Doug Buford with the Aft Engine shop removes a heat shield on one of Columbia's engines.

Doug Buford, with the Aft Engine shop, removes a heat shield on one of Columbia's engines. After small cracks were discovered on the LH2 Main Propulsion System (MPS) flow liners in two other orbiters, program managers decided to move forward with inspections on Columbia before clearing it for flight on STS-107. After removal of the heat shields, the three main engines will be removed. Inspections of the flow liners will follow. The July 19 launch of Columbia on STS-107 has been delayed a few weeks