The International Cessna^® 170 Association

They are talking about this on the Stinson yahoo site. If correct it could prove to be valuable.-


While going thru IA renewal class I came across the following.

all appproved 337s prior to Oct 1, 1955 are still valid as FAA approved data when filling out a new 337.

This information is not new but I was not aware of it and thought I would share it with the group for what it is worth. If we had a list of all 337s approved prior to the above date it could be helpful to some.

Just to clarify what Cy said for those that do not "get it" yet, a pre Oct of 55 form 337 is considered "approved data" just like an STC or PMA. You reference that old 337 in a log book entry and you are done, no need to hope the Feds sign off on your modification. Done. You do, of course, have to do the work exactly as was done for the old, approved 337. Change it and you are on your own to get a modern 337 approved.
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I am told (by my aquaintance who has a restoration shop) that the logic of it is that before that date, the FAA knowlege pool was much deeper than it is now, and that anything they approved in those days was basically subject to a pretty good engineering review by the FSDO sign-off process. That is no longer the case (as many of us can vouch for, when trying to deal with the current FSDO types) and a 337 approval does not have as much technical "weight" behind it anymore.

Mike that would be great if our planes were a bit older and the pool of 337s a bit larger. I looked specifically for this reason at al of them. Of all the 337s in our library I recall only one being prior to that date. It is to remove the venturi and install oversized inspection holes behind the right rear seat belly. (sounds like a camera port to me)

It may be merely an unfortunate choice of words but referencing an old 337 "in a log book entry and you are done" .. is not exactly correct. Major alterations still must be documented with Form 337 and submitted for approval. However, FAA may accept that previous 337 as sufficient data for approval of the subject airplane's alteration. (They also may NOT....if they believe the old 337 did not adequately document the exact method and materials of the alteration.)

Before making ANY major alteration to your airplane, unless an STC exists for the work, it's wise to discuss the matter with an FAA inspector or FSDO having jurisdiction.

George
Here is another quote off the website. I think where you might find alot of pre 55 337s are Alaska registered aircraft. If you ref a older 337 the work must follow it to a t. and a 337 filed ref the older one as approved data.

You’re mostly right, Larry. The older 337 with the engineer’s signature is approved data. Newer field approval 337’s are acceptable data. FAA Order 8900.1 Vol. 4 Chapter 9 covers selected field approvals and the process. That is available via Google. Just type 8900.1 and go to that chapter. That is the FAA inspector’s handbook. Great info there.

8900.1,chapter 9,sec 1. It states 337 filed before the 1955 date are aproved data. If you do a mod exactly like that 337 it is considered approved data. It would be nice to have a list of all these older 337s on file. Could be interesting. Starting with the 1948 model their could be some useful mods. It might pay for everyone on a cold winter night for grins to look thru their records.