liner that is form-fit and constructed from one- ply fiberglass backing (contour-molded to fit within the PRK-37/P helmet shell), a leather covering, and a comfort pad. The leather covering and comfort pad are cemented to the fiberglass backing. The fiberglass backing has two holes for introduction of foam chemicals. When properly fitted, the liner absorbs impact energy and makes the helmet stable and comfortable. The aircrew member wears a perspiration-absorbing cotton skull cap to extend the life of the liner. PRK-40/P HELMET SHELL LINER AS- SEMBLY. The PRK-40/P helmet shell liner, which comes in two sizes and consists of a premolded 1/2-inch thick polystyrene foam liner, is molded to fit inside the PRK-37/P helmet shell assembly. Final fitting of the PRK-40/P is accomplished by a series of different fitting pads. Also included in the assembly is a nape strap to allow a snugger fit. When properly fitted, the liner is designed to provide impact energy absorption, helmet stability, and comfort. EEK-4A/P HELMET VISOR, SINGLE LENS. The EEK-4A/P is a single lens helmet visor assembly. When installed on the helmet shell, it protects the face and eyes from impact, projectile penetration, sun glare, dust, windblast, and fire. Each assembly comes with inter- changeable clear and neutral lenses. PRU-36/P HELMET VISOR, DUAL LENS. The PRU-36/P is a dual lens helmet visor assembly, which provides the aircrew member with the same protection as the EEK-4A/P. EEK-3/P HELMET VISOR, DUAL LENS. The EEK-3/P is a dual lens helmet visor assembly, which gives the aircrew member the same protection as the EEK-4A/P. Each assembly comes with a neodymium laser protective inner lens and an interchangeable clear and neutral outer lens. R-1825/AVG-8, R-1826/AVG-8 HELMET VISORS. The R-1825/AVG-8 mounts on a large size helmet shell while model R-1826/AVG-8 mounts on a medium. The receiver includes a parabolic visor, which provides the pilot with a collimated reticle image. Two sensor elec- tronic assemblies, one mounted in each side of the receiver housing, assist in convert- ing the pilot’s line of sight into aircraft coordinates. The main assemblies of the receiver are the housing, the visor assembly, and the harness assembly. COMMUNICATION CABLE ASSEM- BLIES. Each of the helmet assemblies is outfitted with the appropriate communication components for operation with aircraft ICS (Intercommunica- tion System). M-87/AIC BOOM MICROPHONE AS- SEMBLY. The boom microphone assembly provides communication when the oxygen mask is not in use, as well as walkaround capabilities. NOTE: Detailed information on the fabrication of the form-fit liners can be found in the NAVAIR 13-1-6.7. SIZING THE PRK-37/P When building up the HGU pilots protective helmet, it is very important that you start with the proper size helmet shell (PRK-37/P). The PRK-37/P is available in four sizes, (medium, medium/large, large, X-large). To determine the proper size, you must first measure the circumference of the head, at the hatband line, with a tape measure. Once you have the correct measurement, you can determine the equivalent helmet size by referring to table 4-3. HELMET CONFIGURATION BUILDUP Once the basic PRK-37/P helmet shell and major components are received, carefully inspect the shipping containers for evidence of damage or signs of abuse. Open each container and verify that all the required items have been included. If any parts are defective, damaged, or missing, replace all items in the shipping container, prepare a Deficiency Investigation Report, and notify the proper authority. Once the helmet shell and related components have been accepted, the shell may be built up by adding or removing major components in order to obtain the desired configuration for required aircrew or aircraft application. Before you attempt to build up the helmet, it is necessary to follow the steps outlined in the NAVAIR 13-1-6.7 for each major component you are installing. MAINTENANCE As with all equipment that you work with and maintain, proper care of the fixed-wing series 4-21