Since a milestone was missed it may have an impact on the entire project team and the various departments involved mainly the R&D. The PM will have to consider the more amount of time that will be needed to identify the problem and fix it by understanding the reason causing the problem and identifying based on this problem how many other tasks will be affected and will have to be altered depending on the new changes required which may also include a change in the design consideration. Apart from this the what other resources will be needed for the change and how much it would cost for these changes to get into practice is what will have to be considered by the PM depending on the budget of the project. However, if there was enough task slack in the Gantt Chart made initially in order to identify the problem and fix it then not much changes would be needed to be made in the gantt chart and only the cost and resources needed would have to be considered.