The chairman of the Columbia Accident Investigation Board said today he has no plans to require NASA to recertify shuttle systems before flights resume or to mount a test flight of some sort to validate recommended design changes or to collect more data.

But Harold Gehman said recertification is being assessed as a potentially useful long-range project in light of NASA's stated goal of flying its remaining three orbiters for another 15 years or more.

"The board is considering but has not yet ruled on whether or not a recertification or a requalification of either part or all of the STS system should be necessary for another 20 years of flight," he said during the board's final Houston news conference.

"My own personal opinion is that would not be a return to flight issue. The recertification or requalification issue is related to the announced intention of NASA to fly these things for another 20 years. It's not our charter to address that issue, but we may comment upon it."

Asked if the board might recommend a shuttle test flight before resumption of space station assembly missions, Gehman said "it's a matter under consideration." But after the news conference, when asked to clarify his thoughts on the need for a test flight, the retired admiral said he did not think the board would make any such recommendation.

The board hopes to have its final report finished before the end of July, when Congress adjourns for its summer recess. But that is strictly a target and "we'd rather get it right than get it in a hurry," Gehman said. While the board is still developing and refining its conclusions, Gehman gave reporters a hint of what to expect when the printing presses finally start rolling.

"I can tell you it is going to be a very, very thick report and that it will be in narrative form, that is, it's going to start off 'once upon a time,' you know, at the beginning and it's going to be a multi-layered report," he said.

"That is, you'll be able to have a beginning where it has a very high level cursory discussion of something and then you just keep going and it gets down to the next layer and you keep going and it gets down to a very, very detailed engineering layer. And I also know you're going to kind of have to read the report to pull the recommendations out. It's not going to be a comic book kind of a report."

To the relief of reporters ultimately faced with the challenge of digesting the report on deadline, Gehman said later a list of all the panel's recommendations will be available in an appendix. He said three professional writers have been hired to combine and edit reports from individual board members to give the final document a consistent "layered narrative" style.

"We're going to try and make it easy to read in the sense that each chapter will be kind of a stand-alone chapter," he said. "You're not going to have to be flipping back and forth to appendixes and things like that to find things. Whatever charts and graphs and pictures we refer to will be right there in the text. But it'll be a thick report. It'll be voluminous."

And it won't necessarily blame Columbia's destruction on the impact of foam debris on the ship's left wing 82 seconds after liftoff. While the foam clearly hit the left wing's leading edge at or near where investigators believe a breach occurred during re-entry, it might not be possible to prove a direct connection.

"We may or may not be able to state with unequivocal, complete certainty that the foam strike, which obviously did happen, knocked a hole in the leading edge of the orbiter," Gehman said. "There's no question the foam hit the orbiter, but we may not be able to prove it actually caused some kind of a breach or not. Therefore, because we're working so hard on determining exactly what caused this shuttle not to return safely to Earth and (because) we're looking at so many engineering and physical and mechanical processes, chemical processes, that took place, it has caused us to look broader, much more broadly at the material condition and the operation of the shuttle program."

He said the final report will probe NASA's shuttle operation "probably more broadly than any review in the past. This probably is a blessing in disguise, particularly if you're thinking about operating the shuttle for another 20 years."

"Therefore our findings and our recommendations are going to be based on this very, very broad review and not based on a single, solitary initiating event like the foam hitting the orbiter," he said. "We're not going to rule it out, I mean the foam hitting the orbiter may have caused a breach and that may have been what allowed the heat to get into the wing. But since we can't prove that, and we can't disprove, for example, orbital debris or micrometeorite (impacts), we're left with the position of having the report stand on its own weight.

"And all of these other things that we're looking into, like safety and management and risk assessment and work force issues and the stature of the (safety and mission assurance) organization, all these other things are going to have to stand on their own. Our conclusions and findings will have to stand on the merits of our work and we cannot refer back to the foam hitting the orbiter as proof of everything.

While the board may end up concluding the foam strike was the most likely initiating event, "we can't prove it," Gehman said. "We have to allow for the possibility that something else initiated this event and our report will have to take that into account."

One reporter, using a murder mystery analogy, said enough circumstantial evidence was available for most people to indict the foam. But Gehman disagreed.

"We do indeed have witnesses that saw someone shoot a gun," he said. "But the problem is we don't have a hole. We have a patient who died but we don't know why he died. There's where the analogy breaks down. ... If I had a picture of a hole or if we came back and somebody found a piece of RCC (reinforced carbon carbon) on the ground some place that had a (hole in it), I might change my mind. But as you well know, in this area where we're projecting the breach occurred, we have no RCC. It's all burned away."

Management issues will be a major focus of the final report and the perception that agency managers somehow lost sight of the post-Challenger emphasis on proving it's safe to launch a shuttle rather than proving it's not.

"A considerable part of our report is going to be addressing this underlying and hard-to-pin-down attitude or climate," Gehman said. "Some people have characterized it as a change in posture from one in which you had to prove that it was safe to fly to one in which you had to prove it was unsafe to fly," Gehman said. "In other words, the people who had doubts about anything were essentially outside the circle and had to work their way in rather than the doubters being inside the circle.

"Of course, there are a lot of reasons for this, this is not criminal activity or anything. You have 112 successful flights, you've got to assume you're doing something right. You've got thousands and thousands of dedicated people being very careful about what they do, catching many, many flaws before you launch. So they've got lots and lots of successes to prove they're doing a lot of things right. But there are a number of underlying issues we're going to attempt to address in this report. And we want to be sure that we've got them addressed in a responsible way."

Along those lines, the board will look into what other outside panels determined about the foam threat in years past because "NASA is being reviewed by somebody all the time. Well, what do all these other panels say about this? ... We are actually conducting a review of the literature to see where all these other wise people were on the subject of foam and whether or not if we had been called in before the space shuttle Columbia took off, whether or not we would have raised alarm bells about this foam business ourselves.

"In hindsight, it's really easy to find these flaws," Gehman said. "So if these flaws are out there laying around and everybody should have seen them, OK, well tell me what the next one is if you're so smart. Tell me the next one. If we as a board can't answer that question, we are very slow to sling spears at other people who also failed to answer that question."

But he said "if there's a flaw in the system or a better way to do that, we are going to document that and be very straight-forward in pointing that out."

The CAIB is in the process of wrapping up its operations in Houston before relocating in Washington. Gehman said the board's "hot lines" for public comments and suggestions will be taken down at the end of the month. Since Feb. 1, the board has received 3,150 unsolicited public comments, half of them "what I would call serious inputs," Gehman said.

"A goodly number of them were just letters which said 'I know where a piece of debris is' or something like that. But about half of them were serious analytical suggestions."

He said 778 of the 3,150 unsolicited comments and observations were actually checked out by board investigators.

"About 25 percent of the inputs we got were serious, were valuable, were things we actually followed up on to see if they were actually right or not," he said. "I consider that to be a pretty successful enterprise."