If you have a Superior Air Parts Inc. model IO-360/O-360 or a Lycoming 360-series under the cowling, you’ve likely been watching the proposed AD for the crankshaft used in some of these engines. The Superior Air Parts crankshaft is installed as an original-equipment component, and also as a PMA replacement part on affected Lycoming engines. As anticipated, the final ruling is an AD (AD-2020-25), and is effective Jan. 15, 2021.
The AD was prompted by three crankshaft assembly failures in training aircraft that resulted in loss of power and immediate or emergency landings. The FAA has determined that the crankshaft failures were the result of a manufacturing problem that dates back to production runs in 2012 and 2015. According to the FAA, the build process induced an excessive residual layer of iron nitrate that formed on the crankshaft assembly. The layer of iron nitrate becomes brittle and can ultimately lead to spalling and fatigue cracking of the crank, says the FAA. The FAA determined that all three engine failures were the result of this fatigue cracking.