EricJ

I don't think it would be difficult to make a test fixture to measure that. Measuring brightness wrt the device position isn't conceptually difficult, and the spec should define the test criteria. It turns out that TSO-C30c is based on an SAE spec, AS 8037, which lives behind a paywall. Otherwise we could look it up, but I don't think determining brightness and color at various positions and distances (assuming that's how it's spec'ed) wouldn't be egregiously difficult. Clearly it's been done a number of times judging by the number of LED suppliers in the list for TSO-C30c devices. If the measurements are made at a reasonable distance, the "dark spots" might not matter. If the device meets it, and the assembly that holds the bulb doesn't defeat it (e.g., block any of the required radiation angles), then the system should be functionally compliant.

In the above case I was just citing the TSO compliance as an indication that they'll likely be bright enough to be useful, since some of them out there clearly are not, and at least meet the brightness and color requirements specific for the task of position light. The rest of it is all the subject of the usual discussions, and given the recent citing of the FAA's legal opinion on Preventive Maintenance not being restricted to the Part 43 App A(c) list, probably gonna continue to be open to a lot of interpretation and opinion.

I wasted money on some that were just duds since they were very dim. The ones I wound up with are TSO-C30c compliant (according to the mfg) and are plenty bright, even though they look nearly identical to the duds that were too dim.

I can't find it right now, but I think it specifies brightness, color, radiation angles, etc. It's not complicated but just has to do with the functionality. A bulb can be compliant, which is why many bulbs or bulb replacements cite that spec.

An A&P has no obligation to report issues to anyone but whoever is paying him, unless specifically required to in certain instances (e.g., filing a 337, etc.). Formal inspections results don't go anywhere but the logbook and to the owner/operator, and even then discrepancy lists are given only to the owner/operator and don't go in the logbook. This system is pretty good in that it doesn't discourage people from getting their aircraft maintained or going near an A&P or IA. If there was a risk that the airplane could be grounded or undesirably reported every time it went near an A&P or IA, a lot more maintenance would go underground than already is, and that would be a bad thing.

Yes, the PIC determines the airworthiness of the airplane. However, if the PIC has been made aware of issues that actually materially affect the airworthiness of the airplane and flies it anyway and something bad happens, that could potentially become an issue for the pilot. Personally, I set the bar pretty high on that, i.e., somebody's opinion, that might differ from somebody else's opinion, isn't going to ground my airplane. An AD that has immediate effect and requires immediate action is hard to ignore if you're aware of it, but those are very rare. Almost always an AD gives somebody time to get the airplane somewhere they want it in order to get the compliance work done, and from what I've seen they're usually pretty generous about that. I don't know of any mechanism by which an A&P or even an IA can declare an aircraft grounded. Inspections expire, but that's not done by an A&P or IA. That's my understanding, anyway.

TSO-C30c applies to position lights, so there is a TSO. I believe it is cited in my Mooney IPC or S&M. Some of the LED plug-in replacements claim compliance to TSO-C30c, including the ones I put in. So if you want to cover yourself that way, too, it is possible. I think if you have a decently bright green, red, and white light plugged into the proper socket on the airplane, you're unlikely to get much grief. The main opinion that matters is your IA's.

If you do that it won't be in compliance with the STC and won't qualify as "properly altered" according to the STC or FARs. The guy put himself between a rock and a hard spot.

If you understand torque, the moments are just the torque that that item puts around the datum, wherever that is, due to gravity. If the aircraft were supported only at the datum and all the moments added to zero, it would balance on the datum. This is why the arms are all taken from the datum. It's also why the sign changes in front of the datum, because the torque goes the opposite direction (counterclockwise viewed from the left wingtip for stuff in front of the datum, clockwise for stuff behind it). When you're all done and add up all the torques (moments, with their appropriate signs), there will be a net torque (aka moment) left over. That torque at the datum is from the weight of the aircraft at its center of gravity. So when you're all done adding and subtracting moments, if you divide out the weight of the aircraft from the final moment quantity, you will have the arm about the datum to the center of gravity. It is actually very basic stuff, but seldom gets explained or demonstrated to people in a way that they might understand easily. It is also why sometimes the datum is out in front of the airplane, so that there are no sign changes and errors cannot happen due to a sign mistake. That does, however, make it more difficult to measure an arm for addition of a new item, so there's a tradeoff between making the datum easily locatable and increasing the likelihood of sign errors in calculations.

General wisdom seems to be that since an STC is a change to the Type Certification a 337 is always required. The letter is interesting, but I've never heard of it being cited before. The caveats of "other qualities affecting airworthiness" and "elementary operations" are potential escape routes for the FAA to cause you problems should they decide to, so filing the 337 is the conservative approach when there is a question. I think that's why it's so overdone. The tailbeacon does have an STC with an AML, so whether or not a 337 is filed I think if the installation is done according to the STC the local guy would be disagreeing with the folks in OKC, not the owner or the installer.

I don't think there's anything he can "disapprove", though, if the installation is per the STC, even if he's already been contacted. If the STC permission is obtained, the installation is per the STC, and the 337 is filed citing it, what is there to disapprove? Is this guy gonna fight the FAA guys in OKC that approved the STC?

FWIW, there are a number of example proofs of G5s being installed with IFDs, some owned by frequenters of this very forum. Mine were installed together by a very reputable repair station that was so anal about paperwork that they wouldn't put my NAV1/NAV2 autopilot selector back in because it wasn't on the IFD STC. So go figure. *shrugs shoulders*

I think I used this: https://www.aircraftspruce.com/catalog/elpages/t1284pclens.php Edit: I don't think I used that exact one, but whatever I got, it wasn't very expensive and was a perfect fit for the colored lenses.

But I've spent years building up an immunity to iocane powder.

Are there places that you already have docs for, e.g., DVT, so we don't have to duplicate?