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 HGU84/P series helmet (fig. 11-3) is
designated for used by all helicopter aircrew members.
constructed of a multilayer 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,
chin/nape strap. The helmet provides maximum face,
eye, ear and head protection and comfort when properly
fitted to the wearer. The HGU84/P helmet is available
in four sizes, (M, LG, XLG, XLG wide) and can also be
fitted with specialized features for aircraft or mission.
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
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
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.
Figure 11-3.HGU84/P series helmet.
Figure 11-4.Cutaway anti-g coverall.