For all those who are inspired by flight, and for the nation where powered flight was first achieved, the year 2003 had long been anticipated as one of celebration - December 17 would mark the centennial of the day the Wright Flyer first took to the air. But 2003 began instead on a note of sudden and profound loss. On February 1, Space Shuttle Columbia was destroyed in a disaster that claimed the lives of all seven of its crew.

While February 1 was an occasion for mourning, the efforts that ensued can be a source of national pride. NASA publicly and forthrightly informed the nation about the accident and all the associated information that became available. The Columbia Accident Investigation Board was established within two hours of the loss of signal from the returning spacecraft in accordance with procedures established by NASA following the Challenger accident 17 years earlier.

The crew members lost that morning were explorers in the finest tradition, and since then, everyone associated with the Board has felt that we were laboring in their legacy. Ours, too, was a journey of discovery: We sought to discover the conditions that produced this tragic outcome and to share those lessons in such a way that this nation's space program will emerge stronger and more sure-footed. If those lessons are truly learned, then Columbia's crew will have made an indelible contribution to the endeavor each one valued so greatly.

After nearly seven months of investigation, the Board has been able to arrive at findings and recommendations aimed at significantly reducing the chances of further accidents. Our aim has been to improve Shuttle safety by multiple means, not just by correcting the specific faults that cost the nation this Orbiter and this crew. With that intent, the Board conducted not only an investigation of what happened to Columbia, but also - to determine the conditions that allowed the accident to occur - a safety evaluation of the entire Space Shuttle Program. Most of the Board's efforts were undertaken in a completely open manner. By necessity, the safety evaluation was conducted partially out of the public view, since it included frank, off-the-record statements by a substantial number of people connected with the Shuttle program.

In order to understand the findings and recommendations in this report, it is important to appreciate the way the Board looked at this accident. It is our view that complex systems almost always fail in complex ways, and we believe it would be wrong to reduce the complexities and weaknesses associated with these systems to some simple explanation. Too often, accident investigations blame a failure only on the last step in a complex process, when a more comprehensive understanding of that process could reveal that earlier steps might be equally or even more culpable. In this Board's opinion, unless the technical, organizational, and cultural recommendations made in this report are implemented, little will have been accomplished to lessen the chance that another accident will follow.

From its inception, the Board has considered itself an independent and public institution, accountable to the American public, the White House, Congress, the astronaut corps and their families, and NASA. With the support of these constituents, the Board resolved to broaden the scope of the accident investigation into a far-reaching examination of NASA's operation of the Shuttle fleet. We have explored the impact of NASA's organizational history and practices on Shuttle safety, as well as the roles of public expectations and national policy-making.

In this process, the Board identified a number of pertinent factors, which we have grouped into three distinct categories: 1) physical failures that led directly to Columbia's destruction; 2) underlying weaknesses, revealed in NASA's organization and history, that can pave the way to catastrophic failure; and 3) "other significant observations" made during the course of the investigation, but which may be unrelated to the accident at hand. Left uncorrected, any of these factors could contribute to future Shuttle losses.

To establish the credibility of its findings and recommendations, the Board grounded its examinations in rigorous scientific and engineering principles. We have consulted with leading authorities not only in mechanical systems, but also in organizational theory and practice. These authorities' areas of expertise included risk management, safety engineering, and a review of "best business practices" employed by other high-risk, but apparently reliable enterprises. Among these are nuclear power plants, petrochemical facilities, nuclear weapons production, nuclear submarine operations, and expendable space launch systems.

NASA is a federal agency like no other. Its mission is unique, and its stunning technological accomplishments, a source of pride and inspiration without equal, represent the best in American skill and courage. At times NASA's efforts have riveted the nation, and it is never far from public view and close scrutiny from many quarters. The loss of Columbia and her crew represents a turning point, calling for a renewed public policy debate and commitment regarding human space exploration. One of our goals has been to set forth the terms for this debate.

Named for a sloop that was the first American vessel to circumnavigate the Earth more than 200 years ago, in 1981 Columbia became the first spacecraft of its type to fly in Earth orbit and successfully completed 27 missions over more than two decades. During the STS-107 mission, Columbia and its crew traveled more than six million miles in 16 days.

The Orbiter's destruction, just 16 minutes before scheduled touchdown, shows that space flight is still far from routine. It involves a substantial element of risk, which must be recognized, but never accepted with resignation. The seven Columbia astronauts believed that the risk was worth the reward. The Board salutes their courage and dedicates this report to their memory.