Fatigue Crack In Muffler Support Bracket - P2008TC

[Jack C.]

N344 Failure Pic 28-10-4568-1 Rev A00 dtd 1....pdf (129.93 KB)

Performed a pre-flight check on my Tecnam (N344X, 2019 P2008TC S/N 130, approximately  280 hrs w/ my last annual in May 2021) this week, and found a concerning break on the Muffler Extension Bracket that attaches to the Lower Motor Mount (Port Side).  The Bracket had cracked/broken within  0.2" of the Lower Motor Mount nut/washer, apparently as a result of cyclic loading and fatigue cracking.  The bracket's Part Number is 28-10-4568-1 Rev A00, and it was manufactured on 07/22/2016. Unfortunately, I did not take any pictures prior to removal of the bracket.

As a result there was no support to the Muffler Exhaust Extension tubing.  Note that the crack was not visible in prior pre-flight checks. The attached PDF shows picture of the Bracket; note that there is also gouging on the lower end of the bracket;  all hardware was tight, and it's unclear to me why there is so much flexing to create these conditions. 

I contacted Tecnam (Sebring), and luckily they had the part in stock (about $30), and hopefully I will have it delivered shortly.

Given that the crack is hard to see, I will add it to my checklist, and use a mirror for future pre-flights.

Jack 

[Flocker]

Interesting. My 912iS does not have this part on it.

[buzz]

Hi Jack thanks for posting this. This is good info for the rest of us when we do our prefights. I checked my pictures and yes, I have this piece (P2008, 914, S/N 103). I know I might be missing a bit of perspective with your photo and mine, but it sure seems like mine has a more significant twist in it than what yours looks like. My questions is could you tell if there had been any torsional stress? By this I mean that the way yours looks if it was installed on my plane, it looks like it would require more of a twist in it. Just wondering if you could tell if it was under continuous torsional stress?

[Jack C.]

Thanks for the picture; it appears that your bracket makes a full 90 deg twist vs. the bracket I removed that makes at most a 45 deg twist. Once I receive the new part, I'll take pictures, and verify the twist, as well as attempting to quantify the torsional stresses when installed. When I look at the failed bracket picture I posted, excessive torsional stresses would probably explain the gouging on the lower end of the bracket.

[Mike B]

Jan 22, 2022 3:15:42 GMT buzz said:

<button disabled="" class="c-attachment-insert--linked o-btn--sm">Attachment Deleted</button>
Hi Jack thanks for posting this. This is good info for the rest of us when we do our prefights. I checked my pictures and yes, I have this piece (P2008, 914, S/N 103). I know I might be missing a bit of perspective with your photo and mine, but it sure seems like mine has a more significant twist in it than what yours looks like. My questions is could you tell if there had been any torsional stress? By this I mean that the way yours looks if it was installed on my plane, it looks like it would require more of a twist in it. Just wondering if you could tell if it was under continuous torsional stress?

Buzz...Looks like you have an exhaust extension.  I'm considering one, could you describe yours?  Based on Jack's crack do you have a concern of additional
torsional load?

m

[buzz]

Jan 22, 2022 20:23:49 GMT Mike B said:

Jan 22, 2022 3:15:42 GMT buzz said:

<button disabled="" class="c-attachment-insert--linked o-btn--sm">Attachment Deleted</button>
Hi Jack thanks for posting this. This is good info for the rest of us when we do our prefights. I checked my pictures and yes, I have this piece (P2008, 914, S/N 103). I know I might be missing a bit of perspective with your photo and mine, but it sure seems like mine has a more significant twist in it than what yours looks like. My questions is could you tell if there had been any torsional stress? By this I mean that the way yours looks if it was installed on my plane, it looks like it would require more of a twist in it. Just wondering if you could tell if it was under continuous torsional stress?

Buzz...Looks like you have an exhaust extension.  I'm considering one, could you describe yours?  Based on Jack's crack do you have a concern of additional
torsional load?

m

Negative on extension. If you want to see an extension talk to cole505. He has a nice-looking extension. As far as the concern about cracking I am not worried right now. I was just wondering if Jacks issue was due to that bracket not being twisted enough when it was formed and possibly having been forced into place during construction therefore being under constant torsional stress. Just a thought based on the pictures nothing definite. 

[Jack C.]

Jan 22, 2022 14:40:28 GMT Jack C. said:

Thanks for the picture; it appears that your bracket makes a full 90 deg twist vs. the bracket I removed that makes at most a 45 deg twist. Once I receive the new part, I'll take pictures, and verify the twist, as well as attempting to quantify the torsional stresses when installed. When I look at the failed bracket picture I posted, excessive torsional stresses would probably explain the gouging on the lower end of the bracket.

I installed the replacement bracket last night and twisted it through out its length to a full 90 deg twist.  Also added a couple of washers inside the lower bracket mounting ears such that the bracket could not move or twist (i.e, to prevent gouging on the lower end of the bracket). I'll keep an eye on the bracket over the next few flights.  Thanks for the comments.