Engine reliability (pistons and turboprops)

Yes; even 5300 has to be BS because it would mean a huge number of engine failures e.g. within the flight training business. In the US there are schools doing 2000hrs a year. Even the PA28-161 in which I did my FAA IR in Arizona was doing 700hrs/year.

I am confused. If an average failure rate of one per 3,200 flight hours would be true and I take the official number of 25,212,000 flight hours for 2019 in the US according to FAA/FSANA, this would convert into over 20 engine out each day. Doesn’t feel right.

MichaLSA wrote:

this would convert into over 20 engine out

It’s not “engine outs per 3,200 flight hours”. It isn’t explained what failure really is.

Also, the “source” at FAA states that most of the failures do not end in injuries or fatalities.

Maybe we can end up with a working statistic here in the end…

MichaLSA wrote:

this would convert into over 20 engine out each day. Doesn’t feel right.

It’s not right. Last time I checked (years ago), I came to a number 60k h or something for piston engines, and a turbine being 5-10 times better. That’s 1/2 to 1 order of magnitude Which is a lot, but not insanely much. One major reason for failure of piston engines is under usage. They simply aren’t run enough on average to achieve optimal reliability. On the contrary, they fail due to corrosion and similar things. Turbines on the other hand, are used mostly commercially. They run a lot, and get proper maintenance always.

So even the 60k vs 300-600k numbers are not an apple to apple comparison.

One major reason for failure of piston engines is under usage. They simply aren’t run enough on average to achieve optimal reliability. On the contrary, they fail due to corrosion and similar things.

I think they often wear out early (in terms of operating hours) due to corrosion related mechanisms acting on cam and rings but do not so often fail as a result of corrosion, pitting induced fatigue failures etc. Occasionally, yes, for example valve spring and magneto impulse coupling spring failures. But I think the more common piston engine failure modes are wear or fuel system related.

I wrote this earlier in the thread from ATSB

For example this:

https://www.atsb.gov.au/sites/default/files/media/29980/b20070191.pdf

The UK AAIB, in the course of its investigation of the Cessna 404 Titan G-ILGW
accident (UK AAIB report 2/2001), raised the issue of engine reliability with
several regulatory agencies and asked for data on in-flight shut-downs by different
models of reciprocating engines. The response from the FAA, and other agencies,
was that no reliable data exist for this kind of comparison, largely due to ‘gross
under-reporting’ of in-flight shutdown of general aviation piston engines. The FAA
assessed the rate as ‘between 1 per 1,000 and 1 per 10,000 flight hours. This failure
rate, qualitatively described as ‘probable’ or ‘reasonably probable’, is well in excess
of the ‘improbable’ or ‘extremely remote’ reliability goals expressed in design
standards.

Ok wow, nice discussion. So statistics are not available or show numbers between 1 per 1,000 and 1 per 100,000 flight hours. That is quite a range. 1 per 100,000 would be turbine reliability.

I think the problems are

• sparse data tends to show clusters, which makes analysis hard
• due to the robust nature of the old engines, a lot of issues are picked up before the engine “blows up” → unreported failures (if you had ECUs, oxygen sensors, etc, this would be different)
• engine failures on twins are mostly unreported (but are thought to be more likely than on singles)
• type of operation needs to be considered (a lot of private ops run the engine on condition, to say 3k hrs)
• different engines are obviously different re failure types: Lyco/Conti (and those two actually have partly different problems), Rotax, and turboprops
• some failures leave no evidence e.g. fuel servo icing, misc fuel system icing, carb ice

In terms of the data, also how well filtered out are engine stoppages caused by, say, selecting a fuel tank with an excessive quantity of air?

AFAIKT the BRS installations in Cessnas aren’t popular as you not only lose payload (not a huge issue in a 182), but also most of the baggage compartment.

We have two Cirri in the club and the argument for them was and is ‘I have a young family’.

While I don’t fly them (didn’t see any reason to spend about 4 AMUs to fly a SR20 and now fly mainly MEPs), I cannot fathom why anyone would be opposed to the chute. It can and indeed often is a lifesaver.