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HUD With a Velocity (Flight-Path) Vector Reduces Lateral Error During Landing in Restricted Visibility

Abstract The operational community has assumed that using a head-up display (HUD) instead of conventional head-down displays will increase accuracy and safety during approach and landing. The putative mechanism for this increase in safety is that previously demonstrated improvements in lateral and vertical control of the aircraft in flight should carry over to the landing situation. Alternatively, it is possible that, during approach and landing, the HUD might affect the pilot's ability to assimilate outside cues at the decision height, thereby reducing the success ratio for landings using an HUD. This article reports a pair of experiments that test these competing hypotheses. Taking advantage of the opportunity when an air transport operator introduced HUD in an existing aircraft fleet, we were able to use a Boeing 737-700 full-motion simulator flown by commercial airline pilots. We explored the effects of (a) HUD use, (b) ambient visibility, and (c) length of approach lighting on the size and location of the touchdown footprint. We also explored the effects of HUD use on approach success ratio. HUD use reduced the width of the touchdown footprint in all tested visibility and lighting conditions, including visibility below the minimum allowed. HUD use had no effect on the length of the touchdown footprint. We could not detect any decrease in approach success rate for HUD approaches. Based on these empirical data, the minimum visibility for approaches using HUDs could be set lower than for approaches without an HUD.