Experimental engine update requirements

[mhubel]

I have a Zenith CH601XL with a Jabiru 3300 engine. Jabiru has posted a bulletin requiring the replacement of all through bolt nuts with ones that don't meet common aviation standards (threads extending past the nut) and then locking the nuts in such a way that the torque can not be double checked. There is some issue not to be addressed here that this is solving a possible non problem and in the process having a significant probability of doing harm.
This update does not have the word mandatory in the title it as a Lycoming "AD" level document might but the intent is there.
The question is, as an experimental aircraft with an engine which has been modified in other ways anyway, it is still a legal obligation to perform all manufacturer specified updates?

[steveinindy]

it is still a legal obligation to perform all manufacturer specified updates?

I am not 100% certain but my theory has always been that just because you don't have to doesn't mean that you probably should purposefully avoid doing so. They issue these sorts of things for a reason. Better safe than sorry....

[mhubel]

In this case the situation is that there is strong reason to believe that doing the update can do more harm than doing nothing. It requires replacing nuts with ones which extend past the end of the bolts (no threads exposed) and the use of a very aggressive thread lock compound. This requires that the torque be set very quickly and there is only one shot at setting the torque, ever. Further, it has been demonstrated that even if torqued to spec, it is possible to "warp" the cylinders. This can only be determined after everything is back together and the thread lock has set. Too late to fix it.

Additionally, this fix addresses situations which include poor engine maintenance, poor fuel selection and unusually high load operations (glider towing?). I believe this is very likely to on the average cause more harm than good unless every update is done by the "factory" which is not practical and I am not sure they can even get the cylinder warp problem right every time.

Bottom line is that being truly safe may be best achieved by doing nothing.

To date, I have updated the POH restricting maximum power and would like to make this the permanent update.

The other choice of course is to use the engine as an anchor and get a different engine. This is a serious consideration.

[teknosmurf]

Bottom line is that being truly safe may be best achieved by doing nothing.

That is quite a defiant comment...

As an engineering manager I cringe at these kinds of mentalities. I know nothing about your engine or the details behind it, but what basis are you using to justify your comments? Do you believe someone who is not qualified came up with this recommendation? Why do you believe the people, who presumably know the situation the best (since it's their engine and they have LOTS more insight than anyone else), would recommend something that would cause damage (remember, their reputation and liability is the one on the line here)?

You did not mention if the service bulletin state that limiting power would be an acceptable alternative. If it is, then don't make the change and just placard the aircraft...if they did not say that, I think it would be a silly thing to do.

Bottom line is the company has better things to do with their time than work on correcting a problem that doesn't need fixed. Things like that (especially for things that have already been fielded) are extremely expensive and time consuming...it is better to get these correct the first time. By issuing the bulletin they have effectively admitted to making a mistake and are providing what they believe to be a better solution...not a worse one. Yes, mistakes happen, but when the company is dealing with life-or-death equipment, those mistakes should be assumed to be minimal.

I do not presume to know your background, nor does it really matter. Unless you are a mechanical engineer and have extensively researched both the benefits and shortcomings of the particular change on multiple platforms (not just on your one engine) it would be hard to say your "beliefs" are better than the factories with any amount of certainty.

Lastly, please remember that industry standards are just that...standards. Standards become standards because it is the most widely used and accepted practice and was adopted by some controlling body. This DOES NOT mean the standard is the absolute, correct, biblical thing to do in every circumstance! Standards are provided as a guideline for when no or little overriding data exists. I am pretty positive the answer to your question is no, you do not have to implement the changes, but I think it would be somewhat foolish not to.

This is just my $0.02...take it for all it's worth.

[Dana]

If it's not a certificated engine then there is no legal requirement to comply with the change. But I'd want to know more about the issue the change is intended to correct before deciding to ignore it.

[Dave Prizio]

I think it is pretty clear that you do not have to do the fix Jabiru recommends from a strictly legal standpoint, but I can see no reason why you would not be willing to go along with their recommendation. By failing to take their advice you put yourself in the position of claiming, in effect, to know more about Jabiru engines than Jabiru. If something would go wrong with your engine related to this fix, you would be in the unenviable position of trying to defend that claim.

Your contention that the fix would do more harm than good seems to lack support. It is doubtful that Jabiru would have made such a recommendation if they felt that it was not worth the trouble. They, at the very least, have a strong interest in protecting themselves from future liability, which means that they surely gave this issue some serious thought.

The recommended nuts and installation procedure are not exactly standard airplane practices, but then neither are many other things on the Jabiru engine. This may have come as a shock to you if you were not previously aware of it, but it is not exactly a secret.

I personally find this service bulletin annoying, but I am going to comply with it on my plane. I urge you to consider doing the same on yours.

Dave Prizio
Texas Sport Cub N114DE