WPR24LA240

The pilot reported that after climbing to the airplane’s cruise altitude of about 9,000 ft mean sea level (msl), he configured the airplane to maintain straight and level flight and adjusted the mixture control to “rich of peak.” Shortly after leaning the fuel mixture, the engine began to run rough and a pronounced vibration began. The pilot made a 180° turn to the south, after which he observed a loss of oil pressure and the engine subsequently lost total power. During the forced landing, the airplane encountered a ditch and nosed over. Postaccident examination of the engine revealed about a 3-inch hole in the top of the crankcase above the No. 2 cylinder. Further examination revealed that the No. 1 piston had separated from the connecting rod wrist pin and fragments of the piston were present in the engine oil sump. The No. 2 piston connecting rod broke free from the crankshaft at the bearings, end cap, retention bolts, and nuts. Each of the cylinders and pistons displayed detonation signatures. There was no evidence of an induction leak on the No. 1 cylinder. While the pilot reported that his normal procedure was to operate the engine during cruise flight with a fuel to air mixture that was “rich of peak,” the procedure that the pilot described was more consistent with a lean mixture configuration as described by Section II in the cruise checklist of the manufacturer’s Pilot Operating Handbook. Given the pilot’s consistent and long-term operating procedure, it is likely that the fuel to air mixture was too lean and resulted in the explosive ignition of the fuel to air mixture within the No. 1 cylinder’s combustion chamber. The damage observed to the engine’s remaining pistons and cylinders was consistent with detonation signatures, resulting in a failure of the No. 1 piston and the No. 2 piston connecting rod, and the subsequent total loss of engine power.

On July 13, 2024, about 0749 mountain daylight time, a Cessna 182B airplane, N2617G, sustained substantial damage when it was involved in an accident near Soldier, Idaho. The pilot and passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he departed on a cross-country flight from Buhl Municipal Airport (U03), Buhl, Idaho, to Smiley Creek Airstrip (U87), Smiley Creek, Idaho. He stated that after climbing to his desired cruise altitude, about 9,000 ft msl, the manifold pressure was about 18 inches of mercury. He reported that his normal operating procedure to establish cruise flight was to trim the airplane for straight and level flight, adjust the manifold pressure to 18 inches of mercury, adjust the mixture to “rich of peak,” and close the cowl flaps. His technique for adjusting the mixture was to pull the mixture control knob out until the engine presented a noticeable roughness, then turn the mixture control knob about three or four rotations to the right to increase the air to fuel mixture until the engine roughness subsided. Section II of the airplane manufacturer’s Pilot Operating Handbook included a checklist to establish cruise flight operations. Steps 1 through 3 instructed the pilot to select a cruise power setting and stabilize and trim the airplane. Step 4 of the checklist instructed pilots to lean the mixture by pulling the control knob out until the engine becomes rough and then enrich the mixture slightly beyond this point. The pilot reported that about 29 minutes into the flight, while over mountainous terrain, the engine began running rough and a pronounced engine vibration began, but the engine oil temperature and pressure remained within normal operating limits. He immediately made a 180° turn to the south and observed that the engine oil pressure had decreased below normal operating parameters, followed by a total loss of engine power. The pilot initiated a forced landing to a grass-covered field. During the landing roll, the airplane encountered a ditch, the landing gear sheared off, and the airplane nosed over, sustaining substantial damage to the left wing lift strut. Postaccident examination of the engine revealed about a 3-inch hole in the top of the crankcase above the No. 2 cylinder. A lighted borescope was inserted into the spark plug orifice of each cylinder and revealed that the No. 1 piston was not present; however, fragments of the piston were found in the engine oil sump. The No. 2 piston connecting rod had failed at the crankshaft and was free of the bearings, retention bolts, nuts, and end cap. Each of the cylinders was removed from the crankcase, and detonation signatures were observed throughout, in the form of cylinder head pitting, damage to the piston skirts, piston crown pitting, and shiny metallic fragments observed on the cylinder heads and piston crowns. No evidence of an induction leak was observed.Magneto to engine timing was not confirmed due to impact damage to the left and right magnetos. The airplane underwent an annual inspection on April 26, 2024. The airplane had accumulated about 10.6 hours since the annual inspection, and the engine had accumulated about 1,044.79 hours since being overhauled. The FAA’s Pilot’s Book of Aeronautical Knowledge states, in part: An overly lean mixture causes detonation, which may result in rough engine operation, overheating, and/or a loss of power. It further states: Detonation is an uncontrolled, explosive ignition of the fuel-air mixture within the cylinder’s combustion chamber. It causes excessive temperatures and pressures which, if not corrected, can quickly lead to failure of the piston, cylinder, or valves. In less severe cases, detonation causes engine overheating, roughness, or loss of power. Detonation is characterized by high cylinder head temperatures and is most likely to occur when operating at high power settings. Common operational causes of detonation are: - Use of a lower fuel grade than that specified by the aircraft manufacturer - Operation of the engine with extremely high manifold pressures in conjunction with low rpm - Operation of the engine at high power settings with an excessively lean mixture.