The Cessna 120-140 Association Forum

All of the fuse holders in my 120 are junk with a mangled mess of wire to go along with them..Can circuit breakers be used as replacements without a huge paperwork event?

scotts97385 wrote: ↑Thu Sep 22, 2022 7:43 pmCan circuit breakers be used as replacements

Yes.

without a huge paperwork event?

Well, that depends.

Here's the deal. Part 43 Appendix A spells out what constitutes a "Major Alteration". By definition, if an alteration is not a major alteration, then it is a minor alteration and can be accomplished with only a log book entry. The relevant wording from Appendix A is "changes to the design of the electrical system" (are major alterations.) So, if your IA agrees that replacing fuses (circuit protection devices) with breakers (also circuit protection devices) does not constitute a change to the design of the electrical system, then all you need is a log book entry.

If your IA feels the need to file a Form 337, you can cite the data in AC43.13-1b Chapter 11 Section 4 as approved data and no further approval should be necessary. You should consult this section regardless to ensure your choice of circuit breakers is appropriate; you can't always e.g. replace a 20 amp fuse with a 20 amp circuit breaker.

Scott, John is right. I am an A&P with IA and just finished (well almost) the restoration of a 47 C-140. I replaced all the old fuses with circuit breakers and just entered it in the logbook with the rest of the work done during the rebuild. A major alteration is defined in the FARs and is basically any change from the original design that does not involve any structural member, control system or flight characteristics. All other changes are considered minor and only require a logbook entry. The change from fuses to CBS is in my opinion a no brainer. By the way, flew my 140 last Monday for the first time.
Steve Hawley