Author Topic: STC for 24 Volt alternator conversion  (Read 6937 times)


STC for 24 Volt alternator conversion
« on: January 14, 2014, 07:04:34 PM »

Anybody have information on whether there is an STC for a 24 Volt alternator conversion? Canadian input would be helpful, since 337's are an issue.

Doug Johnson

Re: STC for 24 Volt alternator conversion
« Reply #1 on: January 17, 2014, 02:07:43 PM »
Little slow to reply couldnt find where I filed the STC for the 24 volt Jasco alternator that was put on c/n 1232.

Take a look at the pdf file attached with the STC for 24V and the 337s, you have to save it and open it later.

Personally, I used a log book entry and didn't bother with a 337.

Most important look at this letter below from Jim Wier an Electrical Engineer.

The installation and operation of pilot-crafted products onto the pilot’s own certificated aircraft has been a source of confusion to mechanics, inspectors, FAA general aviation offices -- as well as to the pilot. Perhaps it might be easiest to clear up the confusion by reference to three FAA documents that bear directly upon the question:
1. “Aircraft Alterations”, a booklet published by the FAA Western Region
2. Advisory Circular 20-62C dated 26 Sep 76
3. 14CFR21. “FAR part 21” -- “Certification Procedures For Products and Parts”
The bottom line of all these references is that there are as many interpretations of what makes a part “legal” as there are persons interpreting the regulations. There is, however, one overriding theme throughout the pages and pages of documentation, and that it is the first person in the installation approval chain -- the installing certificated mechanic (A&P) -- that makes the initial determination as to the type of installation (major or minor) and the paperwork necessary to make an approved installation.
FAA reference (1) above specifically states that it is the installing mechanic that determines whether an installation is major or minor. The document gives two examples -- a simple radio installation in a light single engine aircraft (minor) and a complete radio package including exterior skin drilling for a pressurized turbojet (major). The comment is then made that most installations fall somewhere between these two e xtremes and it is
the EXPERTISE of the installing mechanic that determines whether a simple logbook entry (minor) or major paperwork blizzard (form 337) will be required.
The worst possible scenario occurs when the installing mechanic is not skilled in minor radio installations and asks for help from the Airworthiness Inspector, who in turn calls the local FAA district office for guidance, who refers it to the Engineering Branch, who passes the question on to Oklahoma City, who bucks it up the ladder to Washington for a policy decision...while you wait and wait for an answer. And the whole thing could have been avoided in the first place by selecting a mechanic who specializes in simple radio installations instead of one who specializes in paperwork nightmares.
Fortunately, you have the option of choosing your installing mechanic. If your normal mechanic isn’t skilled in minor radio installations, you will find it to your great time and money advantage to locate a skilled mechanic to perform the installation, perhaps as a consultant to your regular mechanic.
We cannot emphasize too strongly the importance of utilizing the services of a mechanic skilled in minor installations and not major bureaucratic paperwork hassles.
The basic FAR that allows you, the pilot, to build your own avionics is 21.303 (b)(2). To comply with the letter and the spirit of that law, RST kits were designed to be built only by the operator or the owner of the aircraft upon which they will be installed. If you enjoy the thrill of assembling and using your own craftsmanship whileflying, then you are our kind of people. If, on the other hand, you plan on taking this kit to your local electronics shop for assembly, then you are in direct contradiction with both the FAA and RST’s interpretation of part 21.
Although FAR 21 allows owner-pilots to manufacture avionics for their own aircraft without having to go through the PMA/STC/TSO process, somewhere along the line that radio is going to have to be inspected for airworthiness. The Advisory Circular (2) above says that the kits should be inspected:
“ properly certificated or authorized persons to assure that the parts meet all applicable
airworthiness for use on aircraft...”
The best interpretation of this policy guidance we can offer is that your installing mechanic should be on this project from the get-go. We have absolutely no idea what your mechanic’s requirements for inspection are going to be, so a short discussion with the mechanic before you begin construction will pay dividends at the conclusion of your project. We do not recommend bringing the finished, sealed radio to your mechanic and asking for a blessing sight unseen.
RST is very grateful to those of you in the aviation community -- pilots, mechanics, and FAA folks alike -- that believe that by working together in a spirit of cooperation that flying can be made safe and more fun for all of us.
Jim Weir
VP Engineering, RST

Install audio panel 25 Mar Installed RST-504 Audio Selector Panel s/n 14-963 in center radio stack
top of panel using 4-40 hardware and locking nuts. All work performed in
accordance with manufacturer’s recommendations, AC-43-13-1A and 43-13-2.
Fused with 1 ampere fuse. Aircraft must be test-flown before actual IFR flight.
Performance is in accordance with FAR 21.303(b)(2) and FAR 23
New EW -- 1422.8 New EWCG -- 34.6 aft datum New Useful 724.2
James P. Weir Jr. 1750867 A&P
SAC VOT 3 -2 Test flight audio panel 27 March Test flown on
SAC ILS. Operation of audio panel and marker beacon normal. All audio
switching functions normal and test OK. All radios check OK
for further flight.
Gail Lathrop 2722203 Commercial
Owner - Pilot

When I was putting My Helio back together, I had an engine with a 24v starter and a 12v 100 generator that wouldn't fit because the new firewall didn't have an indentation required for it to fit. it also weighed about 35 lbs and it also had a carbon pile Linear voltage regulator that weighed 15 lbs also a huge Alkaline battery under the front seat. None of which I liked other than the starter.

I knew I could get twice as many watts with 24 volt 60 amp alt ver 12 volt 60 amp alternator so I elected to go that route. I also went with a solid state Linear voltage regulator. Because a Linear voltage regulator extends the life of the RG batteries.

The 12 volt wire in place will carry more amps at 24 volts also so no need to totally rewire if the wire is already the slick white modern version. All you have to do is change the bulbs and I strongly recommend taking the time to do the paperwork to install the new LED variety low watts low heat not affected by vibration and they last practically forever.

Hope to get some feedback from you guys.


« Last Edit: January 17, 2014, 02:21:10 PM by Doug Johnson »


Re: STC for 24 Volt alternator conversion
« Reply #2 on: January 17, 2014, 09:01:36 PM »
A couple of points.
1. Robert is in Canada and I believe he needs to have an STC, not a US 337.
2. The JAARS STC SA987SO does not include a 24 volt alternator.
3. JAARS has done form 337 field approvals based on their STC SA987SO for a few 24 volt installations.
4. That 337 does not give anyone approved data to do your own, however, you can use it as a basis to get FAA field approval if your FSDO still does them.
5. Anyone using an STC MUST have the STC owners permission in writing to use it or you are in violation of CFR 91.403.
6. CFR 43 Appendix A is the standard to which an alteration, minor or major, is determined, and yes a mechanic can make that determination but he has to be able to "defend" it based on that document.
Jim Metzler


Re: STC for 24 Volt alternator conversion
« Reply #3 on: January 19, 2014, 09:30:30 AM »
Thanks Doug and Jim...we are probably in the hunt for the 24 Volt Generator then until we get the import out of the way.

Doug Johnson

Re: STC for 24 Volt alternator conversion
« Reply #4 on: January 19, 2014, 10:30:23 PM »
Just curious what is the status of C-FEFT c/n 2533 or are you using it for parts to build c/n 1295.

Just had a thought maybe next time you're in the States you can replace your 24V gen with a 24V alt using a field approval. Might be a good excuse for a trip to Alaska, I hear they are still doing field approvals there.



Re: STC for 24 Volt alternator conversion
« Reply #5 on: January 20, 2014, 09:10:22 AM »
#2533...still look at it every now and again...since we started to put together #1295, the 250 is a more extensive project for sure. I would like to tackle that one day, however, the 295 is well underway.

Because of the strict rules regarding an import, we have to be very careful to make sure there are no changes/mods (other than STC'd) on the plane to be imported. My AME works very closely with the import designate (who is very detailed)
To give you an example - the plane came with new sound insulation and reflective material when the firewall was installed in Phoenix. We had to make a difficult decision to remove and replace with a material that would pass the import. Even something as simple as the tires that the plane came with,  7.00 x 8 tires, need to changed to 6.50 x 8 (as per the manual)
We will have to put back the 24 Volt generator on for the import, and will likely change it at a later date.

A trip north sounds good..we hope to have the plane rolling by June/July this year.