TSO

Found it:

edburkhead.com/Ercoupe/TSO_Instrument_Requirement.htm

I am quoting from a message that was posted on the tech list. Names have been removed to protect the innocent. BTW, I think these documents are on Ed Burkhead's site. Unfortunately, I don't remember the URL right now.

"As you may remember, I have fought the issue of TSO-Non-TSO at least 3 times (radio, altimeter & ASI) and won. When each of those happened, I posted the documentation, which included e.g. letters from the FSDO conceding the point, which I used to reassure the avionics techs, A&Ps, etc., that the only instrument which a VFR Ercoupe 415 needs to have TSO’d is the transponder. For example, the non-TSO’d ASI must meet the same standard that was required when our planes were certified under the C.A.R.; if I recall correctly now (without digging out the documentation again) that standard was something like +/- 5 mph.

"If someone who knows how to search our archives would like to pull those postings up, I’d gladly give permission for them to be put on some more permanent, easy-to-access web location for everyone to access, such as Hartmut’s &/or the EOC (IIRC, in fact, I think Ed Burkhead may have put some of it on his website…but it has been long ago so I don’t recall the details). Sorry, it just takes me too long to find those things over again in my own electronic files after 10 years of Ercoupe ownership, to do so each time the TSO-Non-TSO issue comes up again (every year or two).

"Having said that, I did run into one radio shop who said that their own insurance policy prohibited them from installing anything that was not TSO’d, no matter how legal it was. So, law or policy analysis aside, one can’t expect a shop to buck its insurance carrier if they are adamant. Fortunately, I found others who were not, and happily installed anything I could demonstrate was legal.

I guess you ask 4 people you'll get 5 answers. Linda Abrams in California went through a long process figuring out if she could put a non-TSO radio in her Ercoupe. The conclusion drawn was that she could. This is one of the biggest headaches with a bureaucracy like the FAA (or IRS). It seems that the rules are so poorly written that they can be interpreted multiple ways, and if you're checked it's the luck of the draw whether you are legal or not.

it does not have to be TSOd. We've been through a lot of discussion on this, and anything other than the transponder and encoder do not have to be TSOd.