Had the same problem in one of our 402's, normal operation, but after shutdown it would self-feather in about 15 minutes. Happened only in very cold weather, and it was a sticking locking pin. For what it is worth.
Hung
Well, I wasn't surprised, but our maintenance guys called and said that the prop shop didn't find any particular problems with our propeller. Just as I suspected.
Interestingly, they did decide to replace the spring that goes around the locking pins. I am almost 100% convinced this whole problem is related to those pins, so I hope that by replacing the spring that we won't see this again.
We'll get the prop reinstalled later next week and be up and running again, monitoring for any problems. We'll keep our fingers crossed.
Completely different engine, but similar problem - Aero Commander 500Bs, with Lycoming IO-540 and a Hartzell prop (rather than a McCauley prop) would, according to my Director of Mainenance, feather at idle (<1000 RPM), or after shutdown.
To cut a long story short, it turned out the N2 charge in the prop hub was too high. It was within the manufacturer's settings, however, during certain atmospheric conditions the prop would feather. We got permission from Hartzell to lower the N2 pressure, to prevent this from happening.
So the final word, at least so far, is that Hartzell has decided to reduce the nitrogen pressure in the prop dome, as NoPax was hinting at above. Good call!
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