What pjvr99 has described is a stalled or stagnated start , Bog Down , occurs most often in the T56 when pwr demanded is greater than power available , such a selecteing reverse at high speeds with a high OAT , the RPM will decay outside normal limits and the engine will wind down , if the power lever is advanced to reduce blade angle RPM should recover .I have a LM brochure produced for a C130 operators conference and they use the term "Unscheduled rundown" to describe "bog down".