NASA managers say an engineer's email discussing a worst-case scenario based on the assumption a foam debris impact during the shuttle Columbia's launch did, in fact, seriously damage the ship's heat-shield tiles is an example of normal "what-ifing" and not an expression of real concern that somehow failed to reach upper management.

In an occasionally heated teleconference with reporters late Wednesday, Milt Heflin, chief of NASA's flight director corps, and Leroy Cain, the flight director on duty during Columbia's descent, insisted the emails in question were simply examples of the kind of routine engineering dialogue that goes on all the time in the flight control community.

"I would not expect those kinds of things to get elevated to me or for me to then take something like that and elevate it to the management team unless there was something that came out of those discussions that resulted in a recommended change to our procedures or mission rules or something that we were going to do different in realtime related to it," Cain said.

"And the answer to those questions from the MMACS (mechanical systems) folks was, no."

It is worth remembering that if the shuttle's thermal protection system was, in fact, seriously compromised at launch - i.e., the root cause of the disaster was the impact of external tank foam insulation on Columbia's left wing - post-launch discussions about the possible severity of the damage were moot.

If that scenario is what actually happened, there was nothing management could have done to prevent a re-entry catastrophe. The crew had no way to repair or even inspect the underside of the wing and there was no way to alter the ship's re-entry profile to significantly reduce the heating and aerodynamic stress the orbiter would experience returning to Earth.

But the way NASA's management system operates is certainly of interest in any post-disaster investigation and reporters have focused in recent days on how safety concerns at the engineering level filter up to NASA management.

As is now well known, a large section of foam insulation broke away from Columbia's external tank about 81 seconds after launch Jan. 16. In long-range tracking camera footage, the foam can be seen disappearing under the shuttle's left wing and then emerging in a shower of fine particles. The foam clearly hit the underside of the wing, but the precise area of impact is not known.

In the days following launch, engineers carried out an analysis to determine what the foam impact might have done to the shuttle's protective heat-shield tiles.

The relative air velocity between the shuttle and the tank at the time the debris came off was about 750 feet per second, or just over 500 mph. The debris hit the tile at a shallow angle and engineers were concerned it could have broken through the black surface layer across a broad area, eroding and reducing the thickness of numerous tiles.

Three different reports apparently were generated, but only two have been seen by reporters. In those, the effects of a single lost or seriously damaged tile were evaluated. "Contingent on multiple tile loss thermal analysis showing no violation of M/OD criteria, safe return indicated even with significant tile damage," one report concluded.

But the analysis of the effects of a multiple tile loss scenario have not yet surfaced. All that is known at present is that on Jan. 28, a status report was forwarded to mission management that concluded:

"The impact analysis indicates the potential for a large damage area to the tile. Damage to the RCC (reinforced carbon carbon leading edge insulation) should be limited to coating only and have no mission impact.

"Additionally, thermal analyses were performed for different locations and damage conditions. The damage conditions included one tile missing down to the densified layer of the tile and multiple tiles missing over an area of about 7 in by 30 in. These thermal analyses indicate possible localized structural damage but no burn-through, and no safety of flight issue."

That report was issued on Jan. 28. Shortly thereafter, mechanical systems engineers at the Johnson Space Center contacted support personnel at NASA's Langley Research Center and asked for an assessment of what might happen if the left-side main landing gear doors were breached during entry.

Even though a formal analysis concluded the debris impact was not a safety of flight issue, the engineers apparently wanted to discuss scenarios in which the debris damaged a landing gear door enough to allow significant heating in the wheel well.

An engineer at Langley emailed back that "before I begin, I would offer that I am admittedly erring way on the side of absolute worst-case scenarios and I don't really believe things are as bad as what I'm getting ready to make them out. But I certainly believe that to not be ready for a gut-wrenching decision after seeing instrumentation in the wheel well not be there after entry is irresponsible. One of my personal theories is that you should seriously consider the possibility of the gear not deploying at all if there is a substantial breach of the wheel well."

If damage in the wheel well was severe enough, he continued, "something could get screwed up enough to prevent deployment and then you are in a world of hurt." He then went through a list of possible landing issues, all focused on problems with the main landing gear at touchdown.

An engineer at the Johnson Space Center in Houston emailed back: "Your input is beneficial. Like everyone, we hope that the debris impact analysis is correct and all this discussion is mute (sic)."

The status of the left main landing gear wheel well has been the subject of much concern throughout the accident investigation because numerous sensors in the well either failed in Columbia's final moments or recorded higher-than-normal temperatures.

In NASA's latest telemetry timeline (revision 12.1), at least one sensor recorded landing gear deployment at 8:59:06 a.m., a full 26 seconds before contact with Columbia was lost. Reliable sources close to the investigation said today the telemetry is believed to be the result of a sensor failure, or "bit flip," and not any indication of an actual deployment.

Deployment of a main landing gear at a velocity of 12,500 mph would generate significant turbulence and additional telemetry. But other sensors in the landing gear deployment system did not show any change prior to loss of signal.

In a teleconference today, a NASA spokesman said telemetry from the shuttle Columbia indicating the deployment of its left main landing gear 26 seconds before the orbiter broke up was the result of a bad data and not because the gear actually deployed.

Had that occurred, NASA spokesman James Hartsfield said, the crew would have felt a noticeable increase in turbulence and other sensors would have confirmed the event as well. As it is, those other sensors, showing the landing gear firmly stowed, remained unchanged through vehicle breakup.

The left landing gear wheel well has been the subject of intense scrutiny because of sensor data during Columbia's final eight minutes that showed an unusual increase in temperature. Up until this point, investigators had not ruled out radiative heating as a possible explanation. They now believe a jet of hot plasma must have gotten into the wing from a breach somewhere else.

"The temperature trends that were seen by the various instrumentation inside the left wheel well ... was unlikely to have been caused by radiational heating alone, radiational heating meaning that it would unlikely be caused by the aluminum skin of the wheel well getting hot and warming the inside of the wheel well," Hartsfield said today. "That kind of radiational heating alone would not have caused the temperature trend.

"You would likely have to have a breach of skin somewhere and have plasma flow inside the orbiter skin somewhere in order to cause that temperature trend. Now, they do not and have not ... pinpointed any general location as to where that plasma flow would have to originate. The wheel well is not a pressurized area, it's not sealed off by walls completely from the rest of the inside of the fuselage, it has venting in it and that kind of thing.

"So, you have a breach in the skin, which is in the leading edge of the wing or the fuselage or the skin of the wing or the wheel well door seals, any of those could be potential causes for the temperature trends we saw."

During a news conference last week, shuttle program manager Ronald Dittemore said the landing gear doors must have remained intact because the temperature rise - a 30- to 40-degree rise over five minutes - would have been much greater if plasma was flowing directly into the wheel well.

During Wednesday's teleconference, Heflin and Cain went to great lengths to convince reporters NASA's management and problem reporting system worked as designed, even though senior managers were never informed about the Langley landing gear scenarios.

"I was aware of these 'what-ifing' discussions," Heflin said. "I think it was Monday the 3rd. What's interesting is that it didn't surprise me, I didn't think of it as something 'oh my goodness' because I'm used that kind of stuff going on all the time that we don't necessarily hear about unless they believe it's something they need to bring to the flight director and the flight control team to deal with."

Asked if the matter received enough attention, Heflin said "if it comes to the flight director, it's a different story. It did not because they had concluded they didn't need to bring it to the flight director because they believed, with the analysis that was done, and they decided there wasn't anything they needed to do."

He said "the process is a good one. Again, we don't know what happened here yet. When we know what happens, then there'll be other questions we'll be asking ourselves."

But not all the reporters were convinced. One jumped in a few moments later and asked: "Sorry, who said 'there is no reason to rethink the process,' who was that?"

"That was Milt Heflin," replied NASA spokesman James Hartsfield.

"Now, now read that back to me what you just said," Heflin interjected.

"'There is no reason to rethink the process,'" the reporter replied.

"Well now, be careful," Heflin responded with some emotion. "At this point, the process that we used and that we went through is a good process. I stand by that. What I'm saying, at this point, you don't want to rethink the process because you do not know what happened to you yet. We may have to rethink the process later, I don't know, we'll find out. Did you get it this time?"

"I heard you both times."

The teleconference ended in confusion after a reporter repeatedly asked why no one at NASA made a connection about the possibility of serious damage to the landing gear doors based on the original tile impact analysis and the subsequent concerns from Langley.

But the landing gear discussion was prompted by the original impact analysis and it's not clear what the reporter was implying. For their part, Cain and Heflin never seemed to understand the thrust of the reporter's question and the teleconference ended on a sour note.

Earlier in the briefing, however, Heflin said subsequent discussion of the landing gear issue was a routine example of engineers working through "what if" scenarios following an analysis like the one that concluded the foam impact was not a safety-of-flight issue.

"That was the conclusion," he said. "A lot of people were involved in that discussion. Yes, (the engineer at Langley) is an expert, but there are experts in other places, too. This was dealt with by a lot of very smart people reaching the conclusion it was not a safety-of-flight issue.

"And again, let's be careful here, let's don't start taking this and assuming we know what happened here, because we don't yet. But in their particular discussion of the foam and potential contact and damage or whatever, it was concluded it was not a safety-of-flight issue. I'm repeating myself, but again, we train our flight controllers to even go beyond that at times and just continually think of what, maybe, did we miss anything, is there anything we need to be concerned about?

"And in their discussions after that time, they came to the conclusion that what we've got on the books as far as flight rules and procedures and so forth are good, there's nothing else to do and so therefore they did not bring this to the flight director or beyond. They did not, because they did not feel the need to do that. They had reached a conclusion."

Post-launch analysis and debate aside, Cain provided the first glimpse into what the flight control team was thinking as the first signs of trouble appeared during Columbia's descent. Upon hearing a flight controller inform him that four temperature sensors had dropped off line in the left wing, Cain immediately thought of the debris impact.

"I was intimately aware of the debris on ascent and the subsequent analysis and the disposition of all that through our normal process during the mission," Cain said. "I was very aware of that as was everyone else. And when the MMACS (mechanical systems officer) in realtime during entry called me and told me he had these four measurements on the left wing, that's the first thing that entered my mind. But it was momentary."

Maintaining a strictly business approach, Cain and the entry flight control team simply worked through their normal procedures as the descent continued. But as more telemetry failures were noticed and Houston lost contact with Columbia, it began to sink in that something was terribly wrong.

"At one point, I and other people in the room, obviously, knew that we were in a very dire situation," Cain said. "But rather than dwell on that, our training kicked in and we immediately went into action and did the things that we needed (to do).

"Backing up from that, there were several minutes of time after we lost the signal and before we had any kind of confirmation the vehicle had broken up where we marched through our normal procedures for trying to regain communications. We went through and did the things we would normally do as a team. I was not convinced it was anything more than a short-duration loss of comm, which is not uncommon for entry. We were coming up on the time period where I was expecting us to have a short outage, because we changed satellite antenna selections. We didn't expect it to be that long.

"I had brief moments in that timeframe of concern," Cain said. "But like I said, we didn't dwell on those moments. In the training, you go on and do the next step, whatever it might be, what time it is on the clock and how close I am to where touchdown is and whether or not I should have C-band tracking and where the UHF site is. And so we went through our normal procedures because we, in fact, didn't have the information to verify the vehicle was no longer with us. We did eventually, and we activated contingency procedures."

Cain said it was not until he went home late that night that the full impact sank in.

"This was a crew I was particularly close to and it was a crew that was very easy to fall in love with in my opinion," he said. "And that was my experience. We were very close, our children go to school together, it's a very intimate situation. But we are professionals and the Columbia crew, I believe they would be proud of our behavior in the last several days."