Bonanza Cruise RPM below 2300 N/A?

[zazaboeing]

Hi all!

I've seen somewhere an AD I just can't find right now, prohibiting cruise's RPM lower than 2300 RPM for the IO-520, is anyone aware of that?

Best regards,

[AKar]

There appear to be no AD about this, but Continental has published CSB09-11A [pdf] that "strongly recommends" that engine cruise RPM settings should be no lower than 2300 RPM.

I am not sure if this has led into anything, but it appeared Continental was considering that the dynamic crankshaft counterweights might work out of tune if the engine is operated outside of what would be considered 'expected' power settings.

-Esa

[zazaboeing]

There appear to be no AD about this, but Continental has published CSB09-11A [pdf] that "strongly recommends" that engine cruise RPM settings should be no lower than 2300 RPM.

I am not sure if this has led into anything, but it appeared Continental was considering that the dynamic crankshaft counterweights might work out of tune if the engine is operated outside of what would be considered 'expected' power settings.

-Esa

That's the document I was refering to, thanks for finding it Esa. It's a Critical Service Bulletin indeed, and if I'm not mistaken, it appears to be in effect still.
So, no RPMs lower than 2300RPM in cruise here.

Regards,

[AKar]

It's a Critical Service Bulletin indeed, and if I'm not mistaken, it appears to be in effect still.

It is in effect, yes. Curiously, many of the affected operator's manuals have not been revised since by Continental to include this recommendation. It is not like they are in hurry, the revision A of the CSB dates back to 2014.

This highlights the issue of not-so-obvious variables which may or may not come into play when operating the engines much outside their designed speed-torque values. I am not overly concerned about this one, but it is something to keep in mind, in particular as they don't specifically mention what they mean by "high time" engines. In overall, by the time of the publication of this service bulletin, they really did not seem to understand the issue they had in their hands. Might be interesting to check it out what, if anything, has come out of this.

-Esa

[zazaboeing]

Might be interesting to check it out what, if anything, has come out of this.

-Esa

Yep, I'm also interested if this turns out to be contributing factors to those engine failures.

Best regards

[AKar]

I really can't find anything about this by some google searching, except a few internet discussions that claim, basically, that behind this CSB were engine failures of a single operator flying Cessna 402s (twin TSIO-520, not sure what the mentioned IO-520s were installed on), with "...extremely high-cycle ops, very short flights, worst-case leaning procedures." I find no indications whatsoever that abnormal wear was noticed in any significant number of other airplanes operated with cruise settings below 2300 RPM.

-Esa