Why: If you can't spell clearly spell-out the requirements for availability, reliability, and maintainability the contractors cannot make these issues features of the design. Thus it is important to be specific in the features the design must manifest. Explanations such as: "You know what I want and what I need, just do it quickly" are self defeating expressions of vague generalities that lead to inferior designs and constant arguments. Be specific about requirements for building reliability block diagrams, using quality function deployment, performing failure mode and effects analysis, conducting fault tree analysis and finally conducting design reviews for reliability.
When: Write the specifications before procurement begins. Plant to spend time with your own Purchasing Department to explain the details and sell the team on the financial advantages for including reliability requirements into the specifications; and likewise, spend time selling your vendors on the requirements and why they are stated.
Where: These are up front decisions to avoid replication of previous problems that are built into previous designs and never corrected.
These definitions are written by H. Paul Barringer and are also posted on his web site at www.barringer1.com