ERA24FA160

The pilot/builder’s modifications of the motorglider’s engine, which resulted in an excessively lean fuel air mixture, preignition, piston failure, and a subsequent total loss of engine power during the initial climb. Contributing to the outcome was the pilot’s failure to maintain airspeed and his exceedance of the motorglider’s critical angle of attack following the loss of engine power, which resulted in an aerodynamic stall/spin at an altitude too low to recover.

The kit manufacturer manager reported that the accident flight was the pilot/builder’s second flight in the motorglider, the first of which was two days before the accident. A witness at the airport reported seeing the pilot taxi for takeoff and that the engine sounded “a bit rough,” but due to the nature of the small two-stroke engine he was not concerned. The witness reported that the motorglider took off and, when it reached about 100 ft to 150 ft above ground level (agl), the engine sputtered then went silent. Video footage showed that when the motorglider was about midfield, it turned right, then left, then pitched up before the left wing dropped and the motorglider began a near-vertical left rotating descent to ground impact consistent with a low-altitude stall and spin. Postaccident examination of the motorglider revealed no evidence of any preimpact mechanical malfunctions or failures of the flight controls or airframe that would have precluded normal operation. Examination of the engine revealed that the original airbox had been replaced with an unrestricted cone-type air filter. The main carburetor jet had also been replaced with a smaller jet, which would have resulted in the engine running slightly lean (the builder had reported that he thought the engine had been running too rich). Additionally, a hole was noted in the center of the engine’s single piston. A metallurgical examination of the piston revealed light gray deposits covering portions of the crown surface around the hole. The piston crown had features consistent with pre-ignition damage. This damage was likely the result of an excessively lean mixture due to the unrestricted air intake and smaller main jet. The hole in the piston would have resulted in a total loss of engine power. The distance from the accident site to the end of the available grass area was about 1,300 ft. The kit manufacturer reported that the motorglider’s typical landing roll was about 200 ft or less. Had the pilot aggressively lowered the nose of the motorglider to maintain airspeed following the loss of engine power, it is likely that he could have avoided the low altitude aerodynamic stall/spin and landed within the remaining available runway.

A review of the pilot’s logbooks showed that he received his first instructional flight in a glider on September 17, 1972. From the date of his first flight until the date of the accident the pilot had accumulated 118.6 hours of flight time over 283 flights. The pilot was issued a private pilot certificate with a glider rating on April 26, 2018, and was endorsed for self-launch operations on February 15, 2024. A former flight instructor for the pilot reported that he and the pilot performed 5 flights from April 26, 2021, to May 17, 2021, in a Pipistrel Alpha motorglider and that the pilot came to the flight school to receive training as he was building his own motorglider. The flight instructor stated that the long commute and unfavorable weather conditions led the pilot to pause his training. The instructor reported that “considerable practice was still required before considering solo flights.” The last flight instructor to fly with the accident pilot was the flight instructor who gave the pilot his endorsement for self-launch. The instructor reported the pilot’s “aeronautical knowledge, demeanor, and skills were exemplary; he was a model student and a pleasure to fly with. He arrived highly proficient, well-trained, and needed very minimal additional training from me.” He also reported that during the training they performed an aborted takeoff maneuver, where the flight instructor reduced power to idle at an altitude about 100 ft agl to simulate an engine failure on takeoff and the pilot was expected to land on the remaining runway available. He went on to say that during the aborted takeoff training, he had to prompt the pilot “to aggressively lower the nose with loss of engine power to keep airspeed.” FAA airworthiness records showed that the motorglider was issued an experimental amateur-built airworthiness certificate on October 31, 2023. This motorglider was only the second to be built from the kit provided by Aeromarine LSA and was equipped with a two-stroke Polini Thor 303DS single-cylinder engine. The kit manufacturer manager, who flew the motorglider 3 days before the accident, reported that the normal takeoff roll was between 200 ft and 250 ft and that the landing roll was about 200 ft or less. According to the autopsy report from the Office of the District Medical Examiner 10th Judicial Circuit of Florida, the pilot’s cause of death was blunt force trauma, and the manner was accident. The FAA Forensic Sciences Laboratory performed toxicological testing of postmortem specimens from the pilot. Sacubitril and desethyl sacubitril were found in aortic blood and urine. Sacubitril is a prescription medication available as a combination drug with valsartan, which was also detected in this case. This combination drug is used in the treatment of chronic heart failure. Desethyl sacubitril is a metabolite of sacubitril. Sacubitril is not typically impairing. Toxicological testing also found Tamsulosin, Loratadine, Desloratadine, and Carvedilol in aortic blood and urine. Tamsulosin (Flomax) is an alpha blocker used to treat benign prostate hyperplasia and is acceptable for pilots. Loratadine (Claritin) and the metabolite Desloratadine are non-prescription non-sedating antihistamine used to treat allergies. Loratadine is acceptable for pilots. Carvedilol (Coreg) is a beta-blocker used to treat high blood pressure and is acceptable for pilots. On April 2, 2024, at 1038 eastern daylight time, an experimental amateur-built Merlin Lite, N622PC, was substantially damaged when it was involved in an accident near Mulberry, Florida. The private pilot was fatally injured. The motorglider was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The manager of the company who the pilot/builder had bought the kit from reported that the pilot flew the motorglider two days before the accident and to his knowledge that was the only flight the pilot completed in the motorglider. He had spoken with the pilot after the flight and the pilot told him he had practiced “crow hops.” An article in the September 2022 issue of EAA Sport Aviation magazine stated the idea behind a crow hop was “…you lift the airplane off the runway, cruise a few feet forward, and then land.” A witness saw the motorglider taxi toward the end of runway 14 at South Lakeland Airport (X49), Lakeland, Florida, and that the engine sounded “a bit rough but it is only a small 2-stroke so I didn’t think it was unusual.” He reported that when he heard the motorglider at a high power setting, he and another witness turned to watch the takeoff. Multiple witnesses reported that when the motorglider was about 100 to 150 ft agl the engine went silent. Review of a surveillance video revealed that after liftoff, as the motorglider was about midfield, it turned right, then left, then pitched up before the left wing dropped and the motorglider began a near-vertical left rotating descent until impacting the ground. The motorglider came to rest about 1,500 ft from the threshold of runway 14. The distance from the accident site to the end of the available grass area was about 1,300 ft. The fuselage displayed crushing and buckling in multiple locations. The empennage was partially separated and remained attached to the fuselage by the rudder and elevator control cables, control rods and the bottom skin. The vertical stabilizer, rudder, horizontal stabilizer, elevator, and elevator trim tab remained attached at all attachment points and were undamaged. The electric trim was visually in a neutral position. The right wing remained attached to the fuselage at all attachment points. The leading edge was impact crushed aft along the full length. The right aileron remained attached to the wing at all attachment points and exhibited impact damage. The right flap was in the up position and remained attached to the wing at all attachment points. The left wing remained attached to the fuselage at all attachment points. The left wing was impact fractured outboard of the flap and remained attached through the left aileron control rod. The outboard two thirds of the left wing’s leading edge exhibited impact crushing aft. The left aileron remained attached at all attachment points and the inboard trailing edge corner exhibited impact damage. The left flap was in the up position and remained attached at all attachment points. Continuity was confirmed from all flight control surfaces to the flight controls in the cockpit. The engine had broken free from the airframe and displayed impact damage signatures. The propeller flange was impact separated from the propeller driveshaft. The cylinder head and cylinder sleeve were removed from the engine. There was a quarter-sized hole in the middle of the piston and the piston material around the hole had been eroded. The cylinder sleeve displayed minor scoring of the cylinder walls and the cylinder head was undamaged. The intake and exhaust ports of the cylinder were unobstructed and displayed normal operating signatures. The piston head, cylinder sleeve, and cylinder head were examined at the National Transportation Safety Board Materials Laboratory. The examination found the piston had a hole in the middle of the crown, and the surrounding areas had light gray deposits covering portions of the crown surface. The remaining area of the piston crown and interior surfaces of the cylinder head appeared to be free of heavy combustion deposits. Machining marks and partial vibro-peen markings were visible on the piston crown. The piston crown had features consistent with pre-ignition damage. Pre-ignition occurs when an ignition source such as an overheated spark plug tip, glowing hot carbon or lead deposits in the combustion chamber, or a burned exhaust valve prematurely ignites the fuel/air mixture in the cylinder during the combustion cycle. Additional possible causes for pre-ignition include use of unsuitab