If that leaves you cold, I have an annotated version. I put the most important stuff in bold, and call your attention to 14 CFR 91.215 as an example. It is a regulation, and says point blank that even transponders do not need to be TSO - they just have to meet TSO requirements. The FAA carefully defines "meet" in their own technical directive to inspectors - both of these are in bold below.
Also note that a lot of this is aimed at whether installing a radio is a major or minor alteration. In the case of the Champs (those that came with radios, anyway) this is a non-issue. The FSDO's position originally was that a non-TSO installation was a major alteration. Almost everything I came up with explicitly and expressly indicated that a com radio in a Cub was simply not a major alteration. Yes, if you have to alter structure (say, a butt rib) that becomes major, but it has nothing to do with the radio.
Here is the annotated version of the regulations and guidance. It tells the story almost without any analysis:
CAR4a – the certification basis for the early Cubs and the Stearman
CAR3 – sort of surprisingly the certification basis for aircraft after about 1948 – the Super Cub is a CAR3 airplane. Comes after CAR 4a.
14CFR 1.1 definition of major alteration
14CFR 43 App A – lists major alterations and discusses altering appliances
AC 43-210 A – has the flow chart that helps determine major alteration status (fig 3-1 & 3-2)
Also speaks to “certification basis” para. 2.2.3.1. Get the latest CHG 1 with commentary.
AFS 300 – Job Aid, Major Repair and Alteration Data Approval
Element D.7 gives examples of “flight critical” equipment
Element D.13 addresses “critical functions”
Element D13l speaks to HSI instruments in part 23 airplanes(!)
Element D13q addresses permanent mounts for GPS etc. – and references “Policy” statement ACE 23-01
Policy Statement ACE 23-01 says, with some caveats about non-interference with other systems and pilots, that a permanent mount can be installed as a minor alteration, and may be connected to aircraft power. Now we need a definition of “portable.”
From PED ARC Final Report 09.30.13:
Portable Electronic Device: A Portable Electronic Device (PED) is any piece of lightweight, electrically-powered equipment. These devices are typically consumer electronics devices functionally capable of communications, data processing and/or utility.
Not sure that helps, but it definitely says the GTR-200 can be used as a portable electronics device. How does a radio become portable? Remove the hold-down device, or replace it with a thumb screw?
AC 43-18 – contains a definition of “critical”
FAR 21.93 – referenced in the flow chart. Defines minor “change” (probably synonymous with “alteration”)
Order 8300.16A – FAA guidance. Also contains the flow chart and clear statements:
1.c. Minor alterations or repairs do not require approved data.
3.2.c.2 – confirm that alteration is “major”
3.a.(1) – determine certification basis
3.3.c . . . show compliance with certification basis ( in our case, CAR4a)
4.1.c – discusses “acceptable data” . . .
4.2c - “If the regulation requires only that an item must be “acceptable to” it does not follow that the FAA requires the item to have specific . . .”
5.2 - speaks to certification under CAR
8.10.a – addresses commercial off-the-shelf articles- “may be acceptable . . .”
8.10.b – addresses section 21.9 and installers.
8.10.c – addresses whether an article must be approved
8.10.c(2) – Acceptable data for minor alterations
Appendix A.10 – definition of “meets” – see 91.215 (transponders)
AC 20-67B – this one is titled “Airborne VHF Communications Equipment Installations”.
Paragraph 1 – one means of demonstrating compliance . .
Paragraph 3 – lists FAR sections, including part 23. Our aircraft are not certificated under part 23.
Paragraph 4 – BACKGROUND – last sentence addresses existing design standards and indicates that “specific systems” may require treatment per AC 20-41A, which itself deals with swapping TSO equipment and flight testing. “Specific systems” requires a definition, and implies a subset.
Paragraph 5 states that if a communications system complies with RTCA DO 186, that becomes “An acceptable means of compliance with the regulations . . .”
The only wiggle room here is that this applies only under IFR, and not to CAR4a aircraft.
Garmin GTR-200 installation manual: The GTR-200/200B transmitter and receiver meet the requirements of RTCA DO-186B (see paragraph 1.3.4) and the GTR-200B is PMA (see paragraph 1.4). The 200B is different only because it is “Bluetooth” enabled.
14 CFR 91.205 and 91.215 address avionics. 205 requires suitable two way radio equipment for IFR flight, with no mention of TSO. 215, on the other hand, mentions TSO for transponder equipment. It does not say TSO is required – it says that the equipment must meet the requirements of TSO. The folks who write these regulations know the difference between “meets the requirements of” and “must be certificated under.” If they had intended to restrict all avionics to TSO only, they knew how to say so. See the definition of “meet” in Appendix A of Order 8300.16A.
Also note the regulations for part 135 operations. Compare the part 91 navigation equipment for overwater flight (just need a nav receiver) to the part 135 requirement of an “approved receiver.” See 91.511 vs 135.165. No statement in 135 requires an “approved” communications installation.
Policy Statement PS-AIR-21.8-1602
This document has almost nothing to do with communication radios, but it does address the ultimate regulatory goal – safety of flight. Its purpose seems to be encouraging the use of safety enhancing items, like angle of attack indicators and self contained attitude indicators. It defines “critical function” clearly (as do other documents). Communication radios do not appear to fall in the critical category. One can (and we do) continue flight after failure of a radio.
And – there was a “working group” set up in the 1990s, producing some work aimed at clarifying the major/minor distinction. The big deal appears to be interpretation of such vague terms as “appreciable effect.” Shouldn’t have any effect on the GTR-200 installation and evaluation – it would be difficult to measure “any” effect on any of the listed criteria with or without the GTR-200 installation, even with sophisticated test equipment. Carrying a water bottle would have more of an effect.
Finally, there has been some discussion of the possibility that the two wires from the portable battery to the radio, through a switch and a circuit protection device, is a “basic change in the electrical system.” That is probably stretching it a lot, but here is the Part 43 App A comment:
(xii) Changes to the basic design of the fuel, oil, cooling, heating, cabin pressurization, electrical, hydraulic, de-icing, or exhaust systems.
So, what is an “electrical system?”
My initial gut feeling is that it is comprised of a source, a regulator, a battery, and a distribution network. Individual elements are not “the system.”
Flight Safety Foundation “Skybrary” defines it that way: “An aircraft electrical system is a self contained network of components that generate, trainsmit, distribute, utilize, and store electrical energy.”
“All aircraft electrical systems have components with the ability to generate electricity.”
CFI Notebook – probably not the most authoritative source: “The primary function of an aircraft electrical system is to generate, regulate, . . .”
And Flying Magazine, likewise not the definitive source, but at least a consensus: “The electrical system wasn’t always so important. In decades past, many thousands of light airplanes had no electrical system at all . . . a battery powered the navigation lights . . .”
Since the FAA has chosen not to define what an “electrical system” is, a mechanic should be free to determine that a battery, a switch, a couple of wires, and a circuit protection device is a simple circuit – especially if the battery is a portable unit.
