I frequently get asked "Do I need a 337?" by callers asking about mods and repairs underway.N9149A wrote:Bill,
I have L-19 wings but I didn't put them on and it was done under a 337 not an STC. ...
If you ... just had to have the hard points for the rocket pods like mine do, then you may have a valid reason to want to use it on a 170.
This is a major point and one which I'd like to make in the interests of universal edification. I know Bruce knows. I know a lot of you know. But this is an excellent place to say (from a non-lawyer/non-regulator point of view):
A "337" refers to FAA Form 337. This document is required to be completed when any "Major Alteration or Repair" is accomplished and that is the title of the document. One original of the document is kept with the aircraft maintenance records (logbooks) and one original is sent to the FAA in OKC for permanent filing into the FAA records.
The Form 337 has several sections or "blocks".
Block "3" of the Form 337 is ordinarily left blank when major alterations and repairs are supported by appproved or acceptable data/methods/materials such as structural repairs documented by the original manufacturer or designee (DAR/DER), or repairs are accomplished according to FAR 43.13, or alterations are performed according to an already approved STC, or the replacement of a Cessna 170B wing with another identical Cessna 170B wing.....on a Cessna 170B.
Block "3" is completed/required to be signed (approved) by an FAA inspector whenever an alteration or repair is made using methods/materials not previously meeting those requirements for that particular airframe, such as the replacement of a Cessna 170A wing/flaps with a L-19 wing/flaps, or alteration of L-19 wing-flaps to 170B flaps, or the installation of rocket pods on a Cessna 170 wing of any model.
When Block "3" is completed, that is commonly referred to as a "Field Approval", which in effect is approval and documentation of a change to that particular aircraft's type design. (The change from one model wing to another would require this unless it were accomplished under the authority of another approval basis such as STC or mfr's service bulletin, etc.) A "Field Approval" is not transferrable to other aircraft, even of the same make/model. Each aircraft so modified will require it's own approval. (The fact that Bruce's 170A is fitted with L-19 wings and B-model flaps does not provide authority to make that alteration to any other Cessna. However, an FAA inspector might accept Bruce's data as a basis for making another identical approval.) He may not.
I'm not an FAA lawyer, but that is a layman's description of what a "337" is and it's purpose. It documents Major alterations and repairs, and if those alterations and repairs are not accomplished according to accepted methods/materials then the alterations/repairs must be approved and Block 3 must be completed.
It is NOT satisfactory to make a major alteration to an airplane with no basis of approval other than what the owner wants and assume it is OK because a "337" talks about it. Form 337's do not of themselves "authorize" anything. They only support documentation, therefore a major alteration is not simply done "under a 337" although that phrase is commonly issued to indicate that the alteration has been documented. Is it approved? That's a different matter.
I once had a Cessna 206 with a whole pile of 337s that the FAA had no record of. There are lots explanations for that sort of thing, everything from "the FAA probably lost it" to "the U.S. mail probably still has it" to "the dog ate it". If an aircraft has a major alteration or repair, unless the 337 is in the aicraft's records then the aircraft's records are incomplete. And unless the work described thereon is acceptable and/or approved it is illegal. A signature of an FAA inspector in Block 3 is an indication that the alteration or repair has been approved by that inspector and is "good to go". Otherwise the work must meet the aircraft's type certificate or other approved basis for that airframe.
As for my old 206, ... Some of those alterations were simply performed by an unscrupulous "mechanic" with no approval basis whatever and the only existing copy was in the aircraft records. I believe that "mechanic" simply filled out 337's and gave them to the previous owner to satisfy the ignorant that the work met an approval basis....when in reality it met NO approval basis...and that he deliberately did not send a copy to FAA-OKC so as to not raise any questions up there. (It had a Cessna 185 engine/prop installation instead of the correct ones. If OKC had been in receipt of that information they doubtless would have considered revoking the Airworthiness Certificate of the airplane and the Repairman certificate of the "mechanic". The owner of the aircraft might have been at risk of fines/penalties as well as any pilot who'd operated that aircraft.) The previous owner had accepted that mechanic's subterfuge thinking it was legitimate, but the OWNER is who is responsible for making certain the aircraft meets it's type design or "approved alternate" design. That mechanic bamboozled him. It cost him plenty when it came time to perfect the sale of that aircraft to me. He jumped through expensive hoops in order to keep the authorities from getting involved in that matter.
Bruce... got any rockets?
