CEN24LA155

The pilot was conducting a cross-country flight when the engine rpm slightly decreased. He attempted to troubleshoot but the engine surged before it lost all power. The pilot then prepared for a forced landing to a field. During the landing roll, the airplane impacted trees at the edge of a down-sloping, wet field. The airplane came to rest upright and sustained substantial damage to the stabilator, fuselage, and both wings. Postaccident examination of the engine revealed that the engine crankshaft had fractured in two locations due to fatigue. The fatigue crack initiation sites were located near rotational wear bands. The inner diameter surfaces and edge faces of two sets of the main bearing journals exhibited severe gouging, cracking, and material spalling, consistent with rotational abrasive wear. Based on the damage, the degraded bearings likely prevented sufficient lubrication, leading to excessive heating and scoring that helped initiate fatigue cracking of the crankshaft. The engine was most recently overhauled about 28 years and 2,439 flight hours before the accident. The manufacturer’s recommended time between overhaul (TBO) interval was 2,000 flight hours or 12 years, whichever occurred first. Although not required for Part 91 operations, following the manufacturer’s recommended overhaul procedures likely would have prevented the bearing failure and subsequent loss of engine power.

On April 11, 2024, about 0825 central daylight time, a Piper PA-32, N651ED, was substantially damaged when it was involved in an accident near Sullivan, Missouri. The passenger sustained minor injuries and the pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight. According to the pilot, about 0600, the flight departed Rochester International Airport, Rochester, Minnesota, after a preflight check and normal engine runup. The flight then continued towards Kirk Field Airport (PGR), Paragould, Arkansas. About 2 hours after takeoff, the pilot noticed a slight drop in rpm and began troubleshooting the engine issue by turning on the auxiliary fuel pump, switching fuel tanks, and adjusting the fuel mixture. The pilot was unable to restore engine power and, about 2 minutes after the pilot noticed the initial drop in rpm, the engine surged and then lost all power. The pilot told the air traffic controller that the airplane had a loss of engine power and prepared for a forced landing to a field. During the landing roll, the airplane impacted trees at the edge of a down-sloping, wet field. The airplane came to rest upright and sustained substantial damage to the stabilator, fuselage, and both wings. A postaccident review of the airplane’s engine monitor data revealed an increase in oil temperature and a decrease in oil pressure before the total loss of engine rpm, as shown in the figure below. An initial engine examination at the accident site revealed a bent No. 3 cylinder intake valve pushrod tube and a crack in the engine case. Figure. Plots of recorded engine data (engine speed, oil temperature, oil pressure) Postaccident examination of the engine and its accessories revealed little to no impact damage except for a crack in the right engine case above the No. 3 cylinder and bent pushrods on cylinder No. 3. The engine mount exhibited minor impact damage consistent with damage from the nose gear during the accident sequence. The 3-bladed propeller was found attached to the engine crankshaft with one of the three blades having a small bend toward the tip. The other two blades remained undamaged. The engine crankshaft was fractured in two areas. Examination of the crankshaft, a portion of a connecting rod, and the main bearing halves by the NTSB Materials Laboratory indicated that the crankshaft fractured through the webs between the second main (M2) and the third crankpin (C3) journals, and between the fourth crankpin (C4) and third main (M3) journal positions. The examination revealed that the fractures were from fatigue cracking that initiated at multiple sites along the radius between the bearing journals and the webs. The fatigue crack initiation sites were located near rotational wear bands. The bearings exhibited wear patterns consistent with rotational contact between the faying surfaces on both sides. The inner diameter surfaces and edge faces of two sets of the main bearingjournals exhibited severe gouging, cracking, and material spalling, consistent with rotational abrasive wear. In addition, the cylinder No. 4 connecting rod exhibited a fracture from reverse-bending fatigue cracking that initiated at each flange face, and the associated bearing exhibited severe spalling and wear on the interior surface. According to maintenance records, the engine was rebuilt in 1986, then later overhauled in 1997 due to a crack in the case. The bearing part numbers and build dates on the accident engine were consistent with having been replaced in the latter overhaul. Lycoming Service Instruction 1512, Main and Connecting Rod Bearing Upgrade, issued in 2004, lists those bearing part numbers as obsolete, superseded by improved bearings. The instruction, “requires the use of the upgraded bearing whenever new bearings are installed;” however, it was issued about 7 years after their installation. Lycoming Engine Service Instruction 1009BE, Time Between Overhaul (TBO) Schedules, stated that the TBO for the accident engine was 2,000 hours of operation or 12 years (whichever occurred first). Federal aviation regulations do not require 14 CFR Part 91 operations to follow manufacturer service instructions. The airplane’s most recent annual inspection was completed on August 24, 2023, about 7 months before the accident. At the time of the inspection, the engine had accrued about 2353.7 hours of operation since the overhaul in 1997. An oil sample was sent for routine analysis as part of the inspection; the results of the analysis were normal.