The International Cessna 170 Association

I am putting an Innovation Airframe single rear seat in my c170. Directly behind the seat and about 14 inches back is a nut plate. I believe it is for a 3/16 bolt. Is this strong enough for attaching the belt (both sides)? I have not been able to get clear information on this.

The original rear seat was attached to the airframe by four bolts, one on each side of the seat, one directly under the seat, and the bolt that engages that nut plate you describe behind and centered in the airframe side-to-side. The four seat belt attach points were on the seat frame assembly itself but did not connect directly to any seat attach bolt. A structural analysis would have to be done to get a definitive answer and that has not been done as far as I know on the 170. You will have to decide if it can safely be done.

But, to help in your decision, the C185 with separate rear seats, have their center rear seat belts bolted directly to that same center attach point you describe.

Richard, does the B model 170 have cargo tie down nutplates back behind the backseat on either side?
I know on my '56 172 there are either 2 or 4 nutplates (I think 4) with two of them being forward and the other two being farther back. I just don't remember how far back. Just wondering if those, if they exist in the B model and are far enough back, might be as strong as the back anchor on our factory rear seats? I once made a couple of homemade, screw in tie down anchors from some steel stock and threaded the end so it would screw into the aft anchors. Since I don't weld, I used brute force and a vise to bend both anchors into loops. Only used them once to hold some tool boxes, etc. and they seemed adequate.

The nut plate I am thinking of using is not for the seat but 1/4 of the way in from the side and parallel with the seat nut plate.

Since those seats are PMA copies of Cessna 180/185 middle row seats it would seem that using the same method and attach points for the seat belts that Cessna uses in the 180/185 would be the easy solution rather than trying to reinvent the wheel. Take a look at the mid 60's and newer parts manual.

Tim

170C wrote:Richard, does the B model 170 have cargo tie down nutplates back behind the backseat on either side?..............

Frank, I'm not familiar with the nut plates you are referring to, sorry.

dogone wrote:I am putting an Innovation Airframe single rear seat in my c170. Directly behind the seat and about 14 inches back is a nut plate. I believe it is for a 3/16 bolt. Is this strong enough for attaching the belt (both sides)? I have not been able to get clear information on this.

It's really difficult to know what you're describing (or even to determine if what you're describing is common to all models... maybe you have a unique situation?) ...without a picture. Does the Innovation Airframe people have an answer for you?

I would not be putting my life on the line for a single attach point for a seat belt. I know some people will say a 3/16 screw has a breaking strain of such and such but it’s only a sample test that’s done over thousands made. And they are allowed 5 to break in the sampling test. Reason is I have just been through this exercise as we purchased a number of AN bolts and there was a number of them with mal formed heads. The paper work was all correct so off to the authorities I went . The only bolt that’s standard is guaranteed is a NAS that’s been magafluxed and has a dye marking green on it. The supplier replaced the bolts and was informed by the authorities that this situation was ok. I was informed it’s up to the certified person fitting the parts to make sure all parts have the correct documentation and parts are of a standard as per the manufactures manuals.

ghostflyer wrote:... I was informed it’s up to the certified person fitting the parts to make sure all parts have the correct documentation and parts are of a standard as per the manufactures manuals.

Here in the U.S. the PIC is responsible for determining whether the aircraft is in condition for safe flight. (FAR 91.7b). I’m sure we’ve all confirmed that none of the AN3-5A bolts on our planes have “MAC X” markings on the head as outlined by SEB96-7.

Gary fair enough statement, but I think most would take a step back and look at the big picture. I think it takes a “ system “ to determine whether a plane is safe for flight.

The Airframe Innovation website seems to provide the answer to the seat belt attach question:

"FAA Design Approval for seat belt attach hardware for older Cessna models has been included in the STC."

dogone wrote:I am putting an Innovation Airframe single rear seat in my c170. Directly behind the seat and about 14 inches back is a nut plate. I believe it is for a 3/16 bolt. Is this strong enough for attaching the belt (both sides)? I have not been able to get clear information on this.

My '52 170B has three 1/4" nutplates on the floor at station 90; one on centerline and two approximately 11" from centerline. It also has two 1/4" nutplates approximately 8" from centerline on the floor at station 108. These are shown in the IPC fig. 23-60.

Wow! That would be nice having all those tiedown options, my 1951 170A has nothing other than the original rear seat attach bolt nutplates.

n2582d wrote:My '52 170B has three 1/4" nutplates on the floor at station 90; one on centerline and two approximately 11" from centerline. It also has two 1/4" nutplates approximately 8" from centerline on the floor at station 108. These are shown in the IPC fig. 28-60.

Mine has these as well in what sounds like the same locations.

lownslow and n2582d ; you have what I have been trying to describe. I am not near my AME and was just trying get clear in my own mind if the other hard point was good for the belt. I am not yet familiar with the Cessna original placement. I hope to clarify when I talk to my AME.