A study, which is based on the official FBI documents issued on 11/09/2001, show how UAL and the FAA were tracing two different flights, but both were identified as "UA 93".

The study contains also analysis of documents issued by FBI, LAU, NTSB and 9/11 Commission published after 9/11.

This document can be viewed and/or downloaded here

http://www.scribd.com/doc/27408068/Case-Study-Acars-Ual-Ua93-Rev-3-0b-En