Is it ok to paint an aircraft antenna

[737mechanic]

I work for an airline and we replace many DME and VHF antenna's for paint erosion or chipping and I would like to be able to touch up the effected area's of the antenna but there are people that say you can't paint them. I have looked and looked and have not seen anything that says you can't paint them nor have I been able to find where it says you can unless I go by the standard painting practices in the maintenance manual.

From what I have learned the antenna's are painted with polyurethane and that is what we would be using to touch them up so I see no reason why we couldn't.

Can anyone give me anymore information on this issue.

 

[ScottI2R]

737,
I have talked with a couple of people, one an A&P for NWA at this time and a retired Maint. Supervisor for NWA. Both these guys I know quite well and they both told me that they DO NOT paint antennas on aircraft. Pete, the current A&P told me last night that it is S.O.P. to just replace them.

Hope this helps.

Scott

In a hundred years, it isn't going to matter anyway.

 

[WWIIPlaneGuy]

Painting Antennas and Radomes is like speeding on interstate--you shouldn't but most people do.
I have never known any operator to notice a reduction in antenna gain or radar accuracy due to paint, but in a lab you can usually see a definite reduction in capability from a field -painted antenna or radome.

 

[737mechanic]

I found in the overhaul manual for the TCAS antenna the procedure to paint it, so we are going to start painting them with no problems, Funny thing is the TCAS is much more important to aircraft safty then VHF or DME and the manufacturer doesn't say anywere you can paint them.

 

[rerig]

Could be we used Zinc Chromate primer on everything...once upon a time. Not good for Antenna.

And in keeping with the "We've never painted Antenna" theory, why reinvent the wheel now that we are using epoxy primers and topcoat. Yes, there is some degradation of transmisivity on radomes, but should not bother UHF/VHF.

But try to get the OEM to re-think painting antenna. Might as well ask Congress if it is OK.

 

[737mechanic]

Yea I think the "You can't paint antenna's" come from the old days when some paint was lead based and the antenna manufacturer would use special paint which is what we use today as normal paint. The paints used by antenna manufacturers back then and now are either epoxy or polyurethane.

I have heard that some airlines have in there MPM the procedure for painting antenna's and I have also found on the net a Navy document "NA 01-1A-22" that is titled "Aircraft Radomes and Antenna Covers" that has procedured for painting antenna's. If anyone can find the actuall Navy document somewere I would like to read it and see what it has to say.

My most compelling argument I see is why would it be ok for the antenna manufacturer to be able to paint antenna's but not anyone else even if they are using the same paint. After all there is paint on the antenna's when we put them on our airplanes. One anwser would be maybe the antenna manufacture wants to sell more antenna's

 

[Higgler]

Well,
As an antenna engineer with some great test equipment, if anyone wants to send me a painted and non painted antenna, a simple test takes just 10 minutes and it's easy to do, and I won't charge you anything (other than return shipping). You could also send me the paint for loss tests, that'll cost you a bit, I'd have to make a test setup special.

In general, low frequency wider bandwidth antennas can be painted with most non metallic paints and you'll never see the difference.

The worst antenna to paint is a narrow band antenna (GPS antenna is best example) using a thick paint coating. It'll shift the frequency downward and not work in your frequency band anymore.

Narrow bandwidth (typically thin antennas = narrow bandwidth) antennas, if designed properly should have a thick radome so that multiple thick paint coatings (or rain/ice) will be far enough away from the metal radiating part of the antenna to be out of the field.

On the same thought pattern, water is dielectric = 81, and very high loss, much much higher than 99.999% of all paints. That's the worst paint equivalent (other than metallic paint) that you can imagine. If it works in the rain, generally it'll work with a little extra paint on it.
kchiggins
Toyon Research Corporation
Antenna Group.