On some airplanes, the black on the radar dome is a glued on black rubber abrasion boot and that’s what it looks like on the MD
The nose of a radar dome takes a beating due to erosion from hitting rain at 300 or more knots, so sometimes operators will use a rubber boot or a plexiglass cap on the nose of the radar dome to protect it. Radar domes are usually made of layers of fiberglass but nowadays could be made from layers of composites. It could be that AA
is now using a strong erosion paint or some other form of erosion protection on the nose of the radar dome.
On fiberglass radar domes, one of the main problems is when the surface becomes porous due to erosion or cracking of the paint, water then can get between the fiberglass layers and freeze up at altitude, effecting the radar returns. If water gets into the fiberglass, then the radar dome has to be removed, and dried out either by baking in an oven or using heat lamps, then sanded down, resealed and repainted, a time consuming process, so the outside of the radar dome must be kept water proof.
I have seen different ways to protect the nose of the radar dome. On the JetStar we had a hell of a time keeping paint on the nose of the radar dome, we used to have to touch it up every couple of months. First we tried a thin rubber cap, but it lasted only a few months, so we finally had a pre molded plexiglass nose cap glued on and that took care of the erosion problem.
Just in case anyone is interested, on the MD
-80 radar dome you can see thin strips running from the nose to the back of the radar dome, they are metal strips for lightening protection. Radar can attract lightening and because fiberglass is not an electrical conductor these metal strips provide a path for the current to flow to the rest of the airplane if lightening strikes the radar dome.