Simply... Reliability Engineering is... well... not very simple. That is because of:

1. The very disciplined Design Of Experiments it takes to devise tests for the known failure modes during expected and anticipated uses and environments without imposing situations that will never be seen in actual use,
2. The rather complicated testing equipment and technical experience needed to measure functionality under various combinations of stresses,
3. The statistical nature of the methodologies, measurements and analysis needed to predict, with an acceptable confidence level, lifetime information of a product.

Even in light of Reliability Engineering's complexity, the input to PD is the establishment of specific product functions and goals that can be designed, technically implemented and validated. So the drill down needs to outline, for us Techies, specific product functions, goals of functionality and acceptable probabilities of the actions that must be met.

As we did for Quality, an illustration of how the various disciplines of Reliability contribute to the PD effort is shown below. Generally, a project manager provides a Product Requirements Specification (PRS) describing the features and functions of the product. Marketing provides a Marketing Requirement Document (MRD) describing product, market and consumer strategy. Quality (QA and QC) provides Quality guidelines. In this case Reliability Engineering (RE) provides the crank to reduce all of the above to distinct product functions (f). Here, each f is a concise description of the performance of a product function, which can be designed and technically implemented. It also describes the desired statistical goal of the function over time and under acceptable circumstances with acceptable failure levels, which can be measured or assessed. Note that any function is composed of from one to multiple qualities, f (q1, q2... qn).