Accident Overview
On April 13, 2023, at about 1200 central daylight time, a Pipistrel LSA SRL Sinus, registration N413EK, was involved in an accident near Iron Mountain, Michigan. The motorglider sustained substantial damage. The private pilot and a passenger were uninjured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Engine and Fire
The pilot reported that the engine lost power when he increased power for takeoff. The engine could not be restarted, and the airplane was pushed off the runway onto a taxiway. The pilot allowed the engine to cool and then restarted it. The engine ran smoothly for about one minute. When engine power was increased above 4,000 rpm, the engine lost power again. The pilot performed two additional engine starts, both resulting in the engine quitting above 4,000 rpm. The pilot then noticed thin white smoke from the engine compartment. A fire ensued, resulting in substantial damage to the motorglider. The fire was extinguished by airport firefighting personnel, who sprayed the engine with a firefighting agent.
Postaccident Examination
Examination of the motorglider revealed greater thermal damage on the left aft side of the engine and bottom engine cowl compared to the right side. Thermal damage on the bottom left side of the engine cowl extended almost the full length, while damage on the right side was about mid-length. The left carburetor, as viewed from the tail, was separated from its induction tube rubber flange due to thermal damage. The carburetor induction tube mating clamp was present and unbroken. The carburetor bowl cover was missing, and the bowl retention clip was intact and secured to the carburetor body. The carburetor bowl showed soot, and metal components within the bowl did not exhibit melting. The right carburetor was attached and secured to its induction tube rubber flange, with control cables attached. The right carburetor bowl cover was attached, but the retention clip was not positioned in its secure position onto the bowl; the clip was intact and secured to the carburetor body. Neither carburetor had drip trays installed (part number 874300 for Rotax 912 and 914 engines). The drip trays are optional unless the engine is ordered with an airbox; Pipistrel did not order the engine with a Rotax airbox. Drip trays are designed to mitigate fire risk from fuel leaking onto the exhaust.
Maintenance Records
The engine logbooks showed that the most recent maintenance was performed by an independent Rotax Maintenance Technician (iRMT) who had completed 9 Series Service and 9 Series Maintenance training. His iRMT certification was valid until October 21, 2023. The mechanic was not certified to perform carburetor overhauls, as that requires completing the Rotax 9 series overhaul course, which is restricted to designated facilities. However, he was authorized to perform maintenance tasks such as changing floats, balancing/synchronizing carburetors, changing jets, and conducting 200-hour service inspections. The second-to-last engine logbook entry was dated December 6, 2022, with tachometer time 224.7 and Hobbs time 309.7 hours. That entry stated that the float bowls were removed and floats were replaced. The last engine logbook entry was undated, with tachometer time 226.5 and Hobbs time 314 hours. It stated that the carburetors were disassembled and inspected, and components were replaced with components from overhaul kits (71 889 534). The entry noted that the next overhaul was due at tachometer time 400 hours. Rotax manuals do not specify an overhaul time limit for carburetors. Kit 71 889 534 is referred to as a Maintenance Set Carburetor. The Rotax Maintenance Manual (Heavy), section 73-00-10, page 22, under "Insert Float Chamber and Floats," instruction #4 specifies fixing the float chamber with the spring clip (retention clip). Since 2018, Pipistrel has maintained an occurrence database that includes reports from employees, operators, pilots, and accident investigations. No other reference of a fire related to carburetor fuel leakage was found in the database before the accident involving N413EK.