Why isn't there an STC replacement for the Cessna 172 seat rails that require an AD?

Posted by andybader@reddit | flying | View on Reddit | 16 comments

Apologies if this is way too specific a question, but I figured I'd try. Many small Cessnas have an AD that requires the seat rails to be inspected every 100 hours. It adds some cost and inconvenience, as it's a grounding AD. Is there any reason nobody has made STCed seat rails that would eliminate the need for the STC? Is it not possible due to regulations, or is it just that nobody has found it financially feasible to do so due to the costs of FAA approval?

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16 Comments

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ThermiteReaction@reddit

DPEs (dis)qualify airplanes for checkrides with this one simple trick?

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Practical-Raisin-721@reddit

My flight school inspects the seats rail pretty much any time the airplane is down for maintenance, whether it is for the 50hr, 100 hr, annual, or something else.

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odinsen251a@reddit

Having just had to go through the document rigor, I can say I was asked specifically about this AD. "Complied with by inspection"

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ThermiteReaction@reddit

I wasn't asked about it, but one of my DPEs looked at the maintenance record and said "oh, you are really thorough about documenting the seat rail AD" and appeared to assume that everything was good based on that alone.

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Anticept@reddit

If it's STCd replaced, then one can get it AMOCed and discontinue the inspections. Or just write not applicable with each inspection cycle.

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DDX1837@reddit

Why would anyone want to? You would have to design it. Is it going to use the existing seat pins? If so, why will yours not crack and require inspections? If it doesn't use the existing seat pins, now you have to come up with a (cost effective) way to retrofit the existing seats. Now you have to get the STC approved. Finally you can sell it. How much are you going to sell it for? $100 per rail? $200? As soon as the first one gets installed, you're now on the hook for millions in liability claims. A plane with your new seat rail crashes because it flew into a thunderstorm of ran out of gas. Maybe the seat rail failed because it was install improperly. You'll be named in the multimillion dollar lawsuit. So you've spent many years making this new seat rail. You've sold a couple and have generated a couple thousand in income. And now you're pouring 10's of thousands into legal expenses with the possibility of having to pay out lots more. Why would anyone want to do that?

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mtn-predator@reddit

It's just not that big of a deal to add a quick inspection of the tracks and guides with a set of purpose built gauges when the aircraft is already in every 100 hours for inspection anyway, which is going to be the case for flight schools. Most privately owned Cessna never break 100 hours between annuals anyway. For the few that do, again, its really not that big of a deal for someone to do it quickly while waiting for the oil to drain during a normal change. If one does get replaced they are good for another 1,000 hours without inspection. At around $350/track and $150/housing, while annoying, it's not a huge cost by aircraft parts standards, at least not enough that's going to warrant pre-emptive replacement. Replacing the rail and seats/housing with a whole new system would cost a lot and I cannot see that making a good business case for most users.

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andybader@reddit (OP)

I think this is it. My 172 is in a flying club so I’m in the minority (a non-commercial plane that flies a lot). I hadn’t heard about the 1000 hours, though, thank you for that info! Do you have a source handy? I read through the AD but I didn’t see that (although I am reading it on my phone).

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I-r0ck@reddit

It’s in AD 87-20-03 under section 7(d)

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andybader@reddit (OP)

Thank you! I was looking at 2011-10-09, which supersedes the original. I'll save myself a few inspections, hopefully.

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Twarrior913@reddit

The only thing that I do wish the FAA would change on the AD is make it 110 hours instead of 100, so it’d work nicely with the 100 hr + 10 overfly allotment.

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andybader@reddit (OP)

I agree -- I'd love that.

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ckFuNice@reddit

Long ago my 172 had a small seat rail crack, that passed allowable tolerance. But I got new rails anyway, next year from Mcfarlan, sturdier than original, and had the rivets replaced with screws , allowable if approved method done. Easier for future removal, and just better. After I saw the crack, I flew it for couple years, shined a light on there every preflight, added a joe farmer strap , in addition to the existing safety clip stop that had been inserted by previous owner. Had a "crack finder " Aircraft Maintenance Engineer ( Canadian A and P ) . He found a frame crack on my C 150, way in, back left inspection port under rudder. Stop drilled, marked. It had passed a lot of previous inspections, but crack finder bright light good eyes guy was meticulous. I only checked that tail crack for 4 or 5 preflights each time, then every 6th or so flight, because 3 screws, swing plate on 4th to look. The seat rail replacement at the time was about the same cost as a magneto, if I remember. . Another guy decided to redo interior, found a serious show stopper crack above and left of left windscreen after pulling interior paneling (not usually done annually ) Made me wonder how many cracks get missed. Do one thing (seat rails routine hole check , redo interior ). Only soothing thing I guess is 150s, 172s don't crash from missed cracks. So far, anyway. I think they put a 30,000 hour frame life on them, year or 4 ago, so tick tick tick on these old girls I guess. God bless you crew cut slide rule Kansas City airplane engineers .

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SMELLYJELLY72@reddit

horrible liability item right there. that thing goes, the next thing that’s gonna happen is the pilot yanks the yoke and crashes. nobody wants to be responsible for that legal mess. the recurring AD is really CYA for textron to avoid going to court more.

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illeverbe@reddit

Because you have not designed a solution and paid the faa for an stc.

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WingedGeek@reddit

At a guess, no one wants the potential liability.