron, the aileron bellcrank, and numerous pieces of wing skin and internal wing structure. The second debris field along the route of flight contained the right and left horizontal stabilizers, right and left elevators, the fragmented vertical stabilizer and rudder, pieces of the empennage structure, and several pieces of the acrylic canopy. The third debris field along the route of flight contained the initial impact crater and the highly fragmented remains of the airplane, engine and propeller. There was no evidence of a post-crash fire. The entire airplane was accounted for in the three debris fields. The debris from the first and second debris fields was collected separately for further examination. The g-meter was found in the third debris field. One pointer was situated just above zero, one was situated at -4.5 and one was situated at -4.0. The Advanced Flight Systems AF-4500 multifunction display (MFD) screen and main body were recovered separated in the third debris field. The Pectel SQ6 Engine Control Unit (ECU) was also recovered in the third debris field. The MFD and ECU were sent to the NTSB Vehicle Reorders Laboratory for download and analysis. See the NTSB Onboard Electronic Devices Specialist's Factual Report in the public docket for the details of the investigation. Further examination of the right wing was conducted by the Airworthiness Group. The group reconstructed the outboard right wing using the pieces recovered in the first debris field. The largest intact piece of right wing included the forward portion of rib 9, rib 10, rib 11, the wingtip outboard of rib 11, the forward spar outboard of rib 10, and portions of the upper and lower skins. Most of the outboard 50 inches of right wing was conclusively identified in the recovered debris from the inboard end of the aileron to the wing tip. The outboard 50 inches of upper wing skin was identified and reconstructed between the forward and rear spars. The leading edge structure forward of the forward spar and inboard of rib 9 (about 32 inches inboard of the wing tip) was not conclusively identified. The forward portion of rib 9 was intact forward of the forward spar. The aft portion of rib 9 between the forward and rear spars was reconstructed. The nose of the leading edge between rib 9 and about 9 inches inboard of the wing tip was not conclusively identified. Most of the lower wing skin from rib 9 outboard was identified and reconstructed between the forward end of the nose ribs and the rear spar. A triangular section between ribs 9 and 10 and forward of the forward spar was not conc