ERA25LA215

The pilot stated that shortly after takeoff the engine made a popping noise with a noticeable loss of engine thrust. The rpm gauge indicated “0” but the propeller continued to rotate. The pilot declared a MAYDAY and made a forced landing in the ocean. Postaccident examination of the engine revealed that the crankshaft gear bolt was about 1/8th inch out from being seated on the crankshaft gear. The crankshaft gear bolt head was rounded, and the bottom threads of the bolt were damaged. The crankshaft gear was removed, and the alignment dowel was found sheared. Four teeth were also sheared from the oil adapter idler gear. Metallurgical examination of the fractured components determined they had fractured from shear overstress. Per the engine maintenance log, at the last annual inspection (about 6 months prior to the accident), the engine had had accrued about 650 hours since it was overhauled. There were no entries in the maintenance records to indicate the crankshaft bolt had been removed, inspected, or modified since the engine had been overhauled. Based on the available information it is likely that when the engine was overhauled, the crankshaft gear bolt was not properly seated against the crankshaft gear, which resulted in the crankshaft gear eventually disengaging from the accessory gears leading to a total loss of engine power.

On June 1, 2025, at 1028 eastern daylight time, a Piper PA32-300 airplane, N2242Z, was involved in an accident near Branford, Connecticut. The private pilot/owner and the passenger were not injured. The flight was conducted as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot departed from Bridgeport/Sikorsky Airport (BDR), Bridgeport, Connecticut, about 1014, and was en route to Block Island State Airport (BID), Block Island, Rhode Island. The pilot stated that all engine indications were normal as he climbed and leveled off at 3,000 ft mean sea level (msl) over Long Island Sound. Shortly after, the engine made a popping noise “similar to a backfire” with a noticeable loss of engine thrust. The pilot noted the engine rpm gauge went to “0” but the propeller continued to rotate. He declared a MAYDAY and made a forced landing in the water south of Branford, Connecticut. The airplane was equipped with a Garmin G3X, which recorded flight and engine data. Review of data obtained from that device revealed that after takeoff, the airplane was headed eastbound at an airspeed of about 120 knots, at 3,000 ft msl. At 1023, the engine speed dropped from 2,390 rpm to 520 rpm, and to 0 rpm 2 seconds later. The engine speed remained 0 rpm for the rest of the flight. All the other engine parameters corresponded to the loss of engine power consecutively, including a drop of exhaust gas temperature, oil pressure, and fuel flow rate. The last recorded data point was at 1028, just before the airplane landed in the water. The airplane wreckage was recovered and taken to a secure facility for further examination. Both wings had been removed, and substantial damage was observed on the lower fuselage. The engine and its two-blade propeller remained securely attached to the airframe. Evidence of corrosion was noted from exposure to saltwater. The rocker box covers were removed, and no anomalies were noted. The crankshaft was rotated when force was applied to the propeller. Thumb compressions were established on all cylinders, but valve action movement was not observed on any of the cylinders. The engine was removed from the airframe to facilitate further examination. The accessory section of the engine was removed, and the crankshaft gear bolt was found about 1/8th inch out from the seated position. The safety lock plate washer was installed. The crankshaft gear bolt head was rounded. The crankshaft gear bolt was removed, and the bottom threads of the bolt were damaged. The crankshaft gear was removed, and the alignment dowel was sheared. Four teeth were sheared from the oil adapter idler gear and found in the oil sump. Per Lycoming, the head of the crankshaft gear bolt appeared to be marked 2247, which indicated the bolt was a Lycoming STD-2247, the applicable crankshaft gear bolt for this engine. The oil pump idler gear, remnants of four teeth from the oil pump idler gear, the oil pump drive shaft, and the crankshaft gear with crankshaft gearbolt, and the crankshaft alignment dowel pin were examined by the NTSB Materials Laboratory. The broken components from the engine, the crankshaft alignment dowel pin, and four teeth from the oil pump idler gear were determined to have fractured from shear overstress. All the other components exhibited damage consistent with rotational wear or contact damage with adjacent components. There were no features suggesting pre-existing damage in the fractured components. The electronic tachometer was damaged from saltwater exposure, and a reading was not attainable. A review of the engine maintenance records revealed the engine was last overhauled on August 27, 2018. The last annual inspection prior to the accident was completed on January 16, 2025, and the engine had accrued 648.9 hours since overhaul. There were no entries in the records to indicate that the crankshaft gear bolt had been removed/inspected/modified since the engine had been overhauled. According to the Textron Lycoming Direct Drive Overhaul Manual, Section 7-65, Crankshaft Gear; "Assemble the gear to the crankshaft using both a new lockplate and bolt. The correct bolt, lockplate and dowel for each gear are shown in Table 7-4. Tighten the bolt to 125 inch lbs. torque, then with a hammer and brass drift, tap lightly around the pilot flange of the gear and listen for sharp solid sounds from the hammer blows that would indicate that the gear is seated against the crankshaft. As a check on seating against the crankshaft, attempt to insert a pointed .001 inch thick feeler gage or shim stock between the gear and crankshaft at each of the three scallops. The .001 feeler gage, or any smaller feeler gage, must fit between the two surfaces at any location. (.001 feeler gage is used as an indicator, however there must be no clearance between crankshaft and gear.) Retighten the gear attaching bolt to the proper torque. Tighten the 5/16 inch bolt to 204 inch-pound torque or the 1/2 inch bolt to 660 inch-pound torque. Measure the clearance between the O.D. of the gear flange and the pilot I.D. of the crankshaft. There should not be more than .0005 inch clearance at any point. Bend the lockplate against the bolt head." On January 23, 2003, Lycoming issued a mandatory service bulletin (SB475C) for crankshaft gear modification and assembly procedures that in part 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." Step 6 of the procedures described the assembly of the gear to the crankshaft using a new lockplate and bolt, "Assemble the gear to the crankshaft using both a new lockplate and bolt. Refer to Figure 6. The correct bolt,lockplate and dowel for each gear are shown in Table 2. Tighten the bolt to 125 in.-lbs. torque, then with a hammer and brass drift, tap lightly around the pilot flange of the gear and listen for sharp solid sounds from the hammer blows that would indicate that the gear is seated against the crankshaft. As a check on the seating against the crankshaft, attempt to insert a pointed .001 inch thick feeler gage or shim stock between the gear and crankshaft at each of the three scallops. The .001 feeler gage, or any smaller feeler gage, must NOT fit between the two surfaces at any location. (.001 feeler gage is used as an indicator, however, there must be no clearance between crankshaft and gear.) Retighten the gear attaching bolt to the proper torque. Tighten the 5/16 inch bolt to 204 in.-lbs. torque or the 1 1/2 inch bolt to 660 in.-lbs. torque. Measure the clearance between the O.D. of the gear flange and the pilot I.D. of the crankshaft. There should not be more than .0005 inch clearance at any point." On September 12, 2016, Lycoming issued supplement No. 1 to the mandatory service bulletin that provided an alternate method of compliance to Service Bulletin No. 475C if the crankshaft gear was replaced rather than modified.