177 – An Out-of-Control Propeller!

Airplane Owner Maintenance - By Dean Showalter

He departed KSHD yesterday in his super-nice P35 Bonanza, headed for his home airport in Pennsylvania. The ground runup was normal, and things were looking good as he approached his cruising altitude of 7000 feet.

But as he leveled off, Aram discovered he could not control his propeller / engine RPM… it was overspeeding regardless of the position of the prop control. There was only one choice… reduce manifold pressure to a point low enough to keep the prop below red line RPM.

So that’s what he did… the trip home was much slower than normal, but the bright side was that he burned a lot less gas

Since I had just completed Aram’s annual inspection at Classic Aviation LLC, and since Aram is my good friend, I was especially interested in him having a safe flight home, so I was watching his progress on FlightAware. When I noticed he was diverting to Pottstown, PA instead of his home airport, I wondered what was up.

Pottstown is where Dave Pasquale runs an excellent maintenance shop, and Dave is one of Aram’s most trusted A&P/IA’s. I could only assume there must have been some mechanical issue for Aram to divert there, instead of his home airport.

Sure enough, after Aram landed, I received a text… “We have a problem. Prop not governing at cruise.” He had to reduce manifold pressure to 16″ to keep it below red line.

The weird thing was that after landing at Pottstown, Dave got in the airplane and did a ground run with Aram, and everything was normal… but apparently when the airplane is flying, the prop is out of control. We were perplexed.

Bummer! I was so hopeful the new PCU5000 prop governor Aram had us install, was going to solve the developing issue he was having just prior to the annual inspection. The governor manufacturer had even made a special adjustment for the correct pressure necessary for the Beech 278 propeller. Unfortunately, there was something else going on. (By the way, I’m very impressed with the PCU5000 prop governor… scroll to the bottom to see a photo after installation on Aram’s IO-470 engine.)

Now it was time for some research, phone calls, and troubleshooting.

Aram and Dave Pasquale got work on that, and I tried to do my part as well.

There’s a prop shop in California that is known for working on these Beech 278 props, but California is a LONG way from Virginia! Surely it would cost a small fortune to ship a prop across the country and back.

Another option was H&H Propeller Services in Burlington, North Carolina… Yoo Crisp is one of the guys in that shop, and he is also familiar with the Beech 278 props. He was super helpful. I spoke with Yoo, and discovered one option was to perform an IRAN (Inspect and Repair As Necessary) on Aram’s propeller. But before doing that, Yoo suggested I talk with Richard Diamond in the engine shop there at Burlington (Triad Aviation.)

Richard was also super-helpful. He helped me understand a test that can be done to check the transfer collar at the front of the engine. Sometimes, there is oil leakage at the transfer collar which can cause issues with the prop governing system. For all you engine geeks out there, here’s how this test works:

• Run the engine and get it hot, as you would for a cylinder compression test.
• Remove the prop governor as quickly as possible.
• Install a special test pad in that location.
• Perform a leak down test on the transfer collar.
• If it fails this test, the crankcase must be split open to fix it.
• If it passes this test, there is likely something else causing the problem.

A second possibility Richard discussed with me was the plug inside the crankshaft. He knew of another situation where the plug near the forward end of the crankshaft got loose and caused similar problems with prop governing function.

This was also good information.

At that point we had some options to consider, and for Aram’s P35 Bonanza, it seemed that Richard thought the following would be a reasonable order to check things:

1. Test the engine transfer collar with the special test pad.
2. If the transfer collar test passes, remove the prop and check to see if the plug inside the crankshaft may be loose.
3. If the plug is tight, remove the prop and send it for IRAN.

So that’s where we are today in this real life scenario.

If you have any other thoughts that might be helpful, by all means send me an email or leave a voice message here on the website… any helpful advice would be appreciated. Email: dean{at}airplaneownermaintenance{dot}com

I’ll give an update in the podcast after we get this whole thing solved… until then, it’ll have to remain a mystery!

Now, as promised, here’s a photo of that amazing new prop governor:

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