helmets  have  specialized  features,  such  as  the  Visual Target   Acquisition   System   (VTAS),   Night   Vision Goggle   (NVG)   assemblies,   laser   protective   lenses, sonar operator binaural cables, and boom microphones. The    HGU–84/P    series    helmet    (fig.    11-3)    is designated for used by all helicopter aircrew members. Helmet assemblies feature a lightweight shell constructed    of    a    multi–layer    mixed    composite    of graphite fabric and ballistic nylon fabric, an inner foam liner, three integrated visor assemblies (Neutral, Clear, and  Laser  Eye  Protective),  communication  cord  set, boom microphone, earphones, and a integrated chin/nape  strap.  The  helmet  provides  maximum  face, eye, ear and head protection and comfort when properly fitted to the wearer. The HGU–84/P helmet is available in four sizes, (M, LG, XLG, XLG wide) and can also be fitted with specialized features for aircraft or mission. ANTI-G COVERALLS When in flight, the body can have trouble adjusting to  stresses  produced  by  rapid  changing  of  speed  or direction. In situations such as seat ejection, ditching, or parachute opening shock, the short duration of the excessive force has little effect on the body. However, changing the direction of flight produces stress forces equal  to  several  times  the  normal  pull  of  gravity  for much  longer  periods  of  time.  These  longer  duration forces can have dangerous effects. At    5    g's    (5    times    the    force    of    gravity),    the aircrewman's body is exposed to a force that increases its  weight  5  times.  This  increased  weight  has  many effects. Your body is pushed down into your seat. Your arms and legs feel like lead, and operation of equipment becomes   more   difficult.   The   extra   weight   on   your internal  organs  causes  stomach  and  chest  pain.  Most important,  however,  is  the  effect  on  your  circulatory system. At 5 g's, your heart cannot pump enough blood to your   head.   When   this   happens,   you   will   pass   out. Wearing  anti-g  coveralls  will  help  prevent  this  from happening. The   Navy   uses   two   models   of   anti-g   coveralls (commonly called "G" suits). These coveralls provide protection   against   blacking   out,   loss   of   vision,   and lowered   mental   efficiency   caused   by   high   g-forces experienced in high-performance aircraft. Figure 11-4 shows a typical anti-g coverall. Anti-g coveralls compress your legs and stomach to prevent  blood  from  pooling  in  your  lower  body.  This increases  your  stress  tolerance  an  average  of  about  2 g's.  Without  an  anti-g  coverall,  you  may  be  able  to withstand about 4.5 to 5.5 g's without losing vision or blacking out. With a coverall, you can withstand 6.0 to 7.0 g's. This protection is available only for sustained accelerations of 4 to 5 seconds. Anti-g equipment does not offer protection in snap maneuvers where 10 to 12 g's are applied in about 1 second. Such extreme forces for a short time are not as harmful to the body as are lesser forces sustained for a longer time. 11-3 ANf1103 Figure 11-3.—HGU–84/P series helmet. ANf1104 Figure 11-4.—Cutaway anti-g coverall.