Harold Gehman, chairman of the Columbia Accident Investigation Board, said today two interim recommendations will be released late this week or early next and that the panel likely will write its final report in June. Gehman also said "privileged," or confidential testimony from senior shuttle managers, engineers and technicians, will never be made public, either in a public hearing or in final report transcripts.

"If a witness under privilege tells us that a board meeting was a sham and people weren't free to speak up or something like that, then we will corroborate that, which will see the light of day," Gehman said in a brief interview following a news conference. "But as far as the public hearings are concerned, the public hearings are essentially board meetings in public. That's what we do all day long. We interview, we talk to people like that and it's simply an opportunity for the public to see how we work and go along with us. I mean, you're learning at the same time we're learning. It's not a press event, it's not a news event, it's just an opportunity to do some of our business in public. And that's the intent of it."

The CAIB is interviewing senior shuttle managers and engineers under conditions of confidentiality. By granting such privileged status, the board guarantees witnesses their testimony will never been made public and that criticisms of systems, procedures or other individuals will not be traceable. The idea is to encourage a more open, more honest dialogue with board members and investigators.

Under this policy, the public will never hear directly from Linda Ham, for example, chairman of NASA's mission management team during Columbia's flight, or any other managers responsible for deciding what to do about the foam impact during launch that is now believed to have played a major role in the disaster.

Asked if conducting such interviews in secret might represent a disservice to the public, Gehman said "we consider this to be a strength, not a weakness."

"We are going to be able to get at the intricacies of that process in a way that you could never, the Rogers Commission (that investigated the Challenger disaster) could never, for example, get," Gehman said. "By granting people privilege, we're going to find things out that they wouldn't say in public. And so we believe we'll actually be able to go deep and get a richer and more fundamental understanding of these processes than you can in public.

"Now in order for it to get into our report, we're going to have to corroborate what they say. Just because somebody's mad at his boss or somebody doesn't listen to his opinion, he can say that in privilege. That doesn't mean it's going to make it into our report."

Gehman said the board is finalizing two interim recommendations, one formally asking NASA to routinely obtain in-flight imagery of shuttles to look for signs of damage - already in work by NASA - and the other aimed at implementation of non-destructive evaluation or testing - NDE - to check the health of various systems like the panels making up the leading edge of the shuttle's wing. Gehman said those interim recommendations are undergoing final technical review and could be released as early as Friday.

As for the board's future activities, Gehman said "I think the months of April and May, I suspect we're still going to be receiving data."

"But I suspect in May, the rate of receiving things is going to start to taper off," he said. "We're still interviewing witnesses, still picking up debris, we've got the OEX (data) recorder, which hasn't been analyzed yet. So we're clearly going to be on the receiving end through at least the rest of April.

"I think around May it's going to shift to where we're going to start doing more deliberations and more output-oriented things, issuing more interim recommendations and then start to shrink the staff down. In June, the board's going to have to roll its sleeves up and start writing."

Asked if the final recommendations might include any directives to redesign or strengthen the leading edge systems, Gehman said "I can't give you any sense of that at all." But he said the CAIB is "very concerned about the characterization of an aging vehicle."

One such age-related issue is the health of the carbon composite leading edge panels that protect the shuttle's wings from the fierce heat of re-entry. At present, engineers do little more than visually inspect the panels between flights for signs of damage that might need repair. They do not subject the panels to more sophisticated types of NDE that might reveal hidden problems.

"If NASA doesn't know the condition of its vehicles, we would be leery of recommending that they fly," Gehman said. "Some of these things might be pretty simple, you know, a CAT scan of the leading edge, you can do it in place, you don't have to remove it, if it passes you're good to go. But there are other areas, too.

"I'll tell you one of the things that's really hanging out in my mind is, I find it to be an intellectual weakness to take the O-ring story and the foam story and keep beating NASA over the head with it unless you could point to exhibit C, D and E."

He was referring to the O-ring seal failure that doomed Challenger in 1986 and the foam debris impact to Columbia's left wing during launch that is believed to have led to the wing's failure during re-entry. In both cases, NASA continued to launch shuttles even though engineers knew the systems in question - booster O-ring seals and external tank foam insulation - were not operating properly. But Gehman said two such instances do not necessarily make a trend.

"What are the other three things that are continuously sending you signals? I'd like to find what those other three things are," he said. "I'd like to find some more things that are kind of strange looking, kind of funny looking and NASA says we're going to live with them. ... I find it to be not very intellectually honest to just beat (NASA) about the hindsight thing. I'd like to find other funny looking numbers they've also decided to live with and then be able to make a judgment about that."