On December 12, 2022, about 2005 central standard time, a Mooney M20K, N231GZ, was substantially damaged when it was involved in an accident near Addison, Texas. The pilot and passenger were seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The flight originated at the Abilene Regional Airport (ABI) in Abilene, Texas, and was enroute to Addison Airport (ADS) in Addison, Texas. The pilot reported being vectored for an instrument landing system approach to runway 16 at ADS when the engine lost all power and the propeller automatically feathered. He stated that, after an unsuccessful attempt to restart the engine, he aligned the airplane with a road for a forced landing. During the approach to the road, the airplane impacted a power pole, which resulted in substantial damage to the wings and fuselage. A postimpact fire ensued. During a postaccident examination, 12 of the camshaft gear teeth were found either broken or missing. Six of the gear teeth were found in the oil sump. The aircraft owner reported that the maintenance logbooks were in the airplane at the time of the accident and were burned, so a review of engine maintenance could not be performed. In 2005 Continental Motors issued critical service bulletin (SB) CSB05-8C; in 2018, that SB was superseded by CSB05-8D. The SB pertained to certain camshaft gear part numbers on certain engines, including the TSIO-520-NB17N and the camshaft gear (part number 655516) installed on the accident airplane. The SB stated that during the airplane’s next 100 hour or annual inspection, the camshaft gear should be replaced with the newer model, part number 656818, which increased the camshaft gear face circumference by .060 inches to prevent the possibility of camshaft gear tooth failure. At the time of the accident, the accident airplane still had the old camshaft gear installed. Although compliance with the SB is not mandatory for Part 91 operations, laboratory analysis confirmed that the gear teeth fractured due to fatigue cracks, which were consistent with the description from the SB.