This first edition of the guidance material covers how aircraft operational data can be used for decision making and monitoring of aircraft reliability. In order to achieve the highest level of dispatch reliability at lowest cost, it is essential to use aircraft operational data and pilot reports to assess the effectiveness of not only the maintenance program but also the training program. Reliability programs are therefore essential to ensure the high levels of success in achieving safety and dependability expected in commercial aviation. They are also crucial for airline operations to remain efficient in order to reduce cost. With new generation aircraft technology, it is possible to attain data streams that contain valuable quantified information on the health and performance of engines and systems as well as failures or deterioration detected by on-board continuous monitoring. This manual helps operational staff understand how to better organize this data, analyze it and finally report the findings. It also allows guidance on using methods that detect and highlight negative performance and reliability trends and identify the root causes. This process can further help identify the appropriate corrective actions that can be developed to restore performance and reliability to expected levels thus improving safety, efficiency and operational integrity.