Precision navigation, display, and avionics technologies have progressed to the point that a head-up primary flight display incorporating synthetic elements such as terrain and commanded flight path is a possibility in the near future. The goal of such a display is to increase situation awareness and reduce aircrew reliance on warning systems or automation to prevent controlled flight into terrain (CFIT) mishaps. The primary flight display-and primary focus of attention-in modern fighter aircraft is a head-up display (HUD). This is becoming true also for newer transports in the U.S. Air Force inventory. Some human factors issues associated with synthetic vision in a head-down display are different from those associated with a head-up synthetic vision display, especially when the displays are used as primary flight references. Among these issues are the use of color, ability to see through the display, symbology clutter, compatibility between head-up and head-down displays, and attentional factors. This paper reports the results of a study in which HUD-experienced pilots flew simulated complex precision approaches to landing in three visibility conditions, with and without synthetic terrain, using either pathway-in-the-sky symbology or more traditional military standard HUD symbology. Workload and situation awareness measures were collected to determine the relative workload associated with these conditions and if, as has been proposed elsewhere, flying a pathway-in-the-sky display is associated with "cognitive capture", or a decrease in situation awareness concerning things other than the pathway. It was hypothesized that including pathway and synthetic terrain in a head-up primary flight display would result in a conformal symbology set that naturally draws pilots' attention to external events. It was also hypothesized that workload could be reduced by allowing pilots to maintain spatial orientation via preattentive processes rather than relying on instruments requiring focal vision and active interpretation.

This study was conducted to determine the flight technical performance, workload, and situation awareness of pilots flying a low-level curved approach to an austere airfield. This lowlevel ingress was flown under simulated night IMC with occasional breakouts into VMC. A total of 13 USAF pilots participated in this study. The simulated flights were performed in AFRL's Transport Aircraft Cockpit (TRAC) flight simulator. The simulator was configured using a C-17 aeromodel, and the head-up display showed either conventional commercial symbology (baseline) or one of two synthetic vision pathway configurations with wire-fiame terrain. One of the synthetic vision configurations used rectangular pathway elements (pavers) and the other configuration used a square wire-frame tunnel. Speed and altitude information was provided either in the form of tapes or dials in all three configurations. A secondary task was introduced to test the displays under increased levels of workload. The secondary task involved authentication of a Sdigit code. In addition, the pilots had to deal with traffic targets to which they were alerted on the head-down display. The flight technical data clearly indicated that both pathway formats @aver and tunnel) are superior to the baseline symbology format. For all practical purposes the paver and tunnel formats performed equally well. Head-up guidance with terrain and pathway information provided much tighter flight technical performance than conventional head-up guidance. Thus, we conclude that the mission capability of the potential military users could be substantially increased.

Results from previous studies (St. John & Risser, 2007, 2009) indicate the addition of a simple cognitive secondary task may mitigate vigilance decrements for a sustained attention task involving target acquisition. The effectiveness of the cognitive task increased when its onset was triggered by physiological indicators of inattention. The current study examined the generalizability of this methodology with a few modifications. A no intervention condition was added to provide a baseline and a short perceptual vigilance task (AVT) was added to examine the construct validity of the experimental task (ET). Finally, instead of using physiological indicators to trigger the intervention, a schedule was used that resembled that of the physiological intervention. Although vigilance decrements were observed for both the AVT and ET, only a weak relationship was observed between the two tasks. ET performance was not affected by the cognitive intervention. The weak relationship between the AVT and ET scores suggests that they are not measuring the same constructs. Further, the failure to replicate previous findings casts doubts on the robustness of the cognitive intervention for mitigating performance decrements on real-world tasks, especially when its onset is not linked with physiological indicators of inattention.

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