Ground feathering on PA 34

[scanavos]

After landing on a PA 34, on low RPM taxiing, one engine stopped and feathered. I restarted, it unfeathered rotating above 1000 and on low RPM (800) it gradually stopped and feathered again.
I restarted, it unfeathered and I pulled mixture lever cut off. The engine stopped and after some seconds I saw the dead propeller feathers to rotate slowly to the feathered position.
What is going on?

[stevef]

Prop dome air charge being too high is the first thing I'd suspect. Other less likely causes may be internal oil leaks or broken latches.
Has it just come off maintenance?

[Bonanza_Driver]

Maybe something to do with the low rpm feathering stops (forgot what exactly they were called :\) maybe they're broken as stevef suggested...

But if it the dome air pressure was too high how come it didn't show during the runup when the proper idling of the engines was checked..? :confused:

[Wing Root]

Your case sounds a little unusual since it's moving to feather when stopped. Usually happens due to the very low oil pressure at idle. Most often presents itself with a high OAT and/or an engine which is reaching the end of its life as all the oil leaks past the worn bearings. I suggest keeping RPM at or above around 1000 rpm and usually if you shut down from this it won't feather. Most annoying thing is trying to start the feathered engine and you'll find that a full rich start usually won't work.

[Centaurus]

What is going on?. Presumably you have written up the defect in the maintenance sheet for that aircraft. It should not be flown until the defect is rectified as it may be symptomatic of a more serious fault.

[Big Pistons Forever]

If the prop feathers with the engine not running then feather latches inside the dome have to be broken. These latches prevent the blades from moving to feather when the engine oil pressure decreases as the engine shuts down. This failure is not that unusual on light twins used for training. The repair requires removal of the prop and sending it to a prop shop. You can expect a bill of around $2000 USD.