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Fighter index of thermal stress (FITS): guidance for hot-weather aircraft operations.

Operation of fighter and trainer aircraft at low altitude in hot weather often involves significant heat stress on aircrews. Guidance for control of this stress and its adverse consequences has not heretofore been available. The Fighter Index of Thermal Stress (FITS) was derived from the Wet Bulb Globe Temperature (WBGT) using recent in-flight data on cockpit environments and assuming a fixed contribution from solar heating. The FITS table is entered with ground dry bulb temperature and dewpoint temperature, and yields an estimate of cockpit thermal stress. Caution and Danger Zones are designated on the table, based upon typical aircrew clothing, metabolic rate, and physiological status. Appropriate protective measures are recommended, including awareness of heat stress, limitations on ground operations, allowance of adequate recovery intervals, provision for fluid intake, and cancellation of flights under severe conditions. Possible applications of FITS are discussed together with its potential impact on flight operations at 30 USAF bases.