A very good question was sent to me, about how the starting system engages and disengages for a large turbine engine, like for an airliner.
We have in the shop all the pieces of an old airliner jet engine, so lets get them all together and see if we can visualize how they work.
This is not how every engine starter drive works, but it's how many of them do.
Note: This is not a sprag clutch. There is a good page on Wiki about the sprag clutch. https://en.wikipedia.org/wiki/Sprag_clutch
The page references one of my videos (!)
A sprag is always in sliding contact when allowing movement. The ratchet clutch described here has no contact at all when the engine is running.
