Four Red Herrings, Float Switch Failure and a Case of Multiple Failure Scenarios

摘要

In the course of a failure investigation, the Analyst may be faced with multiple failure scenarios including those promoted by the manufacturer, suggested by the customer, uncovered by the investigation, or assumed by the analyst. This case study covers investigation of fuel float switches in which evidence was found to support several proposed, but ultimately misleading, failure scenarios. The true root cause, solder creep, was determined only after a reexamination of preliminary failure mode assumptions. Proper root cause diagnosis underscored the danger of assumptions and the value of both expert knowledge and broad based experience in failure analysis to ensure a proper conclusion.