Officials say the Space Shuttle Columbia's skin could have been somehow pierced, allowing superheated air inside the space craft during its descent through Earth's atmosphere.
The Columbia Accident Investigation Board made the announcement Thursday as investigations continue into the February first disaster when seven crew members died.
Engineers are now considering scenarios in which a breach of the shuttle's skin would allow super-heated air into the wheel well or the wing.
Investigators concluded that a missing tile would not be sufficient to cause unusual heat buildup inside the wheel well before the accident, such as previously thought.
The board also says that the landing gear was not deployed early.
Wednesday, the U-S space agency NASA released an e-mail from a space agency engineer warning of the possibility of "catastrophic" consequences after Columbia's launch. When a piece of foam struck the shuttle, the engineer said heat could penetrate the shuttle's wheel well, causing the tires to explode and blow the doors off the hinges.
Officials say they did not act on the e-mail because they had concluded the broken piece of insulation foam could not have caused extensive damage to the heat-shielding tiles.