Engine Hours vs Time

40 h/a is 3.3h/m on short flights. I know of one O200 of great age, but well looked after, which is still reliable on such a regime. I'm dubious about some engines abandoned for most of the year, with much less usage.

I'm also interested in this as I have the opportunity to fly on a 12 year old DA40 STAR, full IFR. Engine has only 800 hours, current owner flies only like 40h/year (VFR only) and seem to have lost interest in his hobby.

He told me the engine will be kept "on condition", meaning that an engine oil sample is taken each year for analysis.

Is there an added risk flying IFR in an aircraft which is "on condition" ?

40hrs/year would be OK for the engine if the flights are well spaced i.e. close to 1 flight per week, lasting 1 hour.

It is possible that the owner was doing a sightseeing trip each weekend and that's it.

But I think it is unlikely. Most likely the engine sat around for months and will be full of corrosion.

Over 12 years, you need to check the logbooks (to the extent that you can trust a logbook written up by the seller) to see the usage pattern. Any gaps of a few months suggest a damaged engine.

Oil analysis alone is good (I do it too, from every oil change) but it is not enough. For example here in the UK we had a 4x fatal crash of a PA28 (G-AVRP - the URL to the AAIB report is truncated by google and the method I used to get the full ones no longer works) where the camshaft was found to have been severely damaged by corrosion, with large chunks having fallen off it. I sent that report to some US engine builders and they said they would expect to see metal in the oil filter but maybe not in oil analysis which looks for very small particles only. Obviously in this case the "maintenance" company never cut open the oil filter.

To most UK owners, "on condition" normally means a compression check only, not anything to do with the oil.

Whether corrosion increases the chance of a sudden failure of an engine is a good question. I do know of one pilot whose engine had nearly seized in flight, and when it was later opened it was found to be full of rust. It had been improperly stored by the aircraft manufacturer and fitted to the airframe when already corroded - on at least dozens of planes they made. But there is no apparent accident pattern as a result.

The financial saving resulting from running past 2000hrs is very very small. For example the engine fund for a £30k overhaul at 2000hrs is £15/hr. A £30k overhaul at 2500hrs is £12/hr so you save just £3/hr, which is negligible. Obviously people do it to avoid paying for an overhaul but if you have no engine fund what will you do when you get to the real end? Scrap the plane?

The IO360 in my Falco is currently in bits due to a prop strike. It only has 150 hours but in over 20 years. I started flying her at 130 hours and did two oil changes in that time, the last one being only one hour before the prop strike, and cut both filters open. When the engine was stripped it was found to be very heavily corroded and I still had the second oil filter on my bench waiting to be cut open so here was a perfect opportunity to inspect an oil filter from an engine with a known corrosion issue. There was only the very slightest evidence of filings in the filter and if I didn't already know the engine's condition I would not have drawn the conclusion that the engine was on its way out. Perhaps the third filter might have revealed more if I had got that far. I did not have analysis done which I'm now regretting as it would have been useful to know the results.

I think you are right... corrosion will not show up in the oil filter until it starts to make items like cam followers break up in a big way. Then you will get shiny bits in the oil filter which pick up with a magnet.

Corrosion ought to show up in oil analysis, but almost nobody does oil analysis. I think less than 10% of the really dedicated owners do it, and on the hire/training fleet it is unheard of.

There is a fair comment: if your oil results go up, are you really going to open up your engine, if the oil filter is OK and the compressions are good? It depends on what you see, I suppose...

Which reminds me.... my stock of prepaid oil analysis kits is going down nicely so I will soon revisit my earlier plan to syndicate the purchase of a good number of these kits. They ought to be under £10 each that way. Postage to America is about £3.

Corrosion related accident on a PA32

BEA Report - PA-32R-300, Saanen

The IO-540 builded in 1976 had only 1256 hours in 2010. Some interesting engine pictures in the report.

That's a very good report.

I see they give the name of the maintenance company. The UK AAIB would never do that - presumably because the company lawyers would make sure...

This is a good bit:

ACTIVE ENGINES:
Engine temperature and length of operating time are very important in controlling rust and corrosion. The desired flight time for air cooled engines is at least one continuous hour at oil temperatures of 165°F to 200°F at intervals not to exceed 30 days, depending on location and storage conditions. This one hour does not include taxi, take-off and landing time.

This
On the camshaft, a wear of approximately 4 mm was found on the cam which actuates the inlet valves of cylinders 5 and 6.
suggests no engine maintenance done at the Annual.

This
A large number of ferrous particles up to 1 mm in size were found in the oil sump.
suggest no opening of the oil filter.

This
When the accessory housing was opened, it was found that the gears for driving the magnetos were incorrectly positioned, i.e. they were offset by one tooth. This offset could limit correct setting of the ignition timing.
suggests the engine never made the rated power, which ought to be evident on the RPM / fuel flow values at takeoff assuming the correct prop is fitted. Not to mention the sub-spec climb performance.

No AD checks:
The fuel injection system of the Precision Airmotive RSA 10ED1 type with P/N 2524273-11 and serial number 67028 did not correspond to the modification status applicable to this type at the time of the accident. No evidence that AD 2009-02-03, RSA-5 or RSA-10 "fuel injector servo plug" had been carried out was found in the technical records.

However, a bit of a silly conclusion:
The FOCA and the competent foreign authorities should consider measures which ensure that recommendations of the manufacturers regarding operating hours and calendar-based due dates are integrated into the maintenance programmes that are approved by the authorities, regardless of whether aircraft are operated commercially or privately.
because a mandatory 12 year life would kill much of private GA, and I don't think can be supported by any engineering evidence.

Peter,

the report is excellent, I agree, the consequences however might be the end of private GA in Switzerland or at least on Swiss register as they will now impose the 12 year limit unless the aeroclub and AOPA Switzerland manage to stop them. However, what I hear this has spread already and some other registrar countries like Germany is looking into the same direction.

Most engines in private planes will have a maximum of 1200 hrs in 12 years, MANY will have maybe half of that. I would have welcomed a check regime whereas after 12 years engines SUSPECTIBLE to problems would have to get boroscoped and checked to be good for some period again (6 years at a time) but to ask owners to tear down perfectly good engines at 600 to 1200 hrs just to cover their behinds will be the end of GA. Nobody can or will afford this, it will mean that the engine fund cost factor will increase from some 20 Euros per hour to up to 70.

My engine is now 2.5 years after rebuild and has about 150 hrs on it... At the going rate I'd have to throw it away at 720 hrs since Overhaul... and no, I can't afford another one.

Responding to the original post, I think it depends strongly on how and where the engine has been stored. An engine stored inside in the desert is unlikely to have corrosion problems for decades, but an engine stored outside in a wet, perhaps salty climate is a completely different story.

That said, the focus on 12 years is a European thing - few owners in the US would know about the Lycoming service bulletin on the subject, or worry about it. Condition as determined by owner and his mechanic is what matters, and if you're flying the aircraft you should be happy too.

One of my engines has had no overhaul logged since it was built in 1971, but I have reason to believe it was overhauled to some level (off the books) in 2000. One previous owner was a technical director for an automobile manufacturer and his hangar was attached to his house... Seems to be a good engine regardless with 900 hrs total time, and its going to be flown for as long as it seems to be a good engine.

PS Timing gear "one tooth off" strikes me as a red herring. Regardless, you can generally check power with a full throttle run up, noting static rpm.