According to FAA airworthiness records, the airplane was issued a special airworthiness certificate on Aug. 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 in Climax, North Carolina.
According to the airplane owner, who was also the builder of the airplane and was not on board the airplane for the accident flight, there were several gaps in engine operation between 2021 and 2023. Review of an airplane log found entries denoting ground engine operation and flight activity from Oct. 5, 2021, through Aug. 27, 2022. A total of 8.6 hours was logged, and within those hours three hours were flight hours logged in 2021.
According to 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 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 100LL 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.
According to the pilot’s operating handbook (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.
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: “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 three-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 the surviving pilot, on the morning of the accident, he flew one solo flight and returned to the airport. Shortly after, the other pilot boarded the airplane for a flight to perform aerodynamic stall testing.
The airplane had 12 gallons of fuel on board, which was 93 octane fuel the pilot purchased from a gas station near the departure airport.
The surviving pilot reported that the left-seat pilot was the pilot flying and the takeoff from Runway 35 was normal. The airplane climbed to 400 feet above ground level, where the engine RPM dropped, the engine lost partial power, and the pilot made two left turns to fly southbound over the highway parallel to the runway (US Highway 421).
While flying over the highway, both fuel pumps were on, and the surviving pilot reported that he was adjusting the mixture and throttle. The engine continued to produce partial power while they overflew the highway, however an overpass bridge was located ahead of the airplane, along with a semi-truck that had stopped under the overpass. Additionally, multiple powerlines spanned across the highway.
The surviving pilot reported that he knew they would not be able to gain sufficient altitude to fly above the powerlines nor fly under the overpass due to the semi-truck, so they attempted to fly below the powerlines, but above the overpass.
During this maneuvering, the airplane crashed into the overpass, and then hit terrain. A post-impact fire ignited after the crash.
Motorists pulled the right-seat pilot, who was already partially outside the cockpit, away from the wreckage area. The pilot in the left seat died in the crash.
Multiple witnesses on the highway reported observing the airplane flying low over the highway. One witness described that she first saw the airplane about 50 feet above ground level over the northbound lanes near the airport, then observed the airplane cross over the grass median to fly over the southbound lanes.
Another witness observed the airplane flying low over the southbound lanes. She observed the airplane enter a sharp turn and “tilt sideways” immediately before striking the overpass and stated that the “wing tips were straight up in the air.” She could not recall hearing engine noise, or whether the propeller was turning.
A post-crash 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.
Probable Cause: 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.
NTSB Identification: 107039
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This April 2023 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
