Runaway Prop Adventure

[Rob]

Had an attention getting experience today. Climbing out some 20 minutes after takeoff the left engine prop on my Commander started running away. RPM surging up and down by over 800 RPM with no warning. This event was not preceded by any power change or other pilot action. Prop control had absolutely no effect on RPM during this episode. This went on for about 90 seconds. Was about to shut down the engine when everything settled down just as suddenly as it started. Now I am left trying to figure out what happened. Logically this has something to do with the governor (overhauled about 350 hours ago), but I want to understand the root cause of this kind of event. Run away propellers is something you hear about but it’s not something you want to experience. Has anyone here had a similar experience? Any ideas on the cause of a problem like this are much appreciated!

[appleseed]

what is your airplane, engine, and prop?

[appleseed]

I see that you recently posted about getting back into 500A. So IO520/470 with phc compact hartzell?

N2 charge in the hub? Oil pressure anomalies?

If it happens again, try to video your engine gauges.

[Rob]

I see that you recently posted about getting back into 500A. So IO520/470 with phc compact hartzell?

Engine is IO-520E & prop is Hartzell EHC-G3YF-2UF. This whole event took me completely off-guard and the only gauge I remember looking at was the tachometer, do things the tach is not supposed to do. If this happens again I will (try) observing oil pressure and some of the other gauges too. I’m going to be changing oil and carefully inspecting the oil filter.

[appleseed]

Take the removable tip of the spinners off and check the N2 charge. There should be a placard in there showing what the charge should be.

5 or 10 psi off won’t cause problems. If it’s more than that, or you accidentally bleed it off while checking, you’ll need an N2 bottle with fitting and regulator etc.

[appleseed]

There might be something in here that will help you:

https://www.avweb.com/ownership/propeller-governor-diagnostics/

Everybody knows Murthy’s 2nd law (if it ain’t broke don’t fix it)

When troubleshooting it helps to remember the corollary: if it is broke, what was the last thing you fixed?

[Rob]

There might be something in here that will help you:

https://www.avweb.com/ownership/propeller-governor-diagnostics/

Very informative and useful article... thank you mr. appleseed! Had a return flight to home base today and was watching all of the gauges carefully. No recurrence of the prop surge/hunting event. Noticed oil pressure was right at upper red line. Not sure if this is the 60 year old gauge or symptomatic of a problem. Changing engine oil tomorrow and will be cutting filter to see what's there.