On April 21, 1999, a local school bus fleet administrator contacted ODI alleging that one of their buses was involved in an engine run-away incident.After inspecting the bus and finding the governor link separated from the track bar due to a retaining rivet failure, ODI interviewed the driver.She claimed she was able to stop the bus after shifting to neutral but still had no control over engine speed which remained quite high.In fact, her loss of engine control was complete...she could not even shut it down.Ultimately it quit due to overheating.We found a relevant Caterpillar Technical Information Bulletin dated April 22, 1998 concerning Loose Rivet in Rack Control Assembly.The rivet involved in the school bus incident and Caterpillar's bulletin are one and the same.However, the bulletin mentions nothing about the potential for engine run-away due to a rivet failure.According to the company, the apparent cause for the rivet failure was compromised quality control of the peening process during manufacture of the control assembly.Evaluation of failure data demonstrates the quality control problem began in April 1996.Caterpillar implemented a new peening process on March 25, 1998 and no rivet failures have occurred since.This investigation was closed on June 23, 1999 with Caterpillar's safety recall.