Abstract
Abstract : The Thales Avionics Topowl(trade mark) Helmet Mounted Sight and Display System (HMSD) with and without the Communications Earplug (CEP) was tested for sound attenuation using American National Standards Institute (ANSI) standard S12.6-1984 and S12.6-1997 (R2002). Insertion loss measurements were made for the HMSD without the CEP in accordance with ANSI S12.42-1995 (R1999). The Thales Avionics Topowl(trade name) HMSD worn without the CEP does not meet the Navy/Marine Corps sound attenuation requirement but exceeds the requirement when worn with the CEP. When worn without the additional hearing protection afforded by the Communications Earplug or other passive earplugs, aircrew wearing the Thales Avionics Topowl(trade name) HMSD would be at risk due to higher noise exposure and reduced speech intelligibility, hence reduced operational capabilities. Expandable-forin or preformed earplugs could be employed with the Thales Avionics Topowl(trade name) HMSD to meet the Navy/Marine Corps hearing protection requirements. However, these types of earplugs will compromise speech intelligibility and, thus, negatively impact crew performance. The U.S. Army Aeromedical Research Laboratory recommends that Thales Avionics Topowl(trade name) HMSD not be used without the additional hearing protection and enhanced communications afforded by insert hearing protection and communication devices such as the CEP.
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