Online Community of Zenith Builders and Flyers
A Horizontal Stabilizer - Mandatory Inspection has been added (Jan 17) to Zenith Company website; Builder Resources, applicable to all models. Will study, pertinent to my project. Thought others, would be interested.
(Sorry JohnA, entry also in Cruzer forum - do as you may, but a worthy notice, possibly otherwise missed), JohnH
Since mine is a homebuilt and not manufactured by AMD, any issued AD would not "technically" apply to my ship. Of course the verbiage for me would be an SAIB, but I think differentiating the two is nothing more than mental masturbation.
I think the bigger picture (In my small mind, that is) is this;
The information regarding the problem and inspection is now out there on the web in addition to the Zenith website. If my ship and the accident ship have enough parts commonality, I think there is an obligation to perform the inspection. It may be a pain in the ass to disassemble the tail to look at four bolt holes, but as inspections go, its not that onerous.
Look at it from the viewpoint of someone who is not a 601 owner/operator;
if you wanted to buy a 601 and you knew this Canadian directive came out, wouldn't the first three questions be;
1) How much are you asking for the plane?
2) Did you perform the 6ZU spar mods?
3) Did you comply with the Canadian inspection directive?
The other interesting point is that the inspection is yearly. If the issue was one of fabrication wouldn't a one-time inspection to confirm proper construction techniques were used suffice? This leads me to believe that they feel fatigue, time in service may exacerbate the problem
Do I HAVE to comply?-no, not at the moment
AM I going to comply?-yes
My humble opinion
Excuse my bluntness ... This was a significant oversight during the original build.
Assuming I visualized the drawings in the MA(?) properly, this area would be difficult if not impossible to inspect after closing up the stabilizer's front/wrap around skin.
Not sure what the legal requirement of any of this is in the US. Maybe someone can clarify (??).
Thinking out loud ... Taking the stabilizer off the plane and the associated parts with it doesn't come without potential risk as well. Seems that maybe a visual inspection using a bore scope or similar of the stabilizer's front attachments would be a safer first step before requiring a blanket removal/inspection. Especially if you are confident that the HT attachments to the tail didn't contain any gaps, etc. On the flip side, if there is any chance the plane has exposed to high winds directly or indirectly, I can definitely see the justification for full inspection.
I agree and think you've summarized the issue pretty well. This advisory is not about a design defect - it is about poorly fabricated and installed parts. Personally, I paid particular attention to this area when I built my STOL 750 and shimmed any bracket per Caleb's (the then-engineer at Zenith) instructions to eliminate any gaps. The attachment bolt holes were drilled slightly undersized and then reamed for a precision fit. I also had multiple inspections by an A&P and an A&P IA during my build.
Of course, this is not an AD and AD's aren't issued on EAB's in the US, so IMHO there is no legal requirement for any of us in the US, but it should be a wake-up call for all of us to ensure we follow accepted and best practices in assembling our aircraft. This inspection might be a good idea if one did not personally construct their aircraft and especially if they have found evidence of sloppy construction elsewhere!
Unless there is new or different information to persuade me otherwise, I'm not removing my HT for inspection and agree there is a potential for doing more harm than good by breaking down the assembly. I check for HT security before every flight and annually inspect the attachment brackets under magnification with a borescope. I sleep well at night, too! ;>)
I'm rather surprised there hasn't been more discussion on this topic since 2017. I searched all of the forums and didn't find anything more recent so hopefully that means everyone has done their inspections and didn't find any problems. My plane was built by AMD and I didn't see any evidence of movement at the bolts. In fact, it looked like the horizontal stabilizer had not been removed to perform the inspection by the previous owner because the paint was still there on the bolts. My A&P and I removed it and found some issues (see photos):
We found a gap between the trailing edge of the front left bracket and the fuselage, rivets that were not seated fully, elongated bolt holes, and a groove cut in the skin of the elevator by the fairing that is too close, We haven't even cut the holes to inspect the rivets attaching the brackets to the horizontal stabilizer yet! I agree with Matt Heinz when he says to remove the 4 bolts and inspect, no matter how good it looks.
My view on this is the "advisory" was probably sent out because of what happened with the B mod. Zenith was looking to be proactive. I bought my plane and according to the log book it had over 300 hours before the B mod was installed which makes me suspect that the failures that led to the B mod may have had more to do with construction technique(as was apparently the case with the horizontal stab failure) than design defect. In any case, when I brought this advisory to the attention of my previous A&P he said that it looked like about 10 hours of work. As others have stated, I would think you are going to cause more wear and tear removing the stab every year to inspect it. When I bought the plane the previous owner(who was not the builder) showed me how to pre-flight it and this included rocking the stab to make sure it wasn't loose and checking all the mounting bolts. You have to believe the guy in Canada was not doing this. I'm satisfied with checking the stab before each flight.
I agree about not removing the stab every year, especially since it involves drilling out some rivets. But I hope everyone who didn't build their own plane is removing it at least once to check the workmanship. I probably will still remove the 4 bolts every year and do the rest with a borescope.