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In addition to designing fighter engines for stall-free idle to maximum power operation and stall recoverability, it is important to give proper emphasis to sub-idle operation for successful starting. This permits the pilot to confidently bring the engine on-line following an inadvertent flameout caused by either the airplane departing the flight envelope or by a fuel interrupt due to a malfunction. Thus reliable and fast airstart capability enhances flight safety especially of single engine airplanes. Flight testing, therefore, is substantially devoted to airstart evaluation. The paper first explains the influence of engine design features on airstarting, particularly the advantages of the low bypass ratio cycle F100-PW-229 (PW229) engine, which is an increased thrust derivative (IPE) of the highly successful F100-PW-220 engine. Enhancing airstarting capability of the PW229 using variable geometry features and digital control flexibility is discussed.

In recent years, the design and development of military propulsion systems have greatly benefited from advancements in analytical modeling and prediction tools. However, flight testing continues to play an integral role in the maturation of fighter engines. The severity of the fighter mission role dictates the need for capabilities beyond those normally attributed to commercial propulsion systems. While comprehensive static and simulated in-flight engine testing are key elements in developing these capabilities, flight testing provides the avenue for verification that all engine and control functions operate as intended in an integrated environment and that the propulsion system meets with customer, and specifically, pilot approval. In addition to the role that flight testing plays in introducing new propulsion technology into operational service, an equally critical function is served by providing the opportunity for component improvement verification.