Barber, S., Schwab, D., and Zimmerman, K., "Head Up and Eyes Out Enabling Equivalent Visual Operations with the Head Up Display," SAE Int. J. Aerosp. 6(1):237-246, 2013, doi:10.4271/2013-01-2300.
Following the introduction of Head-Up Displays (HUD) into commercial airplanes over 30 years ago, many aircraft manufacturers are now installing HUDs as baseline or as a selectable option on their latest designs. Most pilots that have used the HUD in difficult flying conditions prefer it to classic flight deck configurations with head-down displays only.This paper describes the features and benefits of the HUD that allow the pilot to remain head-up and eyes-out throughout the flight, especially in the crowded skies around an airport. This is achievable because the HUD provides all the primary flight information needed to fly the airplane. Some of the information is conformal to the outside world and the whole image is focused at optical infinity, eliminating the need for the pilot to refocus between the HUD symbology and real world features viewed through the HUD.Flight path based flying is intuitive, reducing workload and improving safety by allowing the pilot to maintain better situational awareness of the airplane's energy state. Use of HUD symbology enables increased flight and navigational accuracy to be achieved. Additionally, the HUD provides an advanced monitoring capability for the pilot while the airplane is in automated flight, and allows him/her to independently monitor the control loop, even when not in physical control of the airplane.This paper also discusses the capabilities of the Head-Up Guidance System (HGS™) as related to low visibility operations. Where these operations have been conducted traditionally with automatic guidance systems, the HGS provides the opportunity for pilots to manually conduct the approach, landing and rollout in visibilities as low as 600RVR and takeoffs to 300RVR. Several regulatory “Special Authorizations” have been developed to specifically take advantage of the HUD's low visibility capabilities, to allow increased operational flexibility.The Federal Aviation Administration (FAA) Next Generation Air Transportation System will provide opportunities for Equivalent Visual Operations, which may allow VFR operational tempos, and potentially VFR procedures, to be maintained under low visibility conditions. Vision System technologies, already available on some airplanes, allow HUD symbology to be underlaid with a conformal view of terrain features ahead of the airplane. These technologies, supported by NASA research, allow for the integration of sensor-based Enhanced Vision, Synthetic Vision, and Combined Vision imagery for use both in the air and on the ground.An RTCA committee is defining performance standards for such Vision System technologies. These range from the use of Synthetic Vision, to achieve lower operational minima and increased situational awareness, to the use of sensor-based Enhanced Vision for approach, landing and taxi in visibilities as low as 300RVR.Both analysis and simulator/flight demonstrations, some sponsored by the FAA and NASA, continue to substantiate and quantify the safety benefits that can be realized in flying head-up with a HUD. The results of these studies continue to justify claims that the use of the HUD improves a pilot's accuracy and consistency in performing flight operations, particularly in the terminal area, leading to increased flight safety.