When is an STC required?

[DKandle]

23.93 “minor change” is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product" and anything else is a major change.
A major change requires an STC (per 21.113)
The installation of a GPS would seem to be minor. So, why do they all have STCs? Even a Rosen sun visor has an STC. How can that be considered a major change?

 

[Tom-D]

First thing, is it a major or not. (your A&P will know).


the major is called from the get go.
the major changes are already called.
File to 337s they are already approved.

 

[bnt83]

23.93 “minor change” is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product" and anything else is a major change.
A major change requires an STC (per 21.113)
The installation of a GPS would seem to be minor. So, why do they all have STCs? Even a Rosen sun visor has an STC. How can that be considered a major change?

for starters
https://fsims.faa.gov/wdocs/other/Major_Repair_Alteration_Job-Aid.pdf

 

[Bob Noel]

23.93 “minor change” is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product" and anything else is a major change.
A major change requires an STC (per 21.113)
The installation of a GPS would seem to be minor. So, why do they all have STCs? Even a Rosen sun visor has an STC. How can that be considered a major change?

to nitpick a bit: A major change to the type design requires an STC. There are other acceptable means to make a modification to a specific aircraft.

 

[Bell206]

How can that be considered a major change?

There's been a number of threads on this topic that contain all your answers. But to sum it up, a major change to type design (Part 21) is not the same as a major alteration (Part 43). As to STCs, there are basically 4 different types, each with their separate requirements regardless of what it covers. Not all STCs are considered major alterations (337 requirement) with some STCs considered a minor alteration (logbook only requirement.) Several FAA documents explain this in more detail.

Any chance you're related to EdFred and his multiple personalities? Seems to be a number of one post wonders in recent times that rehash old topics.

 

[DKandle]

for starters
...

Thanks. This provides the answer. It appears that a GPS is considered to have an appreciable effect on "operational characteristics" of an aircraft and that is how it is considered a major alteration. On the Rosen question that was made to see if anyone could actually justify that STC. I've asked the FAA several times on that one and gotten different answers. One answer is that by definition, if something has an STC then it is major. Others say no, it isn't major ignore the STC. Others say just file the 337 because some IA down the line may just want it done.

 

[unsafervguy]

bell hit it, but another reason is marketability. too many A&P IA's really do not understand the major/minor, need for a 337, and need for a stc rules very well. a lot just cover there a... but saying "if it ain't stc'ed or have a tso, it ain't going in". manufactures know this and are willing to spend the extra dollars need to get and STC to open up that market.

 

[Tom-D]

Thanks. This provides the answer. It appears that a GPS is considered to have an appreciable effect on "operational characteristics" of an aircraft and that is how it is considered a major alteration. On the Rosen question that was made to see if anyone could actually justify that STC. I've asked the FAA several times on that one and gotten different answers. One answer is that by definition, if something has an STC then it is major. Others say no, it isn't major ignore the STC. Others say just file the 337 because some IA down the line may just want it done.

Remember you must file a 337 to get it entered into the history records for the aircraft. This constitutes a change even though it is only for records.
a 337 may be entered and it is not a major change, for example a change to Weight and balance maybe entered simply a way to make a permanent record.

 

[Stewartb]

If a guy creates a simple part like a Rosen visor and wants to sell it as an airplane part he'll need an approval. An STC allows the STC holder to install the part. A PMA allows him to sell it for others to install. It's a parts manufacturer's rule. To the owner of the plane it may be a minor alteration. If they sold the same part for "experimental use only" you can still install it if it's a minor alteration.

 

[unsafervguy]

Thanks. This provides the answer. It appears that a GPS is considered to have an appreciable effect on "operational characteristics" of an aircraft and that is how it is considered a major alteration. On the Rosen question that was made to see if anyone could actually justify that STC. I've asked the FAA several times on that one and gotten different answers. One answer is that by definition, if something has an STC then it is major. Others say no, it isn't major ignore the STC. Others say just file the 337 because some IA down the line may just want it done.

no, a gps does not have an effect on operational characteristics of an aircraft. operational characteristics apply to the aerodynamic or systems operation of the aircraft not the procedures you use to fly it. thousands of gps units were put in with nothing more than a log book entry for years.

 

[unsafervguy]

Remember you must file a 337 to get it entered into the history records for the aircraft. This constitutes a change even though it is only for records.
a 337 may be entered and it is not a major change, for example a change to Weight and balance maybe entered simply a way to make a permanent record.

sorry tom, stuff like that is why the 337 system is so screwed up. you want to change the empty weight in the records, write it in the log book. it does not need to be put on a 337. the "you need a 337 mentality is way out of hand, and I blame A&P's for making it that way, to many have no real clue as to what needs a 337 and what doesn't. I responded to and A&P on another board that insisted that any alteration or change required a 337 just last week.

 

[Bell206]

On the Rosen question that was made to see if anyone could actually justify that STC.

To add to the above posts, in order for someone to produce/sell an article that could be installed on a type certificated aircraft (or marketed to same) those parts must be produced per some sort of FAA approval (21.9).

In the case of the Rosens or other similar articles (Concorde batteries, etc) that could be installed across a number of TC aircraft, vendors will usually select the AML-STC process as that base-line design approval can used on multiple TCs vs using a PMA/TSO process which requires a separate specific approval for each TC model and variant.

Unfortunately, an STC is only a design approval and not a production approval so most use the PMA or TSO process for the production approvals. That is why you will see PMA/TSO stamps on STC parts. So the reason Rosens have an STC is for the base-line design approval. And considering the installation of the Rosens may involve attaching the visors to primary structure, Rosen leaves it up to the installer to determine if it is a major alteration or not.

One answer is that by definition, if something has an STC then it is major.

If that were the case, then why are there STC certificates that state, in black and white, the STC is a minor alteration in the “Conditions and Limitations” section? Not all STCs are created equal.

 

[DKandle]

And considering the installation of the Rosens may involve attaching the visors to primary structure, Rosen leaves it up to the installer to determine if it is a major alteration or not.

If that were the case, then why are there STC certificates that state, in black and white, the STC is a minor alteration in the “Conditions and Limitations” section? Not all STCs are created equal.

I can't use a link - (per this site's restrictions on new members) this is from www.faa.gov/aircraft/air_cert/design_approvals/stc/stc_app/
An STC will not be issued to:

• approve minor changes, or for approval of identical replacement parts, unless the installation of such parts constitutes a major change to the type design

As noted in my post - I've asked the FSDO and FAA at Oshkosh about this particular mod and gotten several answers. At our last IA meeting someone asked specifically the question "does the existence of an STC imply that the change is major" the answer (from the FSDO's ASI) was yes it does. Obviously this subject is both complicated and ambiguous.

 

[Bell206]

At our last IA meeting someone asked specifically the question "does the existence of an STC imply that the change is major" the answer (from the FSDO's ASI) was yes it does.

In my experience, you'll find that not all ASIs will have the same experience levels especially if they do not interact with the MIDO or ACO on a regular basis which not all do. Also, some ASIs group all STCs into one group, even though there are several different types, for simplicity as a majority of the general aviation public do not know that fact either or pursue STCs in general. And considering only the ACO can review/approve STCs (not the FSDO) it's usually easier for the ASI to simply stick to the single STC mantra and hope you'll go away.

But for discussion sake, print out the link below for your next FAA IA meeting and ask the ASI to explain the statement on page 3. There are other examples as well. However, it's important to keep the terminologies in their proper format: major/minor change to type design vs major/minor alteration. This is important because even a major alteration can still be classified as a minor change to type design. Isn't this fun.
https://www.mcfarlaneaviation.com/media/documents/doc-sp00582ny.pdf

 

[Tom-D]

sorry tom, stuff like that is why the 337 system is so screwed up. you want to change the empty weight in the records, write it in the log book. it does not need to be put on a 337. the "you need a 337 mentality is way out of hand, and I blame A&P's for making it that way, to many have no real clue as to what needs a 337 and what doesn't. I responded to and A&P on another board that insisted that any alteration or change required a 337 just last week.

When the owner can not find the W&B, we get to weigh the aircraft again. Dumb

 

[unsafervguy]

When the owner can not find the W&B, we get to weigh the aircraft again. Dumb

if there is not a current W&B in the aircraft and paperwork you have to re-weight it anyway, thems the rules. just getting what the FAA has on file does not cut it unless what the FAA has on file contains the current configuration in it. sorry, If i don't have a WB that agree with the current configuration then its going on the scales before my name and number goes in the book. but that would take more than 20 minutes......

 

[unsafervguy]

In my experience, you'll find that not all ASIs will have the same experience levels especially if they do not interact with the MIDO or ACO on a regular basis which not all do. Also, some ASIs group all STCs into one group, even though there are several different types, for simplicity as a majority of the general aviation public do not know that fact either or pursue STCs in general. And considering only the ACO can review/approve STCs (not the FSDO) it's usually easier for the ASI to simply stick to the single STC mantra and hope you'll go away.

But for discussion sake, print out the link below for your next FAA IA meeting and ask the ASI to explain the statement on page 3. There are other examples as well. However, it's important to keep the terminologies in their proper format: major/minor change to type design vs major/minor alteration. This is important because even a major alteration can still be classified as a minor change to type design. Isn't this fun.
https://www.mcfarlaneaviation.com/media/documents/doc-sp00582ny.pdf

thanks bell206, thats a good one to have in my files for reference about this subject.

 

[Tom-D]

sorry tom, stuff like that is why the 337 system is so screwed up. you want to change the empty weight in the records, write it in the log book. it does not need to be put on a 337. the "you need a 337 mentality is way out of hand, and I blame A&P's for making it that way, to many have no real clue as to what needs a 337 and what doesn't. I responded to and A&P on another board that insisted that any alteration or change required a 337 just last week.

Anyone take a bet there are other things that the FAA wants put in the HISTORY RECORDS..

How many times do we see bills of sales, liens, and other documents.

"unsafervguy", thinks I'm screwed up, When the FAA wants this recorded. And remember the 337 recording system is called the History file, It is all the same file.

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The Aircraft Registration Branch maintains registration records on individual aircraft and serves as a repository for airworthiness documents received from FAA field offices.

 

[Bell206]

"unsafervguy", thinks I'm screwed up, When the FAA wants this recorded. And remember the 337 recording system is called the History file, It is all the same file.

Well, when the FAA does want something recorded they're pretty straight forward in telling you where, when, and how. In the case of an aircraft W&B, the FAA plainly states in the TCDS the current W&B report, along with a current Equipment List, must be in the aircraft. The other documents you mention that can be found in the Aircraft Record each have their own process to follow which does not include the use of a 337. If the concern is lost records, why stop at only the W&B record? Or should we include the required records in 91.417 on a 337 as well? As to unsafervguy's assessment, I think he pretty much summed up the situation in a nutshell.

As a side note, the existing FAA guidance on the purpose of a Form 337 is pretty straight forward which I believe covers mainly 3 conditions, none of which is to record a W&B. And when the use of a 337 is required outside that guidance the FAA provides the requirements in another guidance document like for the ADS-B Flight Test 337. So unless you have some FAA guidance I'm unaware of to use a 337 outside of the established requirements you run the risk of that 337 being discarded/returned for improper use, or worse get a nasty-gram from the Feds telling you not to use a 337 in that manner as one operator I know did.

 

[Salty]

The short answer to the original question is: when the AP or APIA that is going to sign off the work says it is.

 

[Stewartb]

Find a better IA.