ESDU 81009 presents a method for estimating the internal drag and airflow of turbo-jet and turbo-fan engines in windmilling and, to a lesser extent, "locked-rotor" conditions for use in the assessment of aircraft performance with one or more engines inoperative. The data can be used for any flight conditions although those of greatest interest are likely to be during take-off, climb, and landing. They can, of course, also be used for cruise conditions, for example, ferry flights or "drift-down" with one or more engines inoperative. No intake or other "installation" effects have been considered. Data on "spillage" drag are in ESDU 84004. Examples show how the data presented in ESDU 81009 may be combined with intake spillage-drag data to give an estimate of the total drag increment arising from an inoperative engine. Information relating to the empirical development of the methods using a one-dimensional flow theory as a basis is given in an Appendix.