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

Human Factors Engineering (HFE) Issues 249
itself as areas of increased pressure or “hot spots,” can result in headaches
or general discomfort which distracts, degrading performance. The optical
adjustment factor represents the ability of the wearer to adjust the optics to
achieve full FOV. The last factor, stability, addresses the ability to
maintain the exit pupil(s). A displacement of the exit pupil(s), with the
accompanying reduced FOV, due to helmet slippage or transmitted
vibration reduces mission effectiveness. However, a deficiency of the
model is the failure to provide any numerical values for these factors.
Egress
In general, normal ingress and egress from the aircraft cabin is
becoming more of a challenge as we further encumber the aircrew and
shrink the entry access, as through the canopy doors of the AH-1 Cobra,
AH-64 Apache, and RAH-66 Comanche. Aviators first started doffing
equipment, e.g., NVGs on the SPH-4 in the cockpit seated position, to
avoid inadvertent release and damage during entry and exit. AH-64
aviators rarely enter or exit the cockpit wearing the IHADSS helmet,
primarily to prevent damage to the head tracking photosensors mounted on
the helmet. Once inside and secured, the helmet communication assembly
and video cables are plugged in, and the HDU can be attached; upon exit,
the HDU must be first removed. In the event of emergency egress, the
three attached cables are each provisioned with a hands-free release. If
mission scenarios dictate, the M-43 protective mask and blower assembly
also possess a separate hands-free release capability. The RAH-66
Comanche program is engineering a single-point release of all head
attached cables for emergency egress.
Equipment Compatibility
All HMD designs must be physically and functionally compatible with
all existing aviation life support and mission equipment. Examples include
corrective/protective eyewear, protective masks, oxygen masks, shoulder
harnesses, survival vests and flotation equipment and components, body
armor, aircraft seat armor, and cabin interior structures and systems. Figure
9.1 shows a frontal view of an Apache aviator wearing a full ALSE
ensemble with M-43 mask. Figure 9.2 shows the potential for interior
aircraft compatibility by, depicting an aviator in the Apache front seat with
the IHADSS HDU attached. Potential compatibility problem areas with the
Comanche HIDSS were found with body and seat armor, shoulder harness