Enhanced Turbine Rotor Material Design Program A major, multi-year program managed by the FAA Airworthiness Assurance R&D Branch features the development of a probabilistic code to improve the structural integrity of failure critical turbine rotor disks used in commercial aircraft engines. The effort includes a cooperative grant to Southwest Research Institute (SwRI) in conjunction with engine manufacturers General Electric, Pratt & Whitney, AlliedSignal, and Allison. The research team led by SwRI produced a major interim deliverable in the summer of 1997. The first functional version of the code called DARWIN (Design Assessment of Rotors with Inspection) was completed incorporating sophisticated risk assessment methods into design procedures. A successful evaluation and verification was completed by AlliedSignal using a company impeller design example. In its final form, the code will be the basis for an FAA standard that engine manufacturers can incorporate into their design systems. The anticipated outcome when fully implemented will have the potential to reduce the uncontained rotor disk failure rate while providing more realistic inspection schedules. Current design procedures for critical engine parts use a safe-life approach. This method assumes that any material or manufacturing condition that could affect the life expectancy of a part, such as a material flaw, is addressed by the rigorous standard testing procedures carried out in manufacturers' laboratories as well as by conservative estimates of mechanical properties. However, service experience has shown that material and manufacturing flaws that can reduce structural integrity may remain undetected. As an example, the loss of a DC-10 at Sioux City, Iowa in 1989, caused by an uncontained disk failure, was eventually traced to just such an undetected defect. To address this issue, the FAA working closely with the engine industry through the Rotor Integrity Subcommittee of the Aerospace Industries Association identified supplemental design and lifing methods that formed the basis for this research program. The probabilistic design code standard developed by this program will not replace the current safe-life methods but will provide an additional tool to minimize the risk of failure. For further information contact Bruce Fenton, AAR-432, (609) 485-5158.