This talk describes how performance aspects of a big Air Traffic Flow Management mission critical application are tracked from development to operations. Tracking performance is needed when new functionality is added, to balance the additional services versus the resource increase needed. Measuring and tracking performance is also critical to ensure a new release can cope with the current or expected load. We will discuss various aspects such as which tools and techniques are used for performance tracking and measurements, what are the traps and pitfalls encountered for these activities. The application in question is using Ada, but most of the items discussed are not particularly Ada related.