Helmet-Mounted Displays: - USAARL - The - U.S. Army

Biodynamics 213
down. The helmet may or may not reposition itself after the motion ceases.
This is dependent on the slippage magnitude and the resiliency of the fitting
system.
Compatibility
The original purpose of the HGU-56/P aviator's helmet was to improve
integration with night vision devices, protective masks, ballistic, laser and
nuclear flash blindness eye protection while providing improvements in the
communications system, hearing protection, fit, head retention, and impact
characteristics. The helmet comes in 4 sizes and uses the TPL system to
provide a comfortable fit. However, it has been found that none of the
helmet liner systems are compatible with NBC protective masks,
particularly the custom form liners, and more so when the required hood is
worn underneath the helmet.
In the beginning of the HGU-56/P helmet development, the protective
mask was designed similar to an oxygen mask with a face shield and
attached to the helmet with standard oxygen mask fasteners. However, an
acceptable mask seal was only obtained with positive pressure from a
battery powered blower, similar to the one used for the M43 protective
mask. This concept was dropped after considering the logistics and human
factors issues.
In the HGU-56/P helmet fitting study (Towns and McLean, 1995),
(Bruckart et al., 1993) compatibility with the M43 protective mask and
ANVIS was judged to be poor even with the larger acceptable sized
helmets. During the M45 Aircrew Protective Mask (ACPM) operation tests
(OT), the participants could not wear the ACPM with the HGU-56/P helmet
without severe discomfort after only a few minutes. A separate modified
TPL that was custom fitted for the mask with the helmet was used during
OT as a temporary solution. However, this approach was recommended by
the Test Working Integration Group (TWIG) for the M45 ACPM, and has
been accepted by PM ALSE. With two separate TPLs, and the Air Warrior
requirement to don a mask in flight, the pilot will have to: 1) remove the
helmet, 2) retrieve and don the mask, 3) remove and store the normal TPL,
4) retrieve and insert the second TPL for the mask, and 5) redon the helmet.
Operationally, we believe the pilots may remove components or spacing
that make up the helmet liner or a skull cap as used by the IHADSS, but we
do not believe they will take the time to retrieve, insert, and accurately
position another TPL into the helmet. When a mask is worn underneath the
helmet, part of the helmet liner will have to be removed. Otherwise, the