Use of Flight Symbology on a Head-Worn Display During Approach and Landing: Does Monocular Symbology Require Attentional Resources?

The approach and landing phase of flight is among the most safety-critical operations in civil aviation, particularly when outward visibility is limited by weather. To mitigate risks of this operation, pilots fly with a Head-Up Display (HUD), which presents flight symbology on a transparent screen at a focal distance of optical infinity so that the pilot can view primary flight information while maintaining visual contact with the runway. The Head-Worn Display (HWD) is an emerging technology in civil aviation that is designed to provide the benefits of a HUD; however, it features unique optical characteristics that may impact pilots’ performance and workload while they fly. HWDs can be binocular (i.e., displaying symbology to both eyes) or monocular (i.e., displaying symbology to a single eye). HWDs may also present symbology at a focal distance nearer than optical infinity. When flying with a monocular HWD, binocular rivalry occurs, which may impact the pilot’s ability to use the symbology and may impose demands on the pilot’s attention. This raises questions about whether flying with a monocular HWD impacts pilots’ flying performance, elevates workload, and negatively impacts divided attention and attention switching. Pilot performance and workload may also be impacted if the focal distance of the HWD symbology is nearer than optical infinity. To address these concerns, a study was carried out in which 48 Airline Transport Pilot (ATP) Captains flew approach and landing scenarios with varying visibility levels, some of which included abnormal events, in a Boeing 737 Level D-equivalent flight simulator while using flight symbology presented on a HUD, binocular HWD, and monocular HWD. Pilots rated their workload during each scenario using the NASA-TLX. The findings of the study suggest that the perceptual effects of binocular rivalry when flying with a monocular HWD may not impact the pilot’s ability to perform the primary task of the operation (i.e., maintain the flightpath of the approach, land on the runway centerline); however, pilots experienced elevated workload levels and were less able to perform the secondary task of the operation (i.e., monitor for and correct airspeed deviations). There were also impacts on pilot performance and responses to abnormal runway incursion events attributable to the optical characteristics of the HWD relative to those of the HUD, as well as monocular versus binocular configuration of the HWD. The findings from this research suggest that attentional resources are needed to combat the effects of binocular rivalry when flying with a monocular HWD, which in turn could elevate workload and compromise the ability to divide attention. Ultimately, this research contributes to the theoretical understanding of how visual attention is impacted by monocular viewing and provides practical takeaways for implementing a monocular or binocular HWD in lieu of a HUD during low-visibility approach and landing flight operations.