Derivative Engines Versus New Engines: What Determines the Choice?

A choice between a derivative engine or a new engine for either an existing aircraft or a new aircraft is becoming an increasingly frequent one. Although some factors which govern such a choice are necessarily subjective, there are several objective factors which should be considered. Using summaries of recent or current cases as examples, an examination of the many dimensions of capability, cost, and risk identifies twelve of these objective factors, many of which are often not subjected to rational analysis.