I recently shutdown an engine inflight in a C310. The a/c was underperforming after a climb from 8k to 10k. I was only getting 100 - 300 fpm. I checked engine instruments and everything appeared normal. After leveling off, the left Prop started surging between 1800 - 2500 RPM. I tried to adjust the prop several times to get it to stabilize with no luck.

Engine instruments for both engines were in the green. I decided to do a precautionary engine shutdown and ran the Engine Failure During Flight. I declared an emergency and got vectors to a towered field nearby. The right engine was performing normal and the landing was normal. I elected to not restart the engine - even though it was not fire, fod, or friction - as I did not know the cause and was fearful of something getting worse with a potential over speeding prop. No checklist for uncontrollable prop btw. Additionally, the right engine was operating normally and the aircraft was stable and performing. I was very close to a short field and within gliding distance of a towered field.

Mx: The prop governor was inspected by a mx shop and appears normal. The prop screen to the crankshaft was removed and a heavy amount of sludge was found. The belief is the sludge was clogging the screen and not allowing the oil to get to the Prop governor consistently and led to the surging. The prop has approximately 950 hrs and is 27 years old. The plane has been annualled every year for the last 20 years. Last annual was 12 hrs prior to incident with 6 flights performed post annual.

I hope everyone can learn something from this.

Questions:
1) Should the props have been removed and cleaned during annual inspections?
2) The props are within TBO for hours and outside of TBO for calendar time. Any overhaul shop recommendations for IO-470s?
2) Any thoughts on a restart in that situation? The initial post incident flight runup on the ground had everything performing normal. The preflight runup before the incident flight was also all normal. The a/c flew a 3-hr leg the morning of the incident flight with no issues. No issues/abnormalities on the morning preflight runup either.
3) Any other areas you would check before returning the a/c to service?
4) Any reason for the lack of climb performance from 8k - 10k if the prop was not surging at that time?

Special thanks to ATC! You are all awesome. Thank you.

Unless the owner requests it, no one is going to remove props as a matter of course during an annual.

By chance is this a turbo 310?

Normally aspirated

What oil additive(s) are you using and what type and weight of oil is normal for your engine?

another ancillary question: Do you use an Air oil separator?

just diagnosing.

No additives at the time. Normally Camguard.

No Air Oil separator.

20W50

sludge formation ususally comes from a non-ashless dispersant (Detergent) oil.

Camguard is GREAT at loosening old deposits and cleaning out your sump. Its possible, if the plane is "new" to you, that the previous owner wasn't so diligent.

Hot components, Like turbochargers are known to produce coke and other byproducts that like to condense into sludge. A hot running engine produces more.

The prop governor is essentially a high pressure oil pump which takes its supply from your engine and uses it to actuate the hub. Being a HP pump, low flow increases oil temp in the governor. I dont know if its possible to check the temp of an operating prop governor.

any mention of the last time the governors were OH'd?

If there truly was enough sludge circulating in the oil system to restrict flow through the screen in the prop governor gasket, I would be concerned about plugging up an oil transfer tube in the crankshaft which supplies oil to a rod bearing. Every engine creates sludge. Remove the prop from a 1000 hour engine and you’ll likely see 1/8”-1/4” of sludge compacted on the inside wall of the crankshaft. Just like a centrifuge, the rotating parts of the engine cause the heavier particles in the oil to “spin out”. Even smaller components like the drive gears, etc., will have some sludge build up in the hollow, rotating areas. So, sludge is not unusual. Sludge circulating through the oil system IS unusual and can cause serious problems, as you discovered, if it accumulates in the wrong places.

To me, I'd think 27 years, on a prop with a 12yr calendar TBO, is too long. You didn't say whether the props or governors have had other maintenance in the meantime, like a reseal or IRAN.

We see a lot of sludge build up, with Continental engines 800 hours and up. the build up ranges from thick grease to hard cake. We remove props for TKS De-Ice kits, so we see quite a few.

Lycoming has a service letter about periodic cleaning sludge from inside the crank flange.

To me, I'd think 27 years, on a prop with a 12yr calendar TBO, is too long. You didn't say whether the props or governors have had other maintenance in the meantime, like a reseal or IRAN.

That's interesting. Is there a recommendation to pull props and check for sludge on Continentals? Is this a common issue that I am not aware of or the GA community in general?

Is there a time/calendar interval we should all be checking our props for sludge build up if it is not normally checked on annual inspection? Or does following TBO times remove any need to do a sludge check/cleaning before TBO for us part 91ers that may think we can go beyond TBO?

I agree. It was recommended at last annual to do a replacement. The estimate came in around $35k to do both props. I have been doing some research on overhaul vs replacement. This incident speeds up my research and desire to improve the props.

To me, I'd think 27 years, on a prop with a 12yr calendar TBO, is too long. You didn't say whether the props or governors have had other maintenance in the meantime, like a reseal or IRAN.

310 owner. I’m not buying the sludge as the root cause. Good job getting it home safe. I had one grenade on my 310, thankful for the 2nd engine.