SAE AIR5656

This SAE Aerospace Information Report (AIR) provides a methodology for performing a statistical assessment of gas-turbine-engine stability-margin usage. Consideration is given to vehicle usage, fleet size, and environment to provide insight into the probability of encountering an in-service engine stall event. Current industry practices, such as ARP1420, supplemented by AIR1419, and engine thermodynamic models, are used to determine and quantify the contribution of individual stability threats. The statistical technique adopted by the S-16 committee for performing a statistical stability assessment is the Monte Carlo method (see Applicable References 1 and 2). While other techniques may be suitable, their application is beyond the scope of this document. The intent of the document is to present a methodology and process to construct a statistical-stability-assessment model for use on a specific system and its mission or application. Engine stability analysis and assessment, and the allocation of stability margins, form integral parts of the design and development of every gas turbine engine program. The existing guidelines for stability assessments are documented in ARP1420 and AIR1419, which have been widely utilized throughout industry. However, the existing guidelines do not recognize the statistics of operational demands and can therefore potentially overemphasize low probability events. Applying statistical techniques allow an assessment of the probability of encountering a destabilizing event and thus enable a risk assessment to be made for inlet/engine compatibility. The application of such techniques form the basis of the methodology discussed in this Aerospace Information Report.