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
according to National Commission on Terrorist Attacks Upon the United States (2004). "Chapter 1", 9/11 Commission:
a Boeing 757-222 on a morning route from Newark International Airport (now known as Newark Liberty International Airport) in Newark, New Jersey, near New York City, to San Francisco International Airport near San Francisco, California (EWR-SFO). It had 182 seats but was carrying only 37 passengers (including the four hijackers) and seven crew members: two pilots, the captain Jason M. Dahl and his first officer, LeRoy Homer Jr.; and five flight attendants. Because one passenger had booked two seats, some early accounts said there were 38 passengers on board. The four hijackers were seated in first class.
Ten passengers and two crew members were able to make calls that went through, providing information to family, friends, and others on the ground
(normally planes with such few passenger would not even take off...)
Granite stones are somber but deeply symbolic
By Kim Vo -- Mercury News -- 8dec07