We operate the 100/300/400. There is, as SlowAndSilly said, a mod. you can install, that will disengage the YD when the engine autofeathers. After we modified our 100-series, we can take off with YD ON, regardless of flap setting. When performing the autofeather test each morning, we check that the YD is disengaged as the engine autofeathers. But I guess that mod costs money... If my memory serves me right, you can use YD for flap 5 take-offs on the -100 without the mod?