Primary finding
Probable cause
A loss of engine power due to a loss of compression in one of the engine’s two cylinders.
Investigator assessment
Analysis narrative
The pilot reported that a few minutes after takeoff, during the initial climb, the airplane’s two-stroke engine began to slowly lose power. The pilot attempted to restart the engine but was unsuccessful. He elected to make a forced landing in small field, resulting in substantial damage to both of the airplane’s wing struts. Postaccident examination of the engine revealed that one of the engine’s two cylinders had no compression. It is likely that this lack of compression resulted in the loss of engine power reported by the pilot during the accident flight. Additionally, during the examination, a zip tie was found secured around the fuel line that provided fuel for that cylinder in a way that reduced its interior diameter. It is possible that the reduced diameter of the fuel line could have resulted in less fuel reaching the cylinder during high power operation, and that it was operating in an excessively lean condition. Operation in this state could have damaged the cylinder and resulted in the lack of compression observed during the engine examination. It could not be determined when the zip-tie was installed on the fuel line, though entries in the airplane’s maintenance logs indicated that its last condition inspection was completed about three months before the accident.
Source record
Factual narrative
On September 1, 2023, at 0910 eastern daylight time, an experimental amateur-built Challenger II, N2480Y, was substantially damaged when it was involved in an accident near Moultonborough, New Hampshire. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, during takeoff and initial climb, the engine was producing full power without anomalies. Then, while still in the climb, the engine gradually sustained a total loss of power. The pilot attempted to make two engine restarts but was unsuccessful. The pilot performed a forced landing in a field, resulting in substantial damage to both left and right wing struts. A postaccident examination of the two-cylinder, two-stroke engine found that the airplane contained between 7 and 10 gallons of fuel with no contamination. There was evidence of spark from all of the ignition leads, and all four spark plugs were gapped within recommended specifications. The engine’s crankshaft rotated when force was applied to the propeller with no discrepancies noted. The engine contained adequate oil. The cylinders were checked for compression and the cylinder closest to the magneto had no compression. A fuel line leading to the cylinder was found with a zip-tie secured to it that reduced the interior circumference of the fuel line. According to the airplane’s maintenance logbooks, the fuel lines were installed in March 2013 and inspected in June 2019. A condition inspection of the engine was completed in June 2023, with a total time of 564.7 hours. It is unknown when the zip-tie was placed around the fuel line.