Fwd Carry Through Spar FAILURE

[Les Edge]

The initial inspection was carried out to investigate Inspection Report
Cessna 170-B
Serial # 20908
C-FEER

C-170B, C-FEER, Ser # 20908, TT 2,600 hrs

The initial inspection was carried out to investigate buckled and distorted fuselage skins at the lower strut attach point after an inner tube failure on landing at CYFD July 21, 2012
Further detailed inspection revealed that the forward carry through spar # 0511162-5 had failed inside the LH upper door post assembly # 0513006-44.
It is not possible to inspect the area where the spar failed without removing the wing and spar attach block fitting # 0411129.
The aircraft inspection program on this aircraft has included an intensive corrosion inspection and prevention plan for the past 35 years. At this point corrosion does not appear to be the cause of the failure. It is suspected that the initial crack had been present for some time. The inner surfaces of the carry through spar remain heavily coated with LPS-3 from when they were treated during the last wing removal (1975)
All recommendations of the International Cessna 170 Association for inspection of this area have been carried out during numerous inspections with no discrepancies.
Suggestions include cutting a 3/8 in hole through the fuselage front spar cap plate # 0511000-24 just inboard of the carry through spar attach blocks. This would give a good boroscope view of the inner spar surfaces where it passes through the door post. This aircraft has inspection holes cut in the cabin roof skin over the rear carry through spar ( boroscope inspection is part of the 100 hour inspection for this area) It had always been planned to cut inspection holes for the forward spar but concern over sealing the holes from moisture ingress held this up. An X-ray inspection would discover cracks in this area but suggest costs would be high.
I consider this a very significant failure considering the amount of common 100 series Cessna aircraft around the world.
As the area is opened up further information will be provided.

An SDR (Service Difficulty Report) has been filed with Transport Canada

WhenI figure it out I will include photo and diagram


Les Edge

AME # M095846

[GAHorn]

Thanks for the "heads-up", Les... but I have a question: Of what specific "recommendations of the International Cessna 170 Association for inspection of this area"... are you referring?

As the Parts/MX Advisor of the Assoc'n for the last 12 years I have not participated in production of any specific recommendations other than those which anecdotally call for internal visual inspection, corrosion removal, and anti-corrosion treatments with chromate or poliamide. In several discussions we have encouraged complete disassembly of the carry-through "hat section" for internal visual inspections, and inspection of the attach blocks, which if I understand your comments, would have caught the discrepancies you mention.
In addition, past MX Seminars, specifically the one at Benton Harbor, provided removed spar-cap section from Cessnas which demonstrated buckled/bulged skins at leading edge and fuel tank rivet lines, inboard of the wing-strut. To my knowledge, no written recommendations have been issued over any official approval from this association, although the SRAM did include a section on corrosion which was a reprint of another manufacturer's processes. That was not an official recommendation of this association, however, and was produced outside this association.

Let me or Bruce know if you need assistance posting the pictures. We will be happy to post them for you if you send them to us at headquarters@cessna170.org

Thanks again!

[Les Edge]

Re the inspections mentioned, I at one time read mention of inspecting the bolts and nuts holding the attach blocks for signs of corrossion, It is 35 years since the wings and blocks wewre removed, no problems werer found. Regarding the spar cap and leading edges - no faults were seen here either.

I suspect the the spar was completely fractured and the tire failure imposed side loads which actually seperated the two edges of the fracture apart

Skin has only been lifted in a short section at this point, what is the process for uploading pics ?

Do you know of any other complete fractures such as this.?

[c170b53]

Les, looks like you'll be doing some sheet metal work, good thing you're in the biz. As George mentioned, we've talked corrosion and advised our members to investigate bulges, pillowing and signs of fretting in structural components . Thanks for sharing your discovery, pictures of the damage, pictures of your repair and a write up for our publications would be most welcome.

[Bruce Fenstermacher]

what is the process for uploading pics ?

See instructions here: http://www.cessna170.org/forums/viewtop ... =12&t=8777

It is not that difficult but there are some snags that can get in the way. We are always willing to help folks overcome any hurdles with the forum and would specially like to see these pictures.

[Les Edge]

failed spar still in place with cabin roof partially lifted

These pics show the failed carry through spar. When removed it was obvious that this is NOT a corrossion issue as I first thought. This is fatique cracked and failure over an extended period of time. The pic with the pencil clearly show the smooth edges of the fracture, indication that this has been their for possibly years !!!! This is what bothers me more than anything, I have been licensed aircraft mtce professional for 45 years - my theory has always been that if an aircraft is properly inspected and repaired it can last forever !!!

Prior to removal of the failed spar I cut a .5 in hole in the forward spar cap plate, with this hole it is possible to use a straight boroscope probe and "properly" inspect the inner surfaces of the carry through spar where it passes through the door post.

At this point I would recommend that anyone with a 100 series Cessna ( not unique to the C-170) do this and ensure that interior inspection of the spar is carried out annually. Any fears of moisture ingress are alleviated by the ability to inspect the area. This area is seme ventilated anyway. Liberal amounts of corrossipon inhibitor would be also suggested to be sprayed inside the spar during each inspection. Any A&P or AME should be able to plug and seal the hole.

Transport Canada have the SDR and are discussing with the FAA


Les

[blueldr]

This one sure is a dandy. There must be THOUSANDS of other series 100 airplanes that need an agressive inspection for the same problem. It's hard to believe that this problem could be unique to this airplane.

[c170b53]

Well Blueldr I'm going out on a limb as I'll say this failure is probably unique to this aircraft. That's not to say you'll not find another but it's unlikely you'll find many of them. I seem to remember TC issuing an advisitory to inspect and to physically attempt to move the rivet heads that are adjacent to the fracture illustrated in the photos. It's something I do on annuals, it's for this reason that I did not shrink my wool headliner. It's installed a bit loose which in my opinion looks ok and allows access to have a look see every now and again. TC's concern was the rivets might have sheared but remained in place, likely the FAA is also aware of this problem (rivets) . I'll also go out on a limb and say accidental damage is underestimated as the results take time to manifest themselves.
Thks for the photos Les, that top skin is not that hard to replace, the spar will be a bit harder but its all doable.

[Les Edge]

The aircraft is definely repairable. I agree this could be a one off. But with 30,000 plus of these things winging around, I have a hard time with that. I don't ever remember seeing anything fron Transport Canada regarding rivets in the door post area. Anyhow, as mentioned above, I now have an inspection fix - and every 100 series that I have anything to do with, will have inspection access cut. I have not yet decided which approach to take on the repair. Not concerned with the actual spar replacement ( if I can find a new or NOS one) or the upper skin. The most damage is in the area of the lower strut fitting with wrinckled and buckled skins. This area has not yet been opened up. From a visible inspection, throgh the inspection covers, the gear box, bulkheads and webs do not appear to be damaged.

Fuselage jig : looks like I will be fabricated one. Does anyone have any info ? specs, dimensions etc. ???????????????????????

Fuselage: Find another forward fuselage and splice it in ?????

Find a complete forward door post and bulkhead assy and replace?????

Any and all suggestions accepted. After 40 years with me I don't want to let this one die yet.


Les

[hilltop170]

There sure are a lot of rivits/holes in that spar and the failure appears to go thru several of the holes which is understandable. What were those holes for? Was there an old patch in that area?

When the wings were off my 170 a couple of years ago the spar was carefully inspected and found to be in good shape. There were no holes in my spar like your's has.

[c170b53]

I'll try to find the info; I may have to ask the former editor of the Maintainer our very own Joe Scoles, 170 member and owner. I read his stuff for years and was thrilled to meet him at one of our conventions. Upon meeting him I found out he knows my father in law very well, its a small world. Sorry for the drift but again I know I read it somewhere and basically the inspection is to attempt to move the rivet heads at the top of the door post which attach through 45 degree clips into the carry through spar. Richard those holes which you mention contained the same rivets I'm talking about. In the first photo there appears to be a hole in the centre of the channel at the bottom just before the factory nutplate. Is that a hole? as the crack seems to run right through it.

[hilltop170]

OK, I see what the holes are for now, they are in the gusset that connects the door post to the spar carry-thru. I was looking at it thinking those holes were toward the center of the spar carry-thru. Now I see they are at the outboard end of the carry-thru.

Spar carry-thru

[HA]

can you get a look at the carry through (at least the bottom and backside) by pulling down the speaker/overhead light cover and using a borescope inside the headliner? or the underside by coming in through the wingroot - I'd have to go look at my plane to see if there's access for that with the wings on? That crack should have been visible from the outside since it was all the way through.

[c170b53]

Sorry gentlemen I could not locate the maintenance tip I previously thought I had read and I'm thinking after searching last night that I have way too much stuff.

[bagarre]

Based on the location of the fracture, you wont see this even with the headliner pulled down.
The end of the carry thru spar is boxed in on all sides. You'd need a borescope and inspect from the inside of the spar.

What is the history of the plane? Any unusual treatment or damage that may have over stressed this part?

Considering this and other concerns for corrosion in the carry thru spars, Should I cut a 1/2" hole in my top skin and inspect mine? She's been kept outside for most all of her life.

My annual is in October so this could be added to the todo list.