Just one minute and 24 seconds after reaching the region of maximum aerodynamic heating off the coast of California, telemetry from the shuttle Columbia shows the first sign of unusual heating in the ship's left wing main landing gear wheel well, according to a dramatic new accident timeline released today by NASA.

The timeline plots Columbia's course from a point 400,000 feet above the Pacific Ocean west of Hawaii to the point over Texas where the last data from the stricken ship was transmitted. Overlayed on the map and the shuttle's ground track are boxes showing all of the unusual telemetry beamed back from the shuttle as it streaked eastward toward destruction.

The new timeline includes the latitude and longitude of the orbiter at each point where telemetry was transmitted, the altitude and velocity of the spacecraft at that time and additional details about what each bit of telemetry actually indicated.

As the chart shows, re-entry began in earnest at 8:44:09 a.m. as the shuttle fell into the discernible atmosphere 395,010 feet above the Pacific Ocean northwest of Hawaii. At 8:50:53 a.m., Columbia began encountering the region of peak heating at an altitude of 243,048 feet and a velocity of 24.1 times the speed of sound.

One minute and 24 seconds later, at 8:52:17 a.m., telemetry indicated the start of an unusual rise in temperature from a sensor on the left main landing gear brake line on the inboard sidewall of the main landing gear wheel well. The shuttle's altitude at that moment was 236,791 feet and its velocity was Mach 23.58. The shuttle was well off the coast of California west of San Francisco at a 38.9 degrees north latitude and 129.2 degrees west longitude.

Twenty-four seconds later, a temperature sensor on a strut in the wheel well that faces the main landing gear door began registering an unusual temperature increase. Starting at 8:52:59 a.m. and continuing for another 12 seconds, four temperature sensors near the back of Columbia's left wing suddenly dropped off line. Wire bundles leading to the sensors were routed along the left, or outboard, side of the main landing gear wheel well before crossing in front of the well and into the shuttle's fuselage.

Moments later, in mission control at the Johnson Space Center in Houston, mechanical systems officer Jeff Kling noticed at least some of the unsettling telemetry.

"FYI, I've just lost four separate temperature transducers on the left side of the vehicle, hydraulic return temperatures," he told entry flight director Leroy Cain. "Two of them on system one and one in each of systems two and three."

Cain: "Four hyd return temps?"

Kling: "To the left outboard and left inboard elevon."

Cain: "OK, is there anything common to them? DSC or MDM or anything? I mean, you're telling me you lost them all at exactly the same time?"

Kling: "No, not exactly. They were within probably four or five seconds of each other."

Cain: "OK, where are those, where is that instrumentation located?

Kling: "All four of them are located in the aft part of the left wing, right in front of the elevons, elevon actuators. And there is no commonality."

Cain: "No commonality."

NASA officials said today the most likely explanation for the temperature rise ultimately seen in the wheel well was hot plasma circulating inside the wing from a breach, or penetration, elsewhere. Such a breach could have damaged the hydraulic sensor wiring, explaining the loss of data from systems at the back of the wing, while at the same time explaining the rising temperatures in the wheel well.

That much is informed speculation. That a breach occurred at some point well before breakup now seems all but certain.

"Preliminary analysis by a NASA working group this week indicates that the temperature indications seen in Columbia's left wheel well during entry would require the presence of plasma (super heated gas surrounding the orbiter during re-entry)," NASA said in a statement.

"Heat transfer through the structure as from a missing tile would not be sufficient to cause the temperature indications seen in the last minutes of flight. Additional analysis is underway, looking at various scenarios in which a breach of some type, allowing plasma into the wheel well area or elsewhere in the wing, could occur."

In any case, the next unusual telemetry was transmitted at 8:53:31 a.m. as Columbia was passing 231,304 feet above Sonoma County, Calif., at 23 times the speed of sound. Another rear elevon hydraulic line temperature sensor failed "off-scale low."

More ominously, at 8:53:46 a.m., as the shuttle passed above Interstate 505 west of Sacramento, Calif., a sensor on the left main gear brake line, mounted on a strut facing the landing gear door, began registering an unusual, steady increase, jumping from 1.4 degrees Fahrenheit per minute to 5.5 degrees per minute. The temperature recorded by brake line temperature sensor A continued increasing until loss of signal.

Twenty-four seconds later, at 8:54:10 a.m., brake line temperature sensor B began showing an unusual increase as Columbia passed above the Toiyabe National Forest. Ten seconds after that, telemetry shows the shuttle's wing flaps, or elevons, began moving in response to the ship's flight control system to counteract increasing aerodynamic drag on the left side of the shuttle.

Just two seconds later, at 8:54:22 a.m., as Columbia neared the border of Nevada, two temperature sensors mounted on the left side of the shuttle's fuselage above the left wing began experiencing an unusual temperature rise. One went from the normal 1-degree per minute increase to 7.6 degrees per minute while the other, located slightly aft, showed a rise to 5.5 degrees per minute.

After two more anomalous temperature readings while Columbia was streaking across Nevada, telemetry indicates increasing aerodynamic drag at 8:55:21 a.m. By this point, the shuttle had fallen to an altitude of 224,002 feet but its velocity was still a blistering 21.9 times the speed of sound.

The end was just five minutes away.

Streaking across Arizona, a flurry of readings painted an ever-worsening picture of problems in the shuttle's left wing. Additional landing gear sensors recorded fast jumps in temperature, a sensor on the underside of the left wing dropped off line followed a few seconds later by a sensor on the upper side of the wing, both presumably due to wiring damage elsewhere.

At 8:56:30 a.m., as Columbia descended through 219,820 feet, the flight control system began the first of four planned "roll reversals," or banks, to bleed off energy, routine maneuvers to help a returning shuttle shed velocity. The first roll reversal was completed at 8:56:55 a.m.

Just northwest of Albuquerque, telemetry registered a "bit flip," or an anomalous reading, at 8:57:19 a.m. from a left hand outboard landing gear tire pressure sensor. Five seconds later, a second left outboard tire pressure sensor exhibited unusual readings.

Additional elevon trim motions were recorded at 8:57:35 a.m. as the shuttle crossed 216,062 feet above Interstate 40 at Mach 20.21. After additional telemetry hits, the data shows the start of "sharp" elevon trim motions around 8:58:03 a.m. The timing is approximate, but the flight control system is obviously struggling to maintain the shuttle in the proper orientation.

At 8:58:32 a.m., left main landing gear tire pressures and temperatures began dropping off line followed 14 seconds later by a decrease in the left inboard wheel temperature. At 8:58:39 a.m., Columbia's backup flight system computer issued an alarm calling the crew's attention to the loss of tire pressure telemetry.

"And, uh, Hou..." shuttle commander Rick Husband radioed. His transmission, however, was cutoff, presumably because the shuttle's antennas did not have a clean line of sight to NASA's communications satellite.

After additional readings from other sensors recording anomalous data, the backup flight system issues a final tire pressure alarm at 8:58:56 a.m. Ten seconds later, telemetry from a "downlock" sensor indicates Columbia's left main landing gear had deployed. A nearby "uplock" sensor, however, showed no change and flight controllers believe the gear remain stowed through loss of signal.

"Flight data including gear position indicators and drag information does not support the scenario of an early deployment of the left gear," NASA said in a statement.

By this point in the timeline, the aerodynamic drag was increasing at a rapid rate because of the deterioration of the left wing.

Kling suddenly tells Cain: "We just lost tire pressure on the left outboard and left inboard, both tires."

"And Columbia, Houston, we see your tire pressure messages and we did not copy your last," astronaut Charles Hobaugh radioes the crew from Houston.

Cain: "Is it instrumentation, MMACS?"

Kling: "Those are also off-scale low."

Husband then makes what turns out to be his final attempt to contact Houston around 8:59:28 a.m.:

"Roger, uh, buh..." Husband began around 8:59:28 a.m. But this last transmission from the shuttle was cut off. Seconds later, at 8:59:30 a.m., two of Columbia's right-firing yaw jets ignite to assist the elevons in keeping the shuttle on course. One second after that, data shows the elevons sweeping through their largest deflections yet. The left elevon moved up 8.11 degrees.

One second after that, all data was lost. At that point, the shuttle was roughly 200,767 feet up and traveling at Mach 18.16 northeast of Abilene, Texas.

Just a minute or so after this loss of signal, time-stamped video shot by the crew of an Apache helicopter showed the tracks of multiple pieces of flaming debris arcing across the Texas sky.

"Columbia out of communications at present with mission control as it continues its course toward Florida," NASA commentator James Hartsfield said at 9:01 a.m. Two minutes later he said, "Fourteen minutes to touchdown for Columbia at the Kennedy Space Center. Flight controllers are continuing to stand by to regain communications with the spacecraft..."

"Columbia, Houston, comm check," Hobaugh radioed at 9:03 a.m. And again seconds later, "Columbia, Houston, UHF comm check."

There was no reply.