"The project has done an excellent job of managing its budget reserves, and this ability to efficiently address problems as they come up has enabled Webb to remain on schedule for its 2018 launch."
"The proximity of all the elements and major subsystem schedules to the critical path means that a delay on any of the elements or major subsystems may reduce the overall project schedule reserve further, which could put the overall project schedule at risk. As a result, the project has less flexibility to choose which issues to mitigate. While the project has been able to reorganize work when necessary to mitigate schedule slips thus far, with further progression into subsequent integration and testing periods, flexibility will be diminished because work during integration and testing tends to be more serial, as the initiation of work is often dependent on the successful and timely completion of the prior work. This is particularly the case with JWST given its complexity."