Head-up displays (HUDs) have become an integral part of the fighter aircraft and are now becoming increasingly popular in various nonmilitary sectors also. It enhances the pilot's performance by providing him with all of the flight, aircraft, target, and weapon data in collimated fashion superimposed on his forward view. The collimation of HUD symbology and infrared raster image removes requirement of refocusing eyes on outside events. However, there are attention capture and cognitive tunneling issues related with usage of HUD in aircraft. In this paper, effect of obstruction due to beam combiner frame in form of misaccommodation, misconvergence, and limited horizontal field of view (FOV) on attention capture of aircraft pilot has been presented. While the beam combiner frame is necessary to hold wavelength selective glasses, they provide obscuration in forward view of pilot in both, total field of view (TFOV) as well as instantaneous field of view (IFOV). Angle of combiner frame structure and its width present different degrees of obscuration to the pilot within the head motion box (HMB). These limitations cause inappropriate distribution of pilot's attention on outside events and aircraft events, as he has to adjust his head position to view the obscured part of outside world. This forces him to focus his attention more on outside events which may make him miss some event on HUD symbology. The study and experimental results have been presented in detail to corroborate this fact.
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