Seat rail question

[OkieAviator]

I flew a 182 yesterday and I noticed that the seat rails had a ton of holes in it compared to my 172. I'm assuming because the owner is a tall guy and likes his seat a bit further back that they added more holes.

Assuming they fall within the diameter requirements of the AD is it common to add more holes depending on your seat position?

 

[Norman]

I flew a 182 yesterday and I noticed that the seat rails had a ton of holes in it compared to my 172. I'm assuming because the owner is a tall guy and likes his seat a bit further back that they added more holes.

Assuming they fall within the diameter requirements of the AD is it common to add more holes depending on your seat position?

NOPE!

 

[Dan Thomas]

I flew a 182 yesterday and I noticed that the seat rails had a ton of holes in it compared to my 172. I'm assuming because the owner is a tall guy and likes his seat a bit further back that they added more holes.

Assuming they fall within the diameter requirements of the AD is it common to add more holes depending on your seat position?

Absolutely not. Those rails are considered primary structural parts; they actually form part of the airplane's floor structure. It's the reason AD 2011-10-09 is so fussy about them. I remember one government inspector all ready to take a mechanic to court over a bit of trimming of the forward end of one rail in a 182 to make getting the seat in and out a little less than impossible.

Dan

 

[Stewartb]

My 180's rails can be adjusted back far enough that I can't reach the controls and I'm relatively tall at 6'2". I suspect the 182 rails are just longer than 172 rails, which may explain why they're 3x as expensive. I haven't looked inside a 172 in a long time so I can't remember.

 

[OkieAviator]

Guess that makes sense. If they allowed people to put their own holes in them it stands to reason that someone might make holes down the entire thing ever half inch.

 

[frfly172]

Not going to work ,if you modify the seat rail. That's one reason for the AD.

 

[N801BH]

Absolutely not. Those rails are considered primary structural parts; they actually form part of the airplane's floor structure. It's the reason AD 2011-10-09 is so fussy about them. I remember one government inspector all ready to take a mechanic to court over a bit of trimming of the forward end of one rail in a 182 to make getting the seat in and out a little less than impossible.

Dan

Hmmmmmm....

That is a stretch......

 

[Dan Thomas]

Hmmmmmm....

That is a stretch......

I knew someone wouldn't believe it.

http://www.tennesseeaircraft.net/1964-182-sid-survey-part-3/

A quote:

One might view this as part of the crew seat latching system Airworthiness Directive, but it is a different inspection. It is important to understand that the seat rails are a significant part of the floor structure. Even if no seat were installed, the rails must be in proper condition for complete structural continuity.

Dan

 

[N801BH]

I knew someone wouldn't believe it.

http://www.tennesseeaircraft.net/1964-182-sid-survey-part-3/

A quote:

One might view this as part of the crew seat latching system Airworthiness Directive, but it is a different inspection. It is important to understand that the seat rails are a significant part of the floor structure. Even if no seat were installed, the rails must be in proper condition for complete structural continuity.

Dan

Thanks for the link...

Altho, A couple of seat tracks do NOT equal the strength of longerons, stringers and other critical structural components... IMHO..

 

[Hank S]

Thanks for the link...

Altho, A couple of seat tracks do NOT equal the strength of longerons, stringers and other critical structural components... IMHO..

Longer ones, stringers, etc., shape the outside of the aircraft.

The floor supports the internal load, much more concentrated than the external forces. What support structure is under the thin aluminum floor? Maybe the rails run lengthwise between two formers, transferring the load to the sturdier airframe components without the need for more structure under the floor panel.

I'm just guessing here. My plane has a strong steel frame that everything else attaches to.

 

[Dan Thomas]

Thanks for the link...

Altho, A couple of seat tracks do NOT equal the strength of longerons, stringers and other critical structural components... IMHO..

Open the doors of a Cessna and stand back and look. The airplane is a stressed-skin affair, and those doors knock huge holes in the tube. The wing structure, attached to the carrythrough spars, helps stiffen the fuselage top, but the bottom has very little other than a relatively flat belly skin, the lengthwise ribs, and the floor skin. The rails add to the stiffness of the floor. You'll note that they run from the bulkhead at the aft doorframe to the bulkhead at the forward doorframe.

I have a 177 here right now. The doors on those things are huge and the floor is about half the depth of a 172's. Seat rails contribute considerably.

Dan

 

[Stewartb]

Having had the floor skins out of my Cessnas a few times I'd offer that the sub-floor structure is substantial and the seat rails offer little to it's integrity. Seat rails are there for the seats. Nobody re-skins the underside after a hard landing gear box repair and blames it on seat rails not doing their job.

 

[bnt83]

Open the doors of a Cessna and stand back and look. The airplane is a stressed-skin affair, and those doors knock huge holes in the tube. The wing structure, attached to the carrythrough spars, helps stiffen the fuselage top, but the bottom has very little other than a relatively flat belly skin, the lengthwise ribs, and the floor skin. The rails add to the stiffness of the floor. You'll note that they run from the bulkhead at the aft doorframe to the bulkhead at the forward doorframe.

I have a 177 here right now. The doors on those things are huge and the floor is about half the depth of a 172's. Seat rails contribute considerably.

Dan

Aft seat does not attach to the rails, however, they are attached to at least the forward landing gear bulkhead under that seat. The bulkheads are attached to the aft door post which are directly bolted to the main carry thru spar which is bolted to...

Seat stops installed


Seat stops removed




On this airplane, the sub floor is wimpy. The rails are primary structure.

 

[Tom-D]

Having had the floor skins out of my Cessnas a few times I'd offer that the sub-floor structure is substantial and the seat rails offer little to it's integrity. Seat rails are there for the seats. Nobody re-skins the underside after a hard landing gear box repair and blames it on seat rails not doing their job.

Modify the seat rails, then have any FAA inspector inspect it, see if they don't believe you have made a modification of a structural component.
Those rails hold the seat.. that's structure.

 

[bnt83]

Modify the seat rails, then have any FAA inspector inspect it, see if they don't believe you have made a modification of a structural component.
Those rails hold the seat.. that's structure.

Seat frame is primary structure.

In newer aircraft the seat foam is considered primary structure.

That is all crashworthiness rules.

FAA will want some sort of engineering analysis to approve modifying rails.

 

[Stewartb]

Modify the seat rails, then have any FAA inspector inspect it, see if they don't believe you have made a modification of a structural component.
Those rails hold the seat.. that's structure.

NSS. I said it isn't part of the floor structure. It's there to retain the adjustable seat.

 

[Tom-D]

NSS. I said it isn't part of the floor structure. It's there to retain the adjustable seat.

That's a fine hair your splitting. Those seat rails are riveted to the fuselage structure thru the floor skins on the 100 series. That whole assembly is fuselage, it is like stating a link in a chain is its own structure.

 

[Silvaire]

The thing about the seat rails is that they were always there. In other words, Cessna didn't design the floor structure and then later add them so the whole thing is integral.

As to the AD however, that is all about the adjustable seat locking mechanism and how the holes, pins, rollers and guides get worn. For example, if you install Cessna 150 seats in a Luscombe, which is allowed, the AD comes with them.

 

[Dan Thomas]

As to the AD however, that is all about the adjustable seat locking mechanism and how the holes, pins, rollers and guides get worn.

That AD also talks about permissible cracks: in the top flange only, and only two cracks per rail, max, and no closer than one inch between those two cracks. There cannot be any cracks into the web under any hole, nor in the base flange of the rail, another hint that those rails are carrying more than seat loads.