Spartanburg, SC, USA
N8580N
PIPER PA-28-235
The pilot reported that the preflight inspection, run-up, and takeoff were routine. During the initial climb, about 600 ft above ground level (agl), a boom was heard and the engine rpm dropped to zero. The pilot completed a forced landing on a city street. On final approach to the road, the airplane struck live powerlines; however, the landing was completed without further incident. After landing, the pilot exited the airplane and deployed a fire extinguisher toward smoke emanating from the engine and cowling area. The power line strike resulted in substantial damage to the rudder. Examination of the engine revealed that the crankshaft gear partially separated from the crankshaft. The crankshaft gear bolt was partially backed out from its normal position and a few threads were stripped. The safety clip remained attached. The crankshaft alignment dowel pin had sheared. This condition prevented crankshaft continuity to the engine’s accessory drive gears and resulted in the total loss of engine power. Metallurgical examination of the fractured crankshaft gear alignment dowel revealed a shear overstress fracture. The shaft of the crankshaft drive gear bolt was bent near the start of the threads, the last threads were flattened, and the end face of the bolt was smeared. An airworthiness directive (AD), in addition to an engine manufacturer service bulletin, required inspection and replacement of any worn alignment dowel and crankshaft drive gear bolt; however, the maintenance procedure was only required to be completed during engine overhaul, after a propeller strike, or whenever the crankshaft gear was removed. Although there were multiple maintenance logbook entries in the several years preceding the accident noting compliance with the propeller strike AD, there was no record that the AD/service bulletin (SB) was complied with in full (to include an inspection of the crankshaft drive gear, bolt, dowel pin, and replacement as warranted). There was also no record of a propeller strike. The left magneto’s exterior casing was found fractured and partially rotated from its normal attachment points. Further disassembly of the unit found that its bearings rotated freely. In addition, the fracture surface of the left magneto gear tooth and the fracture surfaces of the left idler gear had features consistent with overstress separation. There was no evidence of recent maintenance to either magneto. It is likely that the left magneto damage and left idler gear damage was not an originating event that contributed to the loss of engine power based upon these factors. The engine displayed sooting and thermal damage. The propeller blade tip exhibited black marks on the front side and a small section of the tip showed evidence of melting and erosion. The damage was consistent with electrical arcing damage as a result of striking powerlines during the emergency landing, which likely caused a fire in the engine compartment during the landing or landing roll, which was extinguished by the pilot with a fire extinguisher after exiting the airplane.
On October 23, 2022, about 1700 eastern daylight time, a Piper PA28-235 airplane, N8580N, was substantially damaged when it was involved in an accident near the Spartanburg Downtown Memorial Airport (SPA), Spartanburg, South Carolina. The private pilot and three passengers were not injured. The airplane was operated as a personal flight conducted under the provisions of Title 14 Code of Federal Regulations Part 91. The pilot reported that the preflight inspection, run-up, and takeoff were routine. During the initial climb, about 600 ft agl, he heard a “boom,” the engine rpm dropped to zero, and the engine lost all power. He immediately established best glide airspeed and completed a forced landing on a city street. On final approach to the road, the airplane struck powerlines but touched down without further incident. Following the landing, the pilot exited the airplane and deployed a fire extinguisher toward smoke emanating from the engine and cowling area. The power line strike resulted in substantial damage to the rudder. Examination of the engine revealed no visible impact related damage; however, sooting and thermal damage was observed to the engine, cowling, and some engine accessories. One propeller blade tip exhibited black marks on the front side and a small section of the tip showed evidence of melting and erosion, consistent with arc damage. Valvetrain continuity was established with the camshaft; however, crankshaft continuity was not observed. The accessory section of the engine was removed and the crankshaft gear was found partially separated from the crankshaft. The crankshaft gear bolt was partially backed out from its normal position and a few threads were stripped. The safety clip remained attached. The crankshaft alignment dowel pin had sheared. The right magneto was attached to the accessory section. It was rotated and spark was noted on all cut leads. The left magneto’s exterior casing was fractured and partially rotated from its normal attachment points. It had a bent drive shaft that could not be rotated and its idler gear was missing a few teeth. The left and right idler gears, the left magneto and drive gear, crankshaft gear and bolt were sent to the National Transportation Safety Board (NTSB) Materials Laboratory for metallurgical examination. The left magneto was dissembled and examined. The internal components displayed multiple areas of rotational damage; however, once disassembled to its bearings, the unit rotated freely by hand. The fracture surface of the separated left magneto gear tooth and the fracture surfaces of the left idler gear had features consistent with overstress separation. The metallurgical examination found that the shaft of the crankshaft drive gear bolt was bent near the start of the threads, the last threads were flattened, and the end face of the bolt was smeared. The end face was completely obscured by secondary smearing damage and no discernible features were noted to determine if any of the bolt had separated or was missing. The fracture surface of the crankshaft drive gear alignment dowel pin was in-line with the outer flat of the flange and was mostly unobscured, with only a small area of secondary smearing damage. The visible fracture surface features on the dowel pin were consistent with shear overstress separation. Figure 1 provides an overview of the crankshaft drive gear, its bolt, and a close up view of the alignment dowel pin that remained installed within the crankshaft gear. Figure 1: Drawing of the rear end view of the crankshaft drive gear and NTSB photographs from the materials laboratory factual report. In January 2003, the engine manufacturer published Mandatory Service Bulletin (SB) No. 475C, Crankshaft Gear Modification and Assembly Procedures, which applied to the accident engine in certain circumstances. In 2004, the Federal Aviation Administration issued an airworthiness directive (AD) for propeller strikes (AD 2004-10-14) in which the compliance section referred to SB 475C. The AD/SB was to be complied with, “During overhaul, after a propeller strike, or whenever crankshaft gear removal is required.” The SB further stated: Damage to the crankshaft gear and the counterbored recess in the rear of the crankshaft, as well as badly worn or broken gear alignment dowels are the result of improper assembly techniques or the reuse of worn or damaged parts during reassembly. Since a failure of the gear or the gear attaching parts would result in complete engine stoppage, the proper inspection and reassembly of these parts is very important. The procedures described in the following steps are mandatory. The most recent annual inspection occurred on February 15, 2022, and the airplane had flown 34 hours since this inspection. On January 2, 2021, the maintenance records reflected that the AD for a propeller strike (AD 2004-10-14) was noted as complied with as part of a 100-hour inspection. The mechanic who completed the maintenance reported that he was not aware of any propeller strike. He reported that it was his normal practice to record that this AD was completed on every annual or 100-hour inspection, due to the broad definition of a propeller strike. He further clarified that no work or inspection was performed to the crankshaft gear bolt, and he saw no evidence that a propeller strike had occurred. On July 6, 2015, an annual inspection endorsement noted compliance with AD 2004-10-14; however, the endorsement did not note whether any components on the crankshaft drive gear were inspected or replaced. On December 17, 2015, the left and right magnetos were replaced with new magnetos. This was the most recent magneto replacement. The engine was last overhauled on May 2, 2003, 1569.49 hours before the accident. The SB 475C had been issued before this overhaul, and the maintenance endorsement noted that all applicable service bulletins had been complied; however, a specific reference to No. 475C was not stated in the endorsement. According to the owner of the airplane, who was the accident pilot, he purchased the airplane in 2015 and was not aware of any propeller strikes with the airplane.
A partial separation of the crankshaft gear/bolt, which resulted in a total loss of engine power.
Source: NTSB Aviation Accident Database
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