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STC’s and 337’s

Richgj3

Richgj3

BENEFACTOR
LI,NY
For you A&P/IA. If a part comes with an STC is a 337 always required or are there cases when a log book entry is sufficient?

I fully understand this may vary from FSDO to FSDO based on opinions. I would like to hear your comments.

Examples: McFarlane flap roller upgrade kit for Cessna 100 series. Comes with STC. Appears no real difference from original part. My A&P says no 337 needed.

BAS shoulder harnesses for Cessna 170B. It installs using an existing nut plate in the carry through. Comes with an STC. I haven’t done this one yet.

These two things would not be “major alterations” in my mind, but I don’t have the license.

Thanks
Rich
 
An STC is an approval for a major alteration and major alterations requires a 337. If an item is a minor alteration it does not require an STC and a log book entry will do it.
 
Also depends on the part. Is the part made under a PMA or an STC? Ca;; McFarland and ask why they have an STC.
 
If an item has an STC, and that item hasn’t been rolled into the TC, then yes it does require a 337. Most times the STC isn’t rolled into the TC as an STC is owned by someone other than the TC holder, but sometimes they are. An example of this is ABI 3200 on American Champion. ABI STCd the tailwheel on the American Champion airplanes, then American Champion rolled the tailwheel into their TC. So now you can install an ABI3200 tailwheel on any one of the American Champion airplanes with a log book entry even though there is an STC as well.


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Richgj3 said:
For you A&P/IA. If a part comes with an STC is a 337 always required or are there cases when a log book entry is sufficient?.......
Examples: McFarlane flap roller upgrade kit for Cessna 100 series. Comes with STC. Appears no real difference from original part. My A&P says no 337 needed.
BAS shoulder harnesses for Cessna 170B. It installs using an existing nut plate in the carry through. Comes with an STC. I haven’t done this one yet. ...
Click to expand...

I would guess that the McFarlane rollers are not approved on the TCDS as a replacement for Cessna rollers--
maybe Cessna would have to give the approval?
Hence the STC ("supplemental" being the key word) under which they are approved.

BAS harnesses: the FAA has issued a policy statement approving shoulder harness installations as a minor.

Issuance of Policy Statement, Methods of Approval of Retrofit Shoulder Harness (faa.gov)

However, the PS has certain parameters, including:
"A retrofit shoulder harness installation may receive approval as a minorchange in these small airplanes if:
The installation requires no change of the structure (such as welding ordrilling holes)..."

The BAS reels mount to the stock nutplate in the spar carry-through, yes,
but also a couple bolts go up thru new holes the web of the carry-through & the roof skin.
Hence an STC is required.
 
My understanding is that if you have to use an STC for an installation approval then by definition it is major modification (modifying the TCDS installed equipment) and requires a 337

The only things not requiring a 337 are PMA/TSO parts that are listed on the TCDS or are deemed identical to factory equipment (PMA) or lastly are direct replacements of previously STC (with 337) installed components. IE if you had Bushwheels installed under STC already and are replacing them with any other Bushwheel listed on the AML for your aircraft then it's simply a logbook entry and update the W&B if the new tires differ in weight from the old ones.

Speaking with a friend who is an A&P/IA/DER about 337's he said he sends one in whenever it's even a question if it should be filed or not. For one the 337 goes on the permanent record for the aircraft's modifications so any future potential purchasers of the aircraft can look up the modifications during a prebuy and be sure they were done legally which helps resale. Also the 337's aren't heavily scrutinized by the FAA in any case since they have so many coming in they normally just rubber stamp them if they have an STC number or other supporting documentation listed. All the mechanic is doing is notifying the FAA of a major change under previously approved STC which the FAA appreciates in any case since all too often mechanics cut the FAA out of the feedback loop because they're afraid of attracting any FAA attention. Bureaucracy runs on paperwork so just keep feeding the beast.
 
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You can't just send a 337 in (well, you can, and nobody looks at them for validity any more) - you need "approved data." The DER may be able to generate that, but an IA cannot.

As far as I can tell, approved data for a 337 with the "major alteration" box checked can only be from an STC, a Field Approval, a pre-1955 337 for another airplane, or from a previous field approval issued to the same IA for an identical aircraft.

You cannot just describe a major alteration and mail it in.

I agree - if you have an STC in your hand, fill out a 337. It is almost free.
Always check the definition of "major alteration."
 
I have knowledge of only one STC that specifically states in the instructions "no 337 required". Prop Guard Tape. Never did understand that.
 
bubb2 said:
I have knowledge of only one STC that specifically states in the instructions "no 337 required". Prop Guard Tape. Never did understand that.
Click to expand...

I have another oddball one for you - Cessna Rosen sun visors. These are a minor alteration, log book entry all day long, but for some reason Rosen felt compelled to obtain an STC.
 
By strictest interpretation of the regs, something installed under an STC should be just a log book entry. I.e., items covered by the type certificate can be installed with log entry only. And as the title calls out, items approved for installation by STC (Supplemental Type Certificate) are approved by the feds. But over time the, feds have required a 337 with an STC installation for documentation. And now it's being used as an easier avenue for producing/selling items than getting a PMA stamp.

My favorite example is the Attlee beacon mount for the rudder on Cubs. If I fabricated one of these from scratch, I'd install it with a log entry. But somewhere along the line they got an STC for that. Same goes for the McFarlane flap rollers, as mentioned above. They should be PMA'd all the way as they simply replace the existing rollers and hardware

Web
 
How about radio installs? My aircrafts paperwork has elaborate 337's describing the installs of various TSO'd radio packages over the years.
 
Not a major unless you cut into structure to mount them or tie them into a major system like navigation.

Web
 
Richgj3 said:
..Examples: McFarlane flap roller upgrade kit for Cessna 100 series. Comes with STC. Appears no real difference from original part. My A&P says no 337 needed.

Thanks
Rich
Click to expand...

wireweinie said:
...But over time the, feds have required a 337 with an STC installation for documentation. And now it's being used as an easier avenue for producing/selling items than getting a PMA stamp.

Same goes for the McFarlane flap rollers, as mentioned above. They should be PMA'd all the way as they simply replace the existing rollers and hardware

Web
Click to expand...
My take:
1/ McFarlane decided to build some flap rollers.
2/ Cessna would not give McFarlane a copy of the original flap roller drawings so that McFarlane could make a direct copy.
3/ So, McFarlane made their own drawings and had the FAA issue McFarlane an STC to install the rollers on certain airplanes. (These rollers may just happen to be a 100% direct copy of Cessna's rollers. But they were not made in accordance with Cessna's drawings.)
4/ In order for McFarlane to manufacture and sell these rollers for their customers to install under the STC on their airplanes, McFarlane had to acquire a Parts Manufacturing Approval.
5/ SO: Since an STC (major alteration to the type certificate) was issued, a form 337 is required to install the PMA parts which McFarlane is selling along with the STC (permission to install).

Now had Cessna given McFarlane a copy of Cessna's drawing to use, McFarlane could have just had the FAA issue them a PMA for the rollers in which case the rollers would have just been a minor equipment substitution. Log book entry by A&P only.
 
wireweinie said:
Not a major unless you cut into structure to mount them or tie them into a major system like navigation.

Web
Click to expand...
You should have been in the room at an annual IA meeting when Bill O'Brien stated a 337 was required for radio installations. Most of the IAs cried fowl. Particularly after some of us had been told by our FSDO that no 337s were required for radio installs. It was clear by the discussion that there are many radio installations which disagreed with Washington DC FAA's interpretation. My PMI was sitting right next to me, he shrunk down in his seat. 8)
 
Thank you everyone. Pretty clear now. I got the mechanic to do a 337. Turns out in the case of the flap rollers, the STC applies to the one “special roller” which replace the Cessna part. So, that is done and I learned something.

I also understand the requirement for a 337 for the seat belts. And, when I bought this 170B it already had Rosen visors installed and the 337 is in the paperwork. :)

So, as you say, easy enough to do. I just needed a little background before I talked to the A&P about doing one. He was happy to do it when I asked.

Rich
 
What if you're replacing your aging incandescent landing lights with LED's? Is only one 337 required to change them out or do you need a different 337 for every landing light on your plane, even if you're using the same type of LED light for all them (mine has 4).
 
Narwhal said:
What if you're replacing your aging incandescent landing lights with LED's? Is only one 337 required to change them out or do you need a different 337 for every landing light on your plane, even if you're using the same type of LED light for all them (mine has 4).
Click to expand...

That's a great question....they're light bulbs, fer crying out loud....and, according to the regs, even I am qualified to change a light bulb.....and I'm NOT qualified to submit a 337.

Then there's "Door Stewards" for Cessnas....STC'd, so this requires a 337?

Or Rosen sun visors.....

ad nauseum. So, I guess the question is: Is there ANYthing that is actually considered by the FAA to be a "Minor alteration"? Maybe putting PMA'd air in a tire?

MTV
 
Narwhal said:
What if you're replacing your aging incandescent landing lights with LED's? Is only one 337 required to change them out or do you need a different 337 for every landing light on your plane, even if you're using the same type of LED light for all them (mine has 4).
Click to expand...

I do landing lights as minor alteration, log book entry only. Use the flow chart in AC43-210A to arrive at that answer. I love using FAA supplied policy to make my life easier.


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dgapilot said:
I do landing lights as minor alteration, log book entry only. Use the flow chart in AC43-210A to arrive at that answer. I love using FAA supplied policy to make my life easier.


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Click to expand...

The subsequent landing lights or even the initial LED replacement? The Whelen LED comes with an STC so based on everything said here it’d need a 337, which is what we did. I’ve only put in one LED so far.

I’m just a pilot though.

I was threatened with a violation by an FAA airworthiness inspector during a ramp check because they claimed my rented Cessna did not have an STC for the Rosen sun visor. They let me go with a warning.
 
skywagon8a said:
You should have been in the room at an annual IA meeting when Bill O'Brien stated a 337 was required for radio installations. Most of the IAs cried fowl. Particularly after some of us had been told by our FSDO that no 337s were required for radio installs. It was clear by the discussion that there are many radio installations which disagreed with Washington DC FAA's interpretation. My PMI was sitting right next to me, he shrunk down in his seat. 8)
Click to expand...

This is one of the problems with FAA. The pendulum keeps swinging, and what needed field approvals 20 years ago is now done with log book entries, but it is starting to swing back again. Best thing is simply use the guidance FAA publishes along with the regulations. Definitions in Part 1, definition of “major type design change” in 21.93, Part 43 Appendix A, AC43-210A, Order 8300.16, Order 8900.1Volume 4 Chapter 9, and AFS-300 job aid. Document your decision process using this guidance, and it is surprising how much can actually be minor alterations.


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How could a ramp check possibly have access to your 337s?

As as far as I can tell, only aux. fuselage fuel tanks require that the 337 be on board.

On the radio installations, are they field-approved? No wonder the feds want DERs to do all the field approval work.

I am putting a GTR-200 in our J4 almost as I type. It will be logbook entry, powered by a portable battery.
 
dgapilot said:
This is one of the problems with FAA. The pendulum keeps swinging, and what needed field approvals 20 years ago is now done with log book entries, but it is starting to swing back again. Best thing is simply use the guidance FAA publishes along with the regulations. Definitions in Part 1, definition of “major type design change” in 21.93, Part 43 Appendix A, AC43-210A, Order 8300.16, Order 8900.1Volume 4 Chapter 9, and AFS-300 job aid. Document your decision process using this guidance, and it is surprising how much can actually be minor alterations.


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Click to expand...

Thanks for those references. I learned something today: changing seatbelts is preventive maintenance and I can do it on my own plane.

So many little worries that get answered here.
 
bob turner said:
How could a ramp check possibly have access to your 337s?

As as far as I can tell, only aux. fuselage fuel tanks require that the 337 be on board.

On the radio installations, are they field-approved? No wonder the feds want DERs to do all the field approval work.

I am putting a GTR-200 in our J4 almost as I type. It will be logbook entry, powered by a portable battery.
Click to expand...

CFI checkride at a FSDO so I brought the logs. I didn't stick around to hash out the details after they "let me off with a warning". I called the owner, told him what happened, and had my girlfriend come pick me up. I went to a different FSDO the second time and had no problems. This was all ~ 20 years ago.
 
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Something else to consider, a TSO is a design approval and a manufacturing approval (TSOA), but it is not an installation approval. To install a TSO article, you may need additional Approved Data if it is a major alteration. PMA (Parts Manufacturer Approval) is a design approval, manufacturing approval and installation approval (limited to those products identified in the PMA). An STC (Supplemental Type Certificate) is a design approval, and an installation approval, but not a manufacturing approval. If an STC holder wishes to sell parts for his STC, he needs to also get PMA for those parts, and the PMA installation approval will be only for products that have been modified by that STC.

PMA can be done as identical except to the original part, a new design to replace an original part, or a new design to install a different part. Discussion of thing like sun visors that never existed in the original product need STC as the design basis for the installation. Seems silly, but adding things to an airplane without appropriate approval violates the definition of airworthy (meets the type design or properly altered state, and is safe for operation) the first part of the definition is the hardest to wrap your head around. The Type Design is the set of drawings and reports that the original manufacturer submitted to FAA or CAA. If you stray from that, now you need to look at 21.93 to define if it is a major or minor change to type design.

21.9 limits the sale of parts that may be installed on aircraft. If a part can reasonably be expected to be installed on a Standard aircraft, in order to sell it, you need to have either a Production Certificate, a PMA or a TSO.

Hope this helps to understand how FAA rules for parts work.


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Narwhal said:
CFI checkride at a FSDO so I brought the logs. I didn't stick around to hash out the details after they "let me off with a warning". I called the owner, told him what happened, and had my girlfriend come pick me up. I went to a different FSDO the second time and had no problems. This was all ~ 20 years ago.
Click to expand...
I had a similar experience with a 709 check ride and a Husky that was only a few years old. Unairworthy because a jury strut bolt creaked when they shook the wing. Wouldn't let me tighten the 3/16" bolt there. Had to get a ferry permit, fly it home, fix it and reschedule. They aren't happy till we aren't happy.
 
Steve Pierce said:
I had a similar experience with a 709 check ride and a Husky that was only a few years old. Unairworthy because a jury strut bolt creaked when they shook the wing. Wouldn't let me tighten the 3/16" bolt there. Had to get a ferry permit, fly it home, fix it and reschedule. They aren't happy till we aren't happy.
Click to expand...

Yep, and it was probably at one of the same FSDO's from my story (the plane was based in central texas).
 
skywagon8a said:
You should have been in the room at an annual IA meeting when Bill O'Brien stated a 337 was required for radio installations. Most of the IAs cried fowl. Particularly after some of us had been told by our FSDO that no 337s were required for radio installs.....
Click to expand...

Several years ago, I replaced the crappy old radios in my C150/150TD with a nice new Icom A200.
My IA buddy was gonna supervise & sign it off.
He checked with his PMI (who was a friend of mine, a great guy, and very reasonable & common sensical re issuing field approvals)
who told him a 337 was required.
And if the radio was TSO'd, the IA could sign it off,
but if it wasn't TSO'd it would need a field approval.
The first & only time I've ever heard that.
Icom sold both a TSO'd & non-TSO'd version of that radio, so I just bought the TSO'd one--
making the paperwork go easier was well worth the hundred bucks more that it cost.
 
hotrod180 said:
Several years ago, I replaced the crappy old radios in my C150/150TD with a nice new Icom A200.
My IA buddy was gonna supervise & sign it off.
He checked with his PMI (who was a friend of mine, a great guy, and very reasonable & common sensical re issuing field approvals)
who told him a 337 was required.
And if the radio was TSO'd, the IA could sign it off,
but if it wasn't TSO'd it would need a field approval.
The first & only time I've ever heard that.
Icom sold both a TSO'd & non-TSO'd version of that radio, so I just bought the TSO'd one--
making the paperwork go easier was well worth the hundred bucks more that it cost.
Click to expand...

Show me the FAR that requires that.

Web
 
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