Seat Rails; Substitution of "blind rivits" for solid rivits

[thruthefence]

On certain very popular "high wing" single engine aircraft, there is an Airworthiness directive requiring replacement of the crew seat rails, or "tracks" if certain cracks are found. The rails are considered primary structure, and are installed with solid rivets. Many of the rivets are extremely hard to install properly, and the FAA has given some allowance in SAIB no. CE-90-03R2, which allows the use of machine screws. No mention of "blind" rivets.

My problem, is I have presented an aircraft for a pre-purchase evaluation, and discovered a seat rail installed exclusively with blind rivets, I assume to be 'cherrym@x'. Calls to the OEM tech rep advised "that while I can't give a written opinion, such an installation doesn't meet the TC." However he would "talk" to the principals in the sale. The aircraft SRM advises blind rivits "are used where appropriate" ( ?? ). No installation instructions for the specific job exist. The OEM service bulletin ( referenced by the AD note ) gives no help. The anedotal information out there has always cautioned against the use of blind rivets in this case. I talked to an aftermarket manufacturer of PMA'd seat rails, and the engineer's drawings had numerious handwritten notes stating " NO BLIND RIVETS" in the margins, but no regulatory reference.

My question to the group is this: Can someone give me regulatory 'chapter and verse' on this installation? The seller is hesitant to spend money correcting what may not be a problem, and the buyer is hesitant about acquiring a unairworthy aircraft, and possibly having to spend money down the road.

I neglected to mention I can find no record of this rail replacement in the aircraft's records. ( Imagine that! )

Sorry about the long post, and thanks in advance for any advice & guidance.

 

[MintJulep]

I can find no record of this rail replacement in the aircraft's records.

Seems like that is your "out". "The aircraft has undocumented modifications, and it is not possible to determine if the modification has been performed by a licensed A&P or in compliance with any AD or SB." Or some such.

 

[rb1957]

isn't the point of your inspection, to find these things ?

it sounds like the installation is not iaw the AD or other acceptable engineering (RDA, 8110, ...) and must be brought to an acceptable standard to complete the sale.

of course the principals involved could arrange for this paperwork to cover teh installation, instead of reworking the installation, but i would be hesitant to permit this if it isn't acceptable to the OEM's AD (if it was acceptable they would have listed it, the use of blind rivets ilo solids, as an acceptable alternative.)

 

[thruthefence]

rb1957, Perhaps I wasn't clear enough in the original posting,but the AD note (14 CFR 39) which carries the power of law, refers you to an OEM service bulletin, which says to replace the rails when certain cracks are found. It doesn't detail the replacement, so checking the FAA approved SRM, it states " blind rivits are used where appropriate". From the fact that I am quoting from a SRM (structural repair manual) issued by the OEM, can I not extrapolate that the blind rivets CAN be used? The fact that this little airplane even has an SRM amazes me. but again I ask, where is my authority, other then heresay to kill this deal. An existing, undocumented repair, or alteration can be approved after the fact, but like anything else, it requires "approved data". That is what I am seeking.We have two motivated people, a buyer & a seller, both wanting to do the right thing, but also not wanting to spend unnecessary funds. I'm sure the OEM tech rep was doing the best he could, being cautious to put the compamy's stamp on something that could turn into a mess in the legal sense.

 

[rb1957]

IMHO is sounds like a sloppy AD, but then maybe that's typical of the class of plane ?

it sounds as tho' there's no paperwork conforming that installation to anything. i'd say that you're inspecting the plane to find these things and then it's up to you to accept thru SRM provisions or not, then it's up to the principals to arrange coverage or to redo the work iaw the AD.

for you i'd say the key question is would you put your stamp on this installation ?

 

[thruthefence]

Not without regulatory data, the seeking of which is the purpose of my posting here.How would you read " blind rivets are used where appropriate"? How do would you define "appropriate"?

As far as the "sloppyness" of the AD's language, I will leave that to others, but "It is, what it is", and it is, though sloppy, "the law of the land".
here's a link, if you're interested:

http://rgl.faa.gov/Regulatory_and_G...F9645B32611A4A04862569BA004BC930?OpenDocument

Actually, as I stated in my first post, I was hoping for input from someone in the industry who could speak from experience, rather then conjecture. It is not appropriate, in a business setting to simply 'wash one's hands of it' and walk away. Not without something I can point at and say "here is the direction in which we must proceed, in black and white".

 

[jetmaker]

The use of "as appropriate" IMO implies for structures that already use blind rivets in their installation. I would not consider blind rivets appropriate for use in "primary" structure, especially if their installation is undocumented. Only way to allow the use of blind rivets at this location without detailed analysis is by demonstrating similar application of existing blind fasteners.

As a minimum, I would tell buyer/seller that they need to be removed since there is lack of documentation on what was installed and how. Holes may be oversized, elongated, cracked, and the type and quality of the blind rivet is unknown. Since you are having to remove them, I would quote the cost of installing the rails per the manufacture's recomendation using the screws. Check out this link for some installation information:

http://mansfieldlanding.com/forum/b...essna_172_l_model/archive/2006/09/05/188.aspx

As you say this modification is not documented, then one must assume that the rails have not been replaced and inspections are required still in accordance with the AD. Having partaken in several pre-purchase inspections before, a repair like this might be a small percentage of the overall purchase price which the buyer/seller would be able to come to terms with. This ensures the aircraft complies with the AD, and absolves the buyer from having to do further inspections.

jetmaker

 

[rb1957]

i think jetmaker has proposed a solution for you ... the AD presumably isn't signed off, and therefore is still in effect (mind you there are continuing inspections so the AD remains in effect, without terminating action (abit unusual). if the AD is signed off then someone else has taken the responsibility for the mod.

it sounds like you've already talked to the OEM and they have not endorsed this installation; that's worth alot.

you're looking for someone to tell you "black and white" "chapter and verse" the "right" answer. i doubt there are many of them around, and fewer of them on eng-tips.

you're found something that smells, you have to do something about it, and no-one has suggested that you "wash your hands of it". if you thought it was acceptable you'd never have posted your question. so it sounds as though you want to reject it 'cause it doesn't comply. sounds reasonable to me ... make the principals aware of the situation, give them the alternatives that are acceptable to you (presumably redoing the work or getting and approved RDA).

 

[thruthefence]

RB, You are correct,I don't like the look of it. All my experience (and it's all anecdotal in this instance) some 35 years now tells me that it's not "according to Hoyle". And if I was relicensing this aircraft, ie complying with the Annual inspection required under 14 CFR 91 . I would indeed reject it as "not meeting the type certificate", at least until I was proven wrong by regulatory data. However, I am acting as a paid 'consultant' to perform what is commonly known as a 'pre purchase' evaluation. 'Pre purchase' evaluation or inspection, is not defined in the FAR's. It can be whatever the principles agree it is. It is often defined by contract, sometimes by a handshake. All I can do is give my recommendations, backed up by data. If the sale falls through, based on my wrong information, I could be civilly liable. In this litigious environment, this is not a stretch. There are hundreds of thousands of dollars at stake. The aircraft in question has been maintained for many years by well known, I thought well respected shops. Apparently for years no one has taken notice of this seat rail anomaly. Shucks, maybe all that stuff I've heard all those years is wrong? Wouldn't be the first time.

As far as feeling bad about seeking "chapter & verse" and "black & white answers" as opposed to 'opinions', I have alway been taught, (BSME '64) and believed that of all disciplines Engineering is the least subjective. There may be more then one path to a solution, but only one correct answer. Your comments, while not helpful in my current situation are appreciated.
As far as Jetmaker giving me an "out", can you Imagine going to a customer and saying " well, Boss,we gotta install a set of 16 G crew seats & related structural alterations in yer airplane"?

I would be interested in the approval process Jetmaker went through for this alteration. Maybe his fsdo is more malleable then mine.

 

[40818]

thruthefence, your in a bit of a hard spot it seems. But if you take a step back and think that if it were one of your children in that seat, would you be happy with the rivets then?
I would suspect not and that would lead you to the correct answer, as if there were an accident and it came out that your assessment "allowed" the blind rivets i suspect you would be in a whole world of problems. Sometimes its more than just what the law is (which is generally the Minimum requirement), but what your happy with to sign/stamp.

 

[GregLocock]

Surely (stop calling me Shirley) you can perform a calc that suggests whether the aluminium blind rivet will perform adequately in shear/tension compared with the original fastener?

My guess is that you can't possibly give the OK.

While you can design joints to work well with pop rivets they have to be designed that way, in particular no peel, no tension.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rb1957]

ok you're doing a pre-purchase inspection.

tell the prospective owner that the plane needs to have tha AD incorporated and the facts of the case as you see them ... which sounds like ...
1) there is an unknown installation on the seat track installation,
2) the log book does not have the AD signed off
3) you, personally, are uncomfortable with the seat track installation and would recommend either having an enginnering shop/licensed mech prepare an RDA to cover the installation (and to sign-off on the AD) or have someone install the AD fresh (preferred?).

the only person to lose in this scenario is the current owner, the prospective buyer would (should?) be happy with the inspection and negotiate with the seller about this aspect of the inspection.

in my experience, engineering is sometimes less of a definitive science and more of an art ... judgement (opinions) lead facts ... we'll never know everything about something, but we have to know enough to reach a conclusion.

 

[jetmaker]

If you are the "consultant", who are you working for? Buyter or seller?

When I have overseen pre-purchase inspections (as a buyer, not as a mechanic), I hired a mechanic to review the plane logs and do basically a higher level annual inspection. If the mechanic found things that "just didn't sit right", or were incorrect, I would often walk away from the deal as one does not know what other shortcuts have been taken elsewhere. When we are talking about the safety of my passengers and my life, I am funny about making sure that the plane history is well known.

If you are representing the buyer, present your findings, and your recommendations. I would expect my mechanic to present this information about the seat track, and give me feedback on the proper fix (cost, downtime, etc.). What you have done is essentially like a home inspection process. You present the findings, and whether they are per code or not, it is a discrepancy that the buyer ultimately has to agree to or not. This alone would be grounds IMO to walk away from the deal if the seller were not to bring the price down or correct the issue. If the buyer values your opinion, which they should seeing as how they have hired you, then they should consider what you say, and follow you advice.

If you were hired by the seller because this defficiency was found by the buyer's mechanic, then I can see your situation about litigation. However, again getting down to the facts, I do not see any data to support this installation with blind rivets. In fact, I see a good reason for rejecting it...

Following on Greg's comments, although the blind rivets may be structurally acceptable from a static standpoint, they are more than likely deficient in the fatigue aspect. I get the feeling that this area is of higher fatigue concern as the SAIB CE-90-03R2 indicates that the screws are acceptable "provided the holes are ream fit and spotfaced". The ream fit implies a tighter fit is required due to fatigue issues. So again, at a minimum, the hole fit of the blind rivets needs to be confirmed, but as most of us know, blind rivets are not hole filling, and not intended to provide good fit. The consequence of this installation is that the floor pans may eventually crack and need to be replaced because of this defficient (IMO) installation. Talk about expensive. I would have no issues rejecting this installation based on the wording in SAIB CE-90-03R2.

jetmaker

 

[jetmaker]

In a follow-up with my previous posting, I think this situation gets even more complicated than first thought. My concern is this, if the original rivet size was 3/16, and they installed 3/16 blind rivets, there will clearly be a hole-fill issue, and possible fatigue damage to the holes in the floor pan. Thus, a dye penetrant or eddy current check needs to be done at each hole, and I would recommend "zero-timing" each hole to ensure you know what you are working with. Then install the 1/4 screws as suggested.

If the blind rivets were upsized to 1/4 already, then you have a big problem as the above still holds true, and "zero-timing" would be prudent. However, this now means the holes will be bigger than 1/4". Maybe you can get away with a first oversize if luck. But the problem is now you have more area out in your gross section than what the original AD allows, thereby requiring more comprehensive structural analysis of the floor pan structure and possible seat rail. As there are access holes in the floor pan already, it may not take much to show the installation good with the oversized fasteners, but it still needs to be done and adds cost.

jetmaker

 

[thruthefence]

Actually, it has gotten a little simpler. I have found my "out" if you will.

When all else fails, read the instructions.

http://www.peerlessaerospace.com/pub/Productimages/TAF_CHERRYMAX.pdf

page 7, disclaimer at the bottom of the page.

This indicated to me that the use of blind rivets would have to go through the field approval process to be a legal installation. I have no doubt that the unknown person who installed this rail was also aware of this fact, thus the lack of a maintenance entry.

This information was presented to the owner, along with an estimate of removing, inspecting supporting structure, and installing a PMA replacement seat rail at the co-pilots inner position. The rail will be installed with a combination of solid AD rivets, & machine screws.

It remains to be seen if he will discount his price based on this information, pay to have the work done, or simply walk away.

As has been surmised, I haven't "liked the look of this" from the start. But when trying to close a deal, "don't like the look of it" without facts doesn't impress anyone.

thanks again for the input.

PS Jetmaker, I as again, what was the approval process for the installation of the late model seats in the 172? I agree it looks like an excellent AMC.

 

[dgapilot]

Thruthefence,
Before you sign off those seat tracks, you may want to look at Order 8900.1 Volume 4 Chapter 9. The substitution of solid rivets with blind rivets unless specifically authorized by the manufacturer, is a major alteration and requires Engineering approval. There is nothing in the older Cessna manuals that allows substitution of fasteners. The 1996 and after airplanes are covered by a Structural Repair Manual (different type of seat tracks though) and in that manual there is a statement that blind fasteners can be substituted only in places where there is no access to buck solid rivets. Unless you have an 8110-3 that authorizes those blind fasteners you will be returning an unairworthy aircraft to service. Having replaced countless seat rails on Cessnas (150 thru 337), I haven't found any rivets that aren't accessable. Some may be hard to get, but with time and the right bucking bar, all are accessable. I ran a shop doing structural repairs for many years and it was not uncommon to spend as much as an hour to get that one rivet that was hard to get, or go to the lathe or milling machine and make a bar to fit the area you are trying to get.

If you use screws and nuts per the SAIB no. CE-90-03R2, it notes that the seat rails need to be spot faced to provide a surface for the screw head to seat on. If blind rivets were to be approved, I would think that the same spotfacing procedure would be required to have the heads seat properly.

Please keep in mind that if you are signing an inspection on that airplane that you are buying everything on that airplane! If there are unauthorized repairs or alterations, and if there is an accident and those unauthorized repairs contributed to injury or death, you will be liable. Seat tracks are something that I won't give a pass to unless they meet the inspection requirements and are installed properly. AD87-20-03R2 doesn't specificaly call out inspection of the track installation, but you inspection checklist should cover it as appendix D specifies seats and belts for apparent defects.

My biggest objection to this thread is that if there is even a question in your mind, it should be listed as UNAIRWORTHY and the owner/buyer need to determine who will pay for it. I've seen this type of shoddy maintenance come from otherwise reputable shops all the time. It doesn't make it right. As mechanics, it is our job to identify the problems and either repair them properly or sign off the airplane as unairworthy.

Let the customer know that owning an airplane is expensive and he better be prepared financially, or not buy it. Until you have enough mone to buy and fly an airplane equivelant to the best one that your custmers own, don't feel bad about telling them that they need to spend money maintaining the airplane. If the job was done correctly, they wouldn't have to pay for it again.

David Schober

 

[jetmaker]

thruthefence,

You would have to contact the owners of the website. They are the ones who did the work, not even my plane. Found the link and thought it might be of value.

jetmaker

 

[thruthefence]

DGApilot, Thank you for the excellent reference. As of September 13, 2007, the Airworthiness Inspector's Handbook (FAA Order 8300.10), Air Carrier Operations Inspector's Handbook (FAA Order 8400.10) and General Aviation Operations Inspector's Handbook (FAA Order 8700.1). This of course is the information I need, and I should have thought of it myself.
However, please read the my previous postings regarding the scope of this job. It is not an annual inspection. I am not releasing this aircraft as airworthy, ( or un-airworthy, for that matter). I am reviewing the records and general condition of the aircraft for possible purchase. When the subject of the seat rails was pointed out to the seller, he asked me to provide technical data supporting my view. For the last five years, the aircraft has been maintained and inspected, by a large, well regarded Maintenance shop. One of the largest in this part of the country. His first comment was, of course that "if (insert FBO's name here) bought it off, it must be OK." Well I'm sure you have heard that before. The rest of the aircraft seems to be well maintained. The records, with the noted exception seem orderly,with no gaps. The 337's match OK city's list to the letter.The AD note listing & summary is complete and maintained. There is no telling how long this rail has been in the aircraft, but as you said, "this doesn't make it right." As you know, I, nor anyone else certificated under 14 CFR 65 has the authority to "ground" this aircraft. Only the owner/operator or the "Administrator". As I stated before, the "ball is in the seller's court" now. He indicated he will meet with the inspection department of his maintenance provider, & discuss this problem with them. Now, with "chapter & verse", rather the anecdotal "so & so told me 'bout them rivets back in'89", he will be taken seriously. Thanks again to everyone for their input, especially dgapilot.

 

[dgapilot]

Glad to be of help. When I ran a shop, I wouldn't do a "pre-purchase" inspection since there is no set scope and detail. I would have them commit to an annual or have tham give me a written list of items they wanted done. If I did the annual, I would come up with a list of discrepancies and present the costs for those repairs. If the buyer backed out and the seller chose not to have the work done, he would get an unairworthy annual signoff per 43.11. The list of discrepancies would go right in the log book so there was no question of what was still unairworthy.

If the work was done to a specific list provided by the buyer, I would make a 43.9 entry and note again in the log book those items that were still outstanding. This way it covers you down the road.

I was "invited' to testify for the FAA in a certificate action a couple weeks back. When part of my testimony indicated that I had seen the individual in question blatently violate the regulations, the judge asked why I didn't call the FAA. Thinking about that later, we have no requirement to notify the FAA when we see regulations violated, and if we were to call, our business is based on word of mouth, so everyone would find out very fast and our customers would dissapear. Damned if you do and damned if you don't I guess.

 

[thruthefence]

The buyer is one of my corporate customers ( I have a small side business, providing itinerant aircraft maintenance for Cessna Citation & IAI 1124 "westwind" operators hence the "thruthefence" username ) who wants to add a "huntin' & fishin'" aircraft to the fleet. The aircraft in question is a C206. Your comment about 'word-of-mouth' is right on target= our general aviation community is too small to tell the customers " take this junk airplane out of here." Thanks again for you & everyone's comments.