For total development cost, which includes the expenses involved in developing a new engine to MQT, plus the cost to correct service related deficiencies and costs for continual performance and reliability improvements over time, the derived equation includes a production quantity term as well as thrust and Mach number. The TOA method links certain engine performance characteristics with time to provide a measure of an engine's state of the art. The refined TOA model is based on 29 U.S. military turbojet and turbofan engines developed and produced during the past 30 years. The model predicts the man-rated MQT date as a function of certain of the engine's performance and design parameters. The parameters include engine thrust to weight ratio, turbine inlet temperature, and specific fuel consumption, which are the three most important technical characteristics in the turbine engine development process.
All parameters needed are readily available at an early stage of planning for a new system.
Care must be exercised in using these models to ensure that inputs are consistent with the data base used in this study. For example, cost estimates will reflect military technology and the manner in which programs were conducted during the 1950s, 1960s, and 1970s. If an engine is developed that is not in the mainstream trend, such as a variable cycle or lift engine, the estimating relationship described may not apply. To the extent that a new program differs from historical conditions, extrapolation will be necessary. These models are provided as educational examples of technology developed and used by cost engineers.