STC: 337 vs Logbook Entry

455 Bravo Uniform

455 Bravo Uniform

Final Approach
Joined
Aug 18, 2015
Messages
5,769
Location
KLAF
Display Name
Display name:
455 Bravo Uniform
I've searched previous posts and I'm still unclear.

Simple question: a modification is done that has an STC for said aircraft - is a logbook entry sufficient, or does a 337 need to be done?

If for some reason the next three posters all agree, the mods should lock this thread so there aren't 5 pages of confusing and conflicting responses.
 
Going to ruin it right from the start....

Rosen Visors... there is an STC (for many makes/models). But... there are A&Ps who would classify this as a minor logbook-only modification and not bother with the 337. Others would insist on doing the 337.

So, it depends.
 
337 signed by an IA. No FAA sign-off required but the 337 still gets filed with the FAA.
 
STCs need a 337 filled out and approved by a mechanic with an inspection authorization.
 
I agree with Jeff. If you want to use the STC as your basis to install it in the aircraft, then you need a 337 filed before returning to service.

There was no STC for the Navion and the Rosens. Rosen sold me a 310 mounting kit and told me how to cut the acrylic blades if needed. My mechanic and I were content with claiming it was not a major modification and she signed off the installation in the log book.

About the only downside to the installation is that I had opened the box when it arrived to examine them. I had put the box in the rear seat of the Navion and parked it on her ramp in front of the hangar doors. She decides to move the aircraft so she hops in the plane without closing the canopy and fires up the the engine. As she advances the throttle it blows the packing peanuts in the Rosen box all over her hangar.
The language that ensued reminded me that she had served in the Navy.
 
337 with an IA signoff....and it gets sent in to OKC.

The reason for the 337....it's an addition to the type certification (a supplemental) that requires an addition to the aircraft records.
 
Well specifically, the FAA considers anything done via an STC to be a major alternation hence 337 NOTICE OF MAJOR REPAIR & ALTERATION is required. Of course, in most cases, you can ignore the STC and just do it as a minor alteration. There's nothing magic about sunvisors.
 
A vendor can't sell an aircraft part as an aircraft part without a PMA. Since it isn't a direct replacement part it requires an STC and AML. The fact that a mechanic deems it a minor alteration has nothing to do with the manufacturer requirements. Most STCs are more complex than a goofy piece of tinted plexi.
 
Brackett air filter comes to mind. For a whopping $30, you get the entire kit, for a Cherokee 140, complete with STC paperwork.
Just swap the old paper filter with the gooy filter. Easy peasy. No major changes to anything.
 
Stewartb said:
A vendor can't sell an aircraft part as an aircraft part without a PMA.
Click to expand...
That's not strictly true. There are several different ways to manufacture an approved part, PMA is but one of them.
Since it isn't a direct replacement part it requires an STC and AML.
Click to expand...
That's not true.
The fact that a mechanic deems it a minor alteration has nothing to do with the manufacturer requirements. Most STCs are more complex than a goofy piece of tinted plexi.
Click to expand...
True, but what's the point. Just because there's an STC for something in some situations doesn't mean that it isn't the only way to legally install it.
 
Anybody have the reg handy that stipulates a 337 is required for all STCs?
 
The way I read it, 21.113 essentially defines an STC as altering a product via a major change that does not require a new type certificate. If you are installing something, and using the STC as the installation approval, you are in essence altering the type certificate of the thing you are applying the STC to. This makes it a major alteration and as such, requires a 337.
 
Agreed. A 337 is required to document the installation of an STC.
Sometimes people say they're doing things "on a 337" when they're talking about a field approval.

On the other hand, things that can be done based on the type certificate can be done with a log book entry. You can go from a E-185 to an IO-520 on a Navion just by following the manufacturers data and make a log book entry.
 
Haha I googled this, and found a lengthy thread with plenty of disagreement on the topic......here on POA! (It ended with the OP threatening to down a handful of pills with liquor after 3 pages, if that tells you anything about the answer.)

PS it did, I think, imply that not all parts out there truly needed an STC but the manufacturers decided that there was so much rancor over the issue that they decided to just get one so everyone would do a 337. If I'm reading it correctly.
It also stated that some parts out there are STC'd (337) but they are also PMA (no 337) for other applications so that might also result in some confusion.
 
Let'sgoflying! said:
Haha I googled this, and found a lengthy thread with plenty of disagreement on the topic......here on POA! (It ended with the OP threatening to down a handful of pills with liquor after 3 pages, if that tells you anything about the answer.)

PS it did, I think, imply that not all parts out there truly needed an STC but the manufacturers decided that there was so much rancor over the issue that they decided to just get one so everyone would do a 337. If I'm reading it correctly.
It also stated that some parts out there are STC'd (337) but they are also PMA (no 337) for other applications so that might also result in some confusion.
Click to expand...

Yeah, it's subject of much disagreement. But I think it comes down to what one is using for installation approval. Speaking of disagreement, I wanted to comment on your "PMA (no 337)" statement :) PMA is a manufacturing approval, not an installation approval. Garmin G5's are PMA'd, but installed under an STC, mostly due to it probably being easier than getting folks to consider it a minor alteration. To install something in a certified aircraft you need 2 things, the part to be approved through some means (TSO, PMA, NORSEE, owner produced, etc) and a means to install it (minor alternation, equivalent part, STC). For example, McFarlane has a lot of PMA'd parts that are equivalent parts, with the documentation that goes along with that. Some PMA'd parts one might consider a minor alteration (like Rosen visors), and install them as such even though they have an STC. Some have STC's to make the installation approval even clearer (G5s). But that's all of course, just my interpretation!
 
Last edited:
Understand the inclusion of something under an STC is a major modification. Filing the 337 is perfunctory as the STC gives you the authority to do it and the person providing the STC almost certainly has approval to make the parts.

PMA just says they have the authority to make a part (possibly for a specific set of aircraft). Usually, this is sufficient as the installation of the part doesn't fall into the definition of a major modification.

Yes, there are some goofy things like the Rosen visors that have STCs even though they'd hardly be considered a major mod. Since Rosen doesn't have an STC fo the Navion, I just installed the 310 version in mine as a minor mod.

Remember there's three things you need to have to put something on the aircraft:

1. Approval to put this on your particular aircraft (either it's under the TC, or an STC, or a field approval, or it's a trivial mod or common part).
2. The part has to be approved for manufacture for aircraft (the production certificate parts of a TC/STC, a PMA, an TSOA, owner produced parts, accepted MILSPEC, etc...).
3. The person who does it has to be qualified and fills out the right paperwork.
 
flyingron said:
Yes, there are some goofy things like the Rosen visors that have STCs even though they'd hardly be considered a major mod. Since Rosen doesn't have an STC fo the Navion, I just installed the 310 version in mine as a minor mod.

Remember there's three things you need to have to put something on the aircraft:

1. Approval to put this on your particular aircraft (either it's under the TC, or an STC, or a field approval, or it's a trivial mod or common part).
2. The part has to be approved for manufacture for aircraft (the production certificate parts of a TC/STC, a PMA, an TSOA, owner produced parts, accepted MILSPEC, etc...).
3. The person who does it has to be qualified and fills out the right paperwork.
Click to expand...
Actually there is a misunderstanding, Rosen Visors are a major modification, that is why they went the expense of gaining an STC.
But their STC does not include the Navion, So the installer must gain a Deviation to the application list, by the Field approval method.
Or by having Rosen add the Navion to the application list.

And it is all recorded on a 337, by the description in block #8
 
From my personal experience (having submitted an aircraft to a designee for export inspection) any STC that is applied to the aircraft needs a filed 337 (even if not inherently a major alteration). It's easy to do the paperwork and submit it.

I can also tell you from personal experience, that when submitted to the Aircraft Registration Branch they are simply scanned and added to the permanent aircraft records. I accidentally sent the wrong copy in once (unsigned) and yep, it was added to the permanent aircraft records. Could I get them to remove and replace with a signed copy? NO, but they were happy to add the signed copy to the file if I sent in the corrected one (which I did, of course)...

The STC paperwork signifies a change in type design, and of course the paperwork itself drives the 337 (not the actual change to the aircraft). Of course, getting the STC approved was the part supplier's method of gaining FAA approval to manufacture those parts for use on certified aircraft. So, one process spawns the other....
 
flyingron said:
How is a sun visor replacement a major modification? This is silly.
Click to expand...

It seems like some of the manufacturers are using the STC process as a tool to get these seemingly minor modifications approved for sale. The Bogert battery cable STC is a good example of this, there is a Piper service bulletin addressing the problem and gives you a list of materials to fabricate your own cables, but the Bogert cable kits still are STCd.
 
mondtster said:
It seems like some of the manufacturers are using the STC process as a tool to get these seemingly minor modifications approved for sale. The Bogert battery cable STC is a good example of this, there is a Piper service bulletin addressing the problem and gives you a list of materials to fabricate your own cables, but the Bogert cable kits still are STCd.
Click to expand...

Exactly!
 
Banjo33 said:
Does 337 sent to OKC also require a logbook entry?
Click to expand...

Affirmative. There may be exceptions that I am ignorant of, but a logbook notation should be made for the date, time, what was done, part/tag numbers if appropriate, etc, and signature/very # of an A&P and/or IA as necessary.
 
My favorite is that I have a binder with a half a dozen flight manual supplements for a plane that doesn't have a flight manual.
 
The installation manual for the Garmin 335 ADS-b transponder states it is a minor alteration. Logbook only entry.
 
Floyd said:
The installation manual for the Garmin 335 ADS-b transponder states it is a minor alteration. Logbook only entry.
Click to expand...
The installation manual for any avionics does not include the structure changes that may be required . Not all aircraft have the 5.25" center stacked radio rack.
Even when they do these old racks have been drilled so full of holes it is impossible to fit a new slide in tray.

(Replaced instrument panel structure to facilitate new radio installation.). = major repair.

Plus if there is a W&B change There should be documentation on that.
 
Last edited:
This is from the GTX 335 with GPS install manual.
Install the panel mount GTX 335 with GPS as a minor alteration in accordance with FAA Memorandum
Installation Approval for ADS-B OUT Systems or FAA Notice 8900.362 Policy for Installation of
ADS-B OUT Systems using the data in this installation guidance manual. Installation in accordance with
the FAA Policy Memo only pertains to the GTX 335 with GPS and limited interfaces contained herein.
Bottom line is just because something has an STC does not make it a major alteration.
 
Floyd said:
This is from the GTX 335 with GPS install manual.
Install the panel mount GTX 335 with GPS as a minor alteration in accordance with FAA Memorandum
Installation Approval for ADS-B OUT Systems or FAA Notice 8900.362 Policy for Installation of
ADS-B OUT Systems using the data in this installation guidance manual. Installation in accordance with
the FAA Policy Memo only pertains to the GTX 335 with GPS and limited interfaces contained herein.
Bottom line is just because something has an STC does not make it a major alteration.
Click to expand...
so....how does that STC become part of the aircraft record?
 
OK, so what kind of paperwork needs to be filed to replace the control wheels in a Cessna T-50, with yokes from a Lockheed C-130?
 
bluerooster said:
OK, so what kind of paperwork needs to be filed to replace the control wheels in a Cessna T-50, with yokes from a Lockheed C-130?
Click to expand...
Is there an STC?
If not, a field approval will be required. How much the flight control system must be modified will be described in block #8
 
IIRC, it was a simple remove one, and install the other. No modification needed.
 
My view is that manufacturers like Rosin do the STC just to shut people up and put a lid on the inevitable endless bickering. You can install them as a minor with log entry if you want, just don’t reference the STC but yes, if you choose to incorporate the supplemental type certificate you need to file the 337.
 
Silvaire said:
My view is that manufacturers like Rosin do the STC just to shut people up and put a lid on the inevitable endless bickering. You can install them as a minor with log entry if you want, just don’t reference the STC but yes, if you choose to incorporate the supplemental type certificate you need to file the 337.
Click to expand...
I beg the difference, It is one A&P's fear of getting hammered by the FAA who thinks it is a major.

Bob Hover syndrome
 
flyingron said:
How is a sun visor replacement a major modification? This is silly.
Click to expand...

And so is a 337 silly for installing an LED landing light.

Major alteration means an alteration not listed in the aircraft, aircraft engine, or propeller specifications -

(1) That might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or

(2) That is not done according to accepted practices or cannot be done by elementary operations.



Minor alteration means an alteration other than a major alteration.
 
You must log in or register to reply here.
Back
Top