This is a NAVAL POSTGRADUATE SCHOOL MONTEREY CA report procured by the Pentagon and made available for public release. It has been reproduced in the best form available to the Pentagon. It is not spiral-bound, but rather assembled with Velobinding in a soft, white linen cover. The Storming Media report number is A124783. The abstract provided by the Pentagon follows: The purpose of this thesis is to study the usability an upgraded Maintenance Error Information Management System (MEIMS) tool used to capture human error in Naval Aviation maintenance mishaps. Built upon the Human Factors Analysis and Classification System-Maintenance Extension taxonomy, the tool provides the framework for examining maintenance errors that lead to mishaps, incidents, and personal injuries. The tool is developed for safety personnel, mishap investigators, Aircraft Mishap Board members, and analysts. In limited usability testing, the tool was found to be useful, but in need of revisions, specifically regarding functionality and user friendliness. Additionally, a tutorial is provided to better prepare targeted users of the tool. The study requires a review of mishap information systems, human error theories related to aviation mishaps, design considerations for human-computer interfaces and usability study applications. A follow-on usability study, conducted using two groups of potential users, one which received the tutorial and one which did not. It includes a survey regarding subjective responses about the prototype tool. The results indicate that the tutorial is effective in preparing and assisting potential users, and that the tool could make a significant impact in the reduction of mishap rates due to maintenance error.