structural applications. The fiberglass molded mat is typically  used in combination with fiberglass fabric. The molded mats  are impregnated with resin just like a wet layup for fiberglass  fabric. The advantage of the molded mat is the lower cost  and the ease of use. strike. It is important that these lightning protection strips are  in good condition to avoid damage to the radome structure.  Typical failures of lightning protection strips that are found  during inspection are high resistance caused by shorts in the  strips or attaching hardware and disbonding of the strips from  the radome surface.  [Figures 7-69] Aircraft radomes, being an electronic window for the radar,  are often made of nonconducting honeycomb sandwich  structure with only three or four plies of fiberglass. The  skins are so thin so that they do not block the radar signals.  The thin structure, combined with the location in front of the  aircraft, makes the radome vulnerable to hail damage, bird  strikes, and lightning strikes. Low-impact damage could  lead to disbonds and delamination. Often, water is found in  the radome structure due to impact damage or erosion. The  moisture collects in the core material and begins a freeze- thaw cycle each time the airplane is flown. This eventually  breaks down the honeycomb material causing a soft spot on  the radome itself. Damage to a radome needs to be repaired  quickly to avoid further damage and radar signal obstructions.  Trapped water or moisture can produce a shadow on the radar  image and severely degrade the performance of the radar.  To detect water ingression in radomes, the available NDE  techniques include x-ray radiography, infrared thermography,  and a radome moisture meter that measures the RF power  loss caused by the presence of water. The repairs to radomes  are similar to repairs to other honeycomb structures, but the  technician needs to realize that repairs could affect the radar  performance. A special tool is necessary to repair severely  damaged radomes.  [Figure 7-68] Repairs to damaged composite structures can be made with an  external patch. The external patch repair could be made with  prepreg, a wet layup, or a precured patch. External patches  are usually stepped to reduce the stress concentration at the  edge of the patch. The disadvantages of the external patch are  the eccentricity of the loading that causes peel stresses and  the protrusion of the patch in the air stream. The advantage  of the external patch is that it is easier to accomplish than a  flush scarf-type repair. The repair methods for carbon, fiberglass, and Kevlar$^{®}$ are  similar. Fiberglass is sometimes used to repair Kevlar$^{®}$  material. The main steps in repairing damage with an external  patch are investigating and mapping the damage, removal  of the damage, layup of the repair plies, vacuum bagging,  curing, and finish coating. Trim out the damage to a smooth round or oval shape. Use  scotch or sand paper to rough up the parent surface at least  1 inch larger than the patch size. Clean the surface with an  approved solvent and cheese cloth. Transmissivity testing after radome repair ensures that the  radar signal is transmitted properly through the radome.  Radomes have lightning protections strips bonded to the  outside of the radome to dissipate the energy of a lighting  Use the SRM to determine the number, size, and orientation  of the repair plies. The repair ply material and orientation  must be the same as the orientation of the parent structure.  The repair can be stepped to reduce peel stresses at the edges. 7-41 Figure 7-69.  Lightning protection strips on a radome. Figure 7-68.  Radome repair tool. Step 3: Layup of the Repair Plies Step 2: Damage Removal Step 1: Investigating and Mapping the Damage External Bonded Repair With Prepreg Plies Use the tap test or ultrasonic test to map out the damage. External Bonded Patch Repairs Radome Repairs