CEN23LA165

The pilot stated the engine lost power as 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 the engine. 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 2 additional engine starts, which also resulted in the engine quitting above 4,000 rpm. The pilot then noticed white smoke emitting from the engine compartment. A fire ensued that resulted in substantial damage to the motorglider. Postaccident examination of the engine revealed that the right carburetor bowl cover was attached to the carburetor bowl but the carburetor bowl cover retention clip was not in its secure position on the bowl cover. The left carburetor bowl cover was missing and was not recovered; it most likely fell out of the motorglider or was dislodged from the airplane when the fire was being extinguished. An unsecured bowl cover would have allowed fuel to leak onto hot exhaust pipes, resulting in a fire. Neither carburetor had optional carburetor drip trays installed to mitigate the risk of an engine fire from fuel leaking onto the engine exhaust from the carburetors by directing it away from the exhaust and overboard, which may have prevented the accident. Engine logbook entries showed that the carburetor bowl covers were removed during recent maintenance. It is likely that the covers were not properly reinstalled during that maintenance.

On April 13, 2023, about 1200 central daylight time, a Pipistrel LSA SRL Sinus, N413EK, was involved in an accident near Iron Mountain, Michigan. The motorglider sustained substantial damage. The private pilot and a passenger were uninjured. The motorglider was operated under Title 14 Code of Federal Regulations (CFR) Part 91 as a personal flight. The pilot stated 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 the engine. The engine ran smoothly and with no roughness for about one minute. When engine power was increased above 4,000 rpm, the engine lost power again. The pilot performed 2 additional engine starts, which also resulted in the engine quitting above 4,000 rpm. The pilot then noticed thin white smoke from the engine compartment. A fire ensued that resulted in substantial damage to the motorglider. The fire was extinguished by airport firefighting when the engine was sprayed with a firefighting agent. Postaccident examination of the motorglider revealed the left aft side of the engine and bottom engine cowl displayed greater thermal damage than the right side engine and engine cowl. Thermal damage of the bottom left side of the engine cowl extended almost the full length, as viewed from nose to tail, and about mid-length of its right side. The left carburetor, as viewed from the aircraft tail to nose, was present and separated from its induction tube rubber flange due to thermal damage separation. The carburetor induction tube mating clamp was present and unbroken. The carburetor control cables were attached and secure. The carburetor bowl cover was not present, and the carburetor bowl retention clip was intact, unbroken, and secured to the carburetor body. The carburetor bowl cover was not found. The carburetor bowl displayed soot and the metal components within the bowl did not display melting. The right carburetor, as viewed from the aircraft tail to nose, was present, attached, and secured, to its induction tube rubber flange. The carburetor control cables were attached and secure. The carburetor bowl cover was attached to the carburetor bowl, and the carburetor bowl retention clip was not positioned in its secure position onto the bowl. The retention clip was intact, unbroken, and secured to the carburetor body. The left and right carburetors did not have carburetor drip trays installed, which have a part number of 874300 for Rotax 912 and 914 engines. The drip trays are optional unless the engine is ordered from Rotax with an airbox. Pipistrel did not order the engine with a Rotax airbox. The drip trays mitigate the risk of an engine fire from fuel leaking onto the engine exhaust from the carburetors by directing it away from the exhaust and overboard. The engine logbooks showed that the most recent maintenance entries for the engine were made by an independent RotaxMaintenance Technician (iRMT), who completed 9 Series Service and 9 Series Maintenance training. His iRMT certification had an expiration date of October 21. 2023. To be eligible to perform carburetor overhauls, one must complete the Rotax 9 series overhaul course, which is restricted to designated and approved facilities. The mechanic was not certified to perform carburetor overhauls; however, the mechanic was authorized to perform maintenance tasks on carburetors such as changing floats, balancing/synchronizing them, changing jets, and conducting 200-hour service inspections, among others. 14 CFR Part 91.417(a)(1)(ii) requires the date maintenance was completed to be included in aircraft logbook entries. The second to last engine logbook entry wasdated December 6, 2022, and cited a tachometer time of 224.7 and a Hobbs time of 309.7 hours. The entry stated that the [carburetor] float bowls were removed, and the floats were replaced. The last engine logbook entry was undated and cited a tachometer time of 226.5 and a Hobbs time of 314. The entry stated that the carburetors were dissembled and inspected, and components were replaced with components included in 71 889 534 overhaul kits. The entry stated that the next overhaul is due at a tachometer time of 400 hours. There is no specific overhaul time limit mentioned in any of the Rotax manuals for carburetor overhaul. Kit 71 889 534 is referred by Rotax as a Maintenance Set Carburetor. There is no specific overhaul time limit mentioned in any of the Rotax manuals. Rotax Maintenance Manual (Heavy), section 73-00-10, Page 22, under the "Insert Float Chamber and Floats" section, instruction #4 specifies fixing the float chamber with the spring clip [retention clip]. Since 2018 Pipistrel has maintained an occurrence database that contains occurrences reported directly to Pipistrel (e.g., employees, operators, pilots, etc.) and accident investigations that were communicated as per Annex 13. There is no other reference of a fire related to carburetor fuel leakage inside the database before the accident involving N413EK.