I agree with previous comments about what the overall Engineering Change order is the flow of it and how it is beneficial. Since these comments mostly covered the essentials, I would to alternatively add to the discussion the side effects that engineering change orders may add. The process is crucial they can cause a major delay to the project and very costly. I found this link very useful to the overall understanding and managing process of ECOs.

https://sites.insead.edu/facultyresearch/research/doc.cfm?did=46595