ERA24LA152

**This report was modified on April 29, 2025. Please see the public docket for this investigation to view the original report.** The pilot reported that, after starting the engine, it “sounded slightly rough” and then it ran smoothly “after a few seconds.” She continued with her engine run up and magneto check, neither of which indicated any anomalies. The pilot stated that, during the takeoff roll, the engine indications were “green,” but she was not sure of the static rpm achieved, and the airspeed was increasing “slightly slower than normal.” After reaching a rotation speed of 55 kts, the pilot rotated, but noticed during the initial climb that the engine was not producing full power, and the airspeed was low. She further characterized the engine performance as constant but sluggish. The pilot lowered the nose to prevent an aerodynamic stall and attempted a forced landing, during which the airplane impacted trees and came to rest inverted. Postaccident examination of the airplane revealed substantial damage to both wings, the fuselage, and the engine mounts. The examination of the fuel injector assembly found a combination of fuel and oil had contaminated between the air diaphragm and the regulator cover. A service bulletin from the fuel injector manufacturer stated that with this type of contamination, an engine could exhibit “gradually deteriorating idle, difficulty starting and/or cold engine acceleration performance.” With the exception of magneto timing that was 3 degrees advance of the engine’s specification, no evidence of any preimpact mechanical malfunction or failure was observed with the engine or its subsystems. Based on the available information, it is likely that the contamination of the fuel injector assembly resulted in the lack of engine performance described by the pilot.

On March 24, 2024, at 1330 eastern daylight time, a Cessna 172S, N863AU, was substantially damaged when it was involved in an accident near Opelika, Alabama. The private pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that she completed a preflight inspection of the airplane with no anomalies noted. During engine start, the engine “sounded slightly rough,” and then it ran smoothly “after a few seconds.” During the engine run-up, there were no unusual indications, and the magneto check was normal. During the takeoff roll, the engine indications were “green,” and airspeed was increasing “slightly slower than normal.” The pilot reported that she was not sure of the exact static rpm the engine reached during the takeoff roll but that it did not feel as though the engine was producing the normal amount of power. Upon reaching a rotation speed of 55 kts, the pilot rotated and began the initial climb. As the initial climb progressed, the pilot noticed the airspeed was not accelerating normally, staying about 60 to 65 kts, and the engine was only producing about 1,700-1,750 rpm, despite the throttle and mixture controls being full forward. The pilot subsequently lowered the airplane’s nose and flew toward a forced landing area. She reported that she did not see the engine rpm raise and then drop during the flight and characterized the engine performance as constant but sluggish. The airplane impacted trees and came to rest inverted during the forced landing. Postaccident photographs showed substantial damage to both wings, the fuselage, and the engine mount. A postaccident examination of the airplane found continuity of the engine crankshaft and valvetrain. Compression and suction were observed on all cylinders in the correct firing order when the crankshaft was rotated. Both magnetos remained secure to their fittings on the accessory housing and the timing was found to be 28° before top dead center. The engine data tag showed that the timing for the engine should be 25° before top dead center. The fuel injector assembly was removed from the engine and disassembled. The examination of the fuel injector revealed a combination of fuel/oil contamination between the air diaphragm (Avstar part number AV 2538295) and the regulator cover (part number AV 2577194). Service bulletin AFS-SB10 from the fuel injector manufacturer states, “There have been occasional reports of servo equipped engines that exhibit one or more of the following characteristics - gradually deteriorating idle, difficulty starting and/or cold engine acceleration performance. These engines may have the servo mounted in an updraft, or nearly updraft configuration. Close inspection of the servo may reveal oily contaminant in the bore of the servo that is green/blue in color. It is also possible for this contaminant to migrate into the air section of the regulator.”