ERA23FA188

The airplane owner/builder’s inappropriate use of a lower grade fuel than that required by the airplane and engine operations manual, which resulted in engine detonation and the degradation and eventual obliteration of the Nos. 1 and 2 cylinder spark plug electrode tips. Contributing to the outcome was the pilots’ decision to continue flight at low altitude following a partial loss of engine power instead of performing an immediate precautionary landing, which resulted in collision with an overpass and terrain.

Two commercial pilots departed for a local flight in the experimental amateur-built airplane that was undergoing Phase 1 flight testing. The purpose of the flight was to perform aerodynamic stall testing. Earlier in the day, the right-seat pilot had completed a solo flight. Upon returning to the airport, the left-seat pilot boarded the airplane and they taxied for takeoff. During the climb, about 400 ft above ground level, the airplane sustained an abrupt partial loss of engine power. The airplane immediately stopped climbing and the pilot entered a left turn, then turned left again to fly over a highway that paralleled the departure runway. The pilots attempted to troubleshoot the partial loss of engine power by adjusting the throttle and mixture, and by ensuring that both fuel pumps were on, but were unable to restore engine power. The airplane continued toward an overpass, under which a semi-truck was parked, and near which powerlines spanned across the highway. The pilots attempted to fly under the powerlines and over the overpass, but entered an extreme bank angle and impacted the overpass before coming to rest inverted below it. A post-crash fire ignited immediately. The right-seat pilot was pulled from the wreckage by motorists; the left-seat pilot was fatally injured. Examination of the engine found that the Nos. 1 and 2 cylinder spark plug electrode tips were obliterated. The Nos. 3 and 4 cylinder spark plug electrode tips remained intact, but were found blackened. There was no evidence that any of the spark plugs had sustained impact-related damage. A bench test of the spark plugs found that the Nos. 1 and 2 plugs would produce a spark at low compression, but would extinguish under the higher compression levels produced during normal engine operation. The Nos. 3 and 4 cylinder spark plugs produced normal spark at the bench test’s maximum compression. It is likely that the partial loss of engine power was due to the damaged Nos. 1 and 2 spark plug electrode tips. The owner/builder of the airplane stated that he used low-grade 87 octane automotive fuel with the engine in its first 9 hours of operation about two years before the accident. The engine manufacturer required that the engine be operated with at least 89 octane automotive fuel or higher grade. The manual and engine manufacturer further reported that using low grades of automotive fuel could result in engine detonation and/or catastrophic failure. The operations manual further stated that, when stored for 3 months or longer, the airplane should be stored with 100 low lead aviation fuel. The airplane owner reported that the airplane sat idle for nearly two years, during which occasional engine run-ups were performed, and that the fuel onboard during this time was automotive fuel with a fuel preservative/additive. Despite the surviving pilot reporting that he fueled the airplane with 93 octane automotive fuel for his recent flight activity and the accident flight, it is likely that the estimated first 9 hours of engine operation with the lower grade of fuel, and old automotive fuel, likely contributed to the degradation and ultimate failure of the Nos. 1 and 2 spark plug electrodes during the accident flight. Although the engine lacked other signatures of detonation, it is likely that the spark plug damage was due to detonation occurring at some point in the airplane’s 20 total hours of engine operation. There was no evidence that the spark plugs had been inspected or replaced during the required annual condition inspection seven months before the accident. According to the pilot’s operating handbook, the landing distance was 525 ft. During the pilots’ engine troubleshooting, they overflew more than 4,000 ft of a multilane highway with a wide grass median. Had either pilot decided to make an immediate precautionary off-airport landing either on the grass median or the highway, rather than continuing the engine troubleshooting at low altitude, the conflict with powerlines and the collision with the overpass likely could have been prevented. It is also likely that the partial loss of engine power, rather than a total loss of power, exacerbated the confusion and indecision by both pilots on whether an immediate precautionary landing should be made. The engine examination findings and testing of the spark plugs supported a scenario in which the engine likely would continue to run, but could not produce sufficient power to climb. Toxicology testing for the fatally injured left-seat pilot detected Carboxyhemoglobin at 15%, consistent with smoke inhalation after the accident, glucose, and acetaminophen. The testing was negative for ethanol.

According to the surviving pilot, he had flown the airplane 6 hours, and the pilot seated in the left seat, who was the pilot flying, had 8 hours in the airplane. According to Federal Aviation Administration (FAA) airworthiness records, the airplane was issued a special airworthiness certificate on August 30, 2021. The airworthiness certificate outlined multiple limitations during Phase 1 flight testing. One limitation required a total of 40 hours to be flown within certain prescribed geographic areas, which included the departure airport. According to the airplane owner, who was also the builder of the airplane and was not onboard the airplane for the accident flight, there were several-month gaps in engine operation between 2021 and 2023. Review of an airplane log found entries denoting ground engine operation and flight activity from October 5, 2021, through August 27, 2022. A total of 8.6 hours was logged, and within those hours 3 hours were flight hours logged in 2021. According to the log and the owner, he did not fly the airplane in 2022 or 2023. The right-seat pilot reported that he and the other pilot flew about 14 hours in the airplane, which resulted in about 22 hours of total flight time for the airplane. According to the owner, in March 2023, he and the right-seat pilot had an agreement to complete the remainder of the 40 hours required to complete Phase 1 flight testing. The airplane owner reported that he recalled there being about 1/2 of a tank of fuel onboard the airplane for the more than a year that it did not fly. He recalled that he added an additive to the tank to help preserve the automotive gas. He recalled performing an engine run-up in October 2022 and did not experience any issues. The airplane owner further reported that he used automotive gasoline with the engine. He reported specifically that he used 87 grade octane and that the engine was a small car engine from a Honda Fit, and he “felt comfortable” using the “lower grade” 87. He never used 100 low lead (100LL) aviation fuel with the airplane. The owner also reported that he never had any discussions with either accident pilot on what type of fuel they should use for the test flights. Pilot’s Operating Handbook The pilot’s operating handbook (POH) stated that the airplane’s aerodynamic stall speed with flaps extended was 41 knots and 45 knots with flaps retracted. The published landing distance was estimated to be 525 ft at maximum gross weight. The fuel capacity was 19.8 gallons. According to the POH, approved fuel types were 89 octane or higher automotive fuel with 10% ethanol as a maximum. It further stated that 100LL could be used when automotive fuel was not available. Engine The engine was a 110-horsepower fuel-injected Viking Aircraft Engine, Model 110. Viking Aircraft Engines produce experimental aircraft engines from originally manufactured Honda Fit car engines. The Viking Aircraft Engines operating handbook, Chapter 5, Engine Operation, stated to use only 100LL when 90 or higher octane fuel is not available. The handbook further stated: FUEL: These are high compression, high performance engines! Use 89 or higher octane fuel. Up to 10% ethanol is permitted. Never run lower grade fuels! It can and will destroy your engine. The manual further stated, “the engine should never be left with auto type fuel in the fuel rail or fuel pumps for longer than 3 month intervals. The approved storage fuel is 100LL aviation fuel. 100LL was used to test run the engine at the factory, prior to shipping.” According to a representative with Viking Aircraft Engines, the normal compression for a Viking 110 engine was 180 to 210 psi. The spark plugs to be used were NGK brand Iridium Spark Plugs. The representative further reported that the engine may exhibit detonation should 87 octane be used. Maintenance Records Review of the airframe logbook revealed that the most recent condition inspection was recorded on September 1, 2022; however, the endorsement was not signed. The engine and propeller logbook were not located; however, they were later shipped by the airplane owner to the NTSB for review. The engine logbook contained one entry, dated July 8, 2021, denoting that the engine was inspected in accordance with 14 CFR Part 43 Appendix D. The inspection was signed by the airplane owner/builder. There were no other entries noted in the engine logbook. The propeller logbook contained one entry, dated July 8, 2021, denoting that the propeller was inspected in accordance with Part 43 Appendix D. The inspection was signed by the airplane owner/builder. There were no other entries noted in the propeller logbook. There were no entries to indicate that the spark plugs had been inspected or replaced since 2021. According to the autopsy report for the left-seat pilot, from the Office of the Chief Medical Examiner, North Carolina Department of Health and Human Services, the pilot’s cause of death was blunt force injury of the leg, thermal injury, and inhalation of products of combustion. Toxicology testing for the fatally injured left-seat pilot, performed by the FAA Forensic Sciences Laboratory, detected Carboxyhemoglobin at 15%, consistent with smoke inhalation after the accident, glucose, and acetaminophen. The testing was negative for ethanol. Toxicology testing was not performed on the surviving pilot. The airplane came to rest inverted, the wreckage was fragmented, and was located in a compact area. All major portions of the airframe were located at the accident site. The engine was co-located with the cockpit and firewall debris. A postcrash fire consumed significant portions of the fuselage, cockpit, and left wing. Flight control continuity was confirmed from the cockpit to the rudder and elevator surfaces. Multiple breaks consistent with impact-related forces and severe thermal damage were observed within the aileron control push-pull rods. All cockpit switches, instrumentation, the center fuel tank, and non-volatile memory were destroyed by the postimpact fire (see figure 3). Figure 3 - Overview of the accident site as viewed from the overpass the airplane impacted. Note the powerlines above the overpass, which spanned across the entire highway from east to west. The engine sustained extensive thermal damage. The engine examination revealed no evidence of catastrophic failure. The gear reduction box rotated freely and normally with the propeller hub when removed from the engine. The oil filter was free of contaminants. The main fuel line on the engine was secure but was thermally damaged. The chain tensioner was intact and had melted. The camshaft gear, when moved by hand, moved all the rocker arms and valves. The main crankshaft bearings were intact and displayed clean oil signatures. The pistons and valves were intact and displayed normal combustion signatures. The composite, three-bladed propeller WAS manufactured by Warp Drive. All three blades splintered from the propeller hub. Two of the blades were located in the debris. One blade exhibited a leading edge gouge. Spark Plugs The NGK brand iridium spark plugs were found securely installed and were free of impact damage. When the spark plugs were removed and examined, the Nos. 1 and 2 cylinder spark plug ground electrode tips were found obliterated and the remainder of the electrodes on both spark plugs exhibited blackening. The Nos. 3 and 4 cylinder spark plugs were blackened; however, their electrode tips remained intact. Spark Plug Test The spark plugs were tested with bench test equipment. The test equipment used compressed air to simulate engine compression. The Nos. 1 and 2 spark plugs exhibited a spark around 60 to 70 psi, but with compression at 70 to 80 psi both spark plugs would immediately lose their continuous spark and would extinguish. The Nos. 3 and 4 spark plugs operated normally and produced a continuous spark throughout a range of low pressure up