Addison, TX, USA
N231GZ
MOONEY AIRCRAFT CORP. M20K
The airplane lost all engine power during a precision instrument approach for landing to the destination airport. After the pilot was unsuccessful in attempting to restart the engine, he performed an off-airport landing to a road, during which the airplane struck a pole and a postcrash fire ensued. There was substantial damage to the wings and fuselage. Postaccident examination revealed that about 12 of the camshaft gear teeth were fractured due to fatigue cracking. The airplane engine’s camshaft gear part numbers were affected by the engine manufacturer’s service bulletin (SB) for camshaft gear tooth fracture or cracks of the teeth. The SB called for the replacement of the camshaft gear with a newer model. The intent of the SB was to eliminate the possibility of camshaft gear tooth fracture, resulting in power loss or in-flight shutdown; compliance with the SB is not mandatory for Part 91 operations. Based upon the camshaft gear part numbers, the SB was not complied with but likely would have addressed the fatigue failure of the camshaft gear teeth. The maintenance records for the airplane were destroyed in the postimpact fire and could not be examined.
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.
The fatigue failure of the engine’s camshaft gear teeth which resulted in a loss of all engine power. Contributing to the accident was the non-compliance with the engine manufacturer’s recommended service bulletin.
Source: NTSB Aviation Accident Database
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