C172 337 for HID Landing light - FAR Question

sshekels

sshekels

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Scott Shekels
I am an a quest to obtain a 337 to allow me to install a XeVision HID landing light in my C172. The physical process appears to be straight forward, however I have a question about the 337.

I submitted my idea to a local (and very helpful) Minneapolis FSDO inspector a couple of weeks ago, and received a reply today. He addresses a few points where I did not fill in the form correctly, and one final item that I am unsure how to address. "FAR 23.1383(a)(b), glare and halation must be addressed." Specifically, how does the HID light effect glare and halation?

How in the world does one address that? The location of the bulb in the 172N is in the lower cowl, so that helps. Prop arc may be an issue, but the distance between the bulb and prop is small, so again that would be a help. One could do a real world test (without flight), but that seems extreme.

Thoughts?

Scott
 
We ran around a similar question when folks started putting the Q4509 halogen bulbs in their Grummans instead of the standard tungsten 4509's. While some FSDO's had signed off on Q4509's on a 337 as a field-approved alteration, others refused much as what's referenced in your note. However, nobody ever met an FAA inspector who looked at their plane and said, "AHA! That's a Q4509, not the regular 4509 that's supposed to be in a Grumman -- you're BUSTED!" and nobody thinks they ever will.
OTOH, the LoPresti "Boom Beam" light system for the Grumman comes with an STC, and without that you don't put one in -- it goes on a 337 as a "major alteration" but as it has an STC, it does not require FSDO approval, just review of the 337 to ensure you did it per the STC.

Not being familiar with a XeVision HID light, I don't know where that falls between installation of the "Boom Beam" (replacing the whole landing light assembly) and putting in a halogen bulb designed as a replacement for the original tungsten bulb with the same number, just preceded by a Q.
 
I believe the XeVision is the SAME device as Lopresti, right down to the ballast. It appears the same, just significantly cheaper - like $500 to $700 less.
 
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sshekels said:
I believe the XeVision is the SAME device as Lopresti, right down to the ballast. It appears the same, just significantly cheaper - like $500 to $700 less.
Click to expand...

Well, in that case, it's probably a "major alteration" requiring an STC or field approval documented on a 337. Since LoPresti ships the STC with the unit, maybe that's the difference -- they did the paperwork for you, and that costs extra.
 
Yup. They do the work, and you pay. I'm trying to go cheap, and I think I almost have it through the FAA. I'm just stuck on how to address the glare issue...

I guess the easiest is call and ask!
 
sshekels said:
Yup. They do the work, and you pay. I'm trying to go cheap, and I think I almost have it through the FAA. I'm just stuck on how to address the glare issue...

I guess the easiest is call and ask!
Click to expand...

I'm trying to understand how the heck a non-coherent light source is going to affect the generation of halos (or glare for that matter). Those effects are a function of the optics between the reflecting target and your eyes AFaIK.

This is probably resolvable by performing and documenting some sort of test. The FAA loves data, even if they don't understand it.

I work with several very good optics guys, perhaps they have some ideas for you. I'll ask Monday.
 
Cool! Thanks Lance!

I came up with the idea that the light has a narrower horizontal beam angle (10 vs 12 degrees), and identical vertical beam angle (10 degrees) as the original light. Given it has the same form factor, it should not be an issue.

I think they are concerned about reflections off the plane (not an issue, as its the original location) and the higher intensity (500K candles, vs. 290K).

My thought is the higher power is not that much of an issue, due to the inverse square law...

Thanks for the help Lance!
 
As a person who has field approve this type of installation in the past it's not as hard as some think. I had to contact our regional engineering office for assistance, but using e-mail and the telephone most field appovals can be accomplished in a few days time. I would be willing to provide FREE training on field approvals at the Oakland Airport if enough owner/mechanics are interested.

With Spring/Summer upon us Oakland (OAK) would be a nice vacation place. We are hosting the Navion 3 day fly-in-training May 20-22. If you get a time the Business Jet Center is hosting the event this year at the Oakland airport. We will be discussing field approvals and I will be on hand to assist owners with their aircraft.

Stache

Stache
 
Stache, I am SO close to getting this done. Just some minor errors on my part, and this whole "glare halation" issue.

How does one address that with the FAA? My current idea is, the location is the same, so it is shielded from cockpit view/glare from the cowl, and while the light output is greater, it is not significant due to the inverse square law...

Thanks!
S.
 
sshekels said:
Stache, I am SO close to getting this done. Just some minor errors on my part, and this whole "glare halation" issue.

How does one address that with the FAA? My current idea is, the location is the same, so it is shielded from cockpit view/glare from the cowl, and while the light output is greater, it is not significant due to the inverse square law...
Click to expand...

Scott, I ran the issue by a couple of the optics folks here, and while none claimed any significant expertise WRT halos and glare" the consensus was that the most likely issue would be operating in the presence of mist/fog.

Perhaps you could take a picture from the cockpit into 1/2 mile haze with the existing lamp and the new one and present this as "evidence" that there's no problem.
 
The glare issue is one from the propeller and the other rain/fog. The fix was simple as we had to tilt the light down to provent the glare. It's like having your head lights on high beam. Turn it to low beam or tilt the light and it works fine. This took sever flights to get right. I am currenty in Oklahoma City right now, but I have the data in the office we used. If you can wait a week or so I will look it up for you.

Stache
 
Piggy-Back Theory: If the LoPresti light is truly the same as the XeVision light, I would ask the FSDO if you can reference LoPresti's STC for the C-172 in your 337, or obtain a copy of LoPresti's application for its STC and attach it to your 337. I assume the STC application is public record.
 
I've always wanted to put wing-tip lights on the T206H, but I'm not sure what would one do with the one in the wing. I guess you could leave there and only use for Taxi and the brighter wing-tip lights for take-off and landing.

It's Friday ! :goofy:
 
Interestingly enough STC info is NOT public. It is protected as "trade secret" unless you can demonstrate to the FAA you are unable to contact the owner.

The FAA guy I am working with is REALLY nice. We chatted yesterday, and his comment was that I should install the light and try it at night (on the ground) and make a comparison to the original. If the glare / halation is not an issue. Done deal.
 
sshekels said:
Interestingly enough STC info is NOT public. It is protected as "trade secret" unless you can demonstrate to the FAA you are unable to contact the owner.

The FAA guy I am working with is REALLY nice. We chatted yesterday, and his comment was that I should install the light and try it at night (on the ground) and make a comparison to the original. If the glare / halation is not an issue. Done deal.
Click to expand...

Imagine that, a quick practical test. Makes sense.
 
If an STC is available and the owenr does not want to purchase the STC the FAA can not accept the data. However if the owner has a letter from the STC holder stating it is okay to use their data then it is a different story.

I have field approved STC data that was not for the make and model the parts were installed. In some case the STC holder will allow this because of the cost in adding a different make and model on their STC effective list. However make sure and get it approved from the STC holder before submitting your 337 to the FSDO.

Stache
 
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