DFW05FA188 · Cessna 310Q

The 1,500-hour airline transport rated pilot had just departed a 6,305-foot-long runway when, based on a viewing of security camera footage, a puff of white smoke exiting the back of the right engine shortly after the airplane became airborne. The airplane then began a right turn and flew on a westerly heading at a low altitude before it disappeared behind a tree line. A witness saw the airplane as it was in a right turn toward the north. He thought the airplane was going to land on a closed highway, but the nose of the airplane dropped and the airplane cartwheeled on the grass median west of the road. Examination of the right engine revealed that the crankshaft gear had failed due to a fatigue fracture in one of the teeth. The fatigue emanated from the pressure face of the tooth and intersected another crack emanating from the non-pressure face of the tooth, thereby producing separation of the tooth from the rim. Near the origin, post-fracture damage prevented the ability to determine if the crack initiated in fatigue or if a crack propagated in overstress through the case and then continued propagating through the core in fatigue. Upon completion of the materials examination it was evident that the microstructure of the gear was inadequate and more research into the manufacturing process was required. A review of manufacturing records indicated that approximately 2,400 crankshaft gears were made from the same batch of material as the accident gears, and were heat-treated in two groups. A review of the heat treatment records confirmed that furnace temperatures during the hardening step in each heat-treating process were not high enough to fully austenitize the material. Furthermore, the quantity and orientation of gears loaded in the furnace were greater when compared to other jobs completed for TCM. In addition, initial data from a test load similar to that used in the heat-treating process from the accident serial number gear, indicated that under these conditions, the gears might not have been fully equilibrated at temperature during the hardening step. As a result, TCM manufactured several other gears at different hardnesses and conducted failure testing to see if they could reproduce a similar failure. Even though some of the hardness levels were well below TCM standards, they were unable to produce a similar failure. In addition, there was evidence to suggest that the gear teeth may have been exposed to an excessive load at some point during its operation. The cause of the gear tooth failure could not be determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset