For over four decades the Head Up Display (HUD) has been a critical instrument in tactical aircraft, as well as in an increasing number of commercial air transports. HUDs provide a unique means to present vital information to the pilot, precisely overlaid on the real world, without the need to look down or refocus onto the instrument panel displays. HUD imaging technology, using high brightness CRTs, has remained largely unchanged during this period, despite dramatic advances in display technology across the remainder of the avionics spectrum. As reliability improvements have reduced life cycle costs for other avionics systems, the relative cost of ownership for CRT-based HUDs has become increasingly unacceptable. Further, as special-purpose CRTs have steadily been replaced by digital display alternatives the number of potential sources has dwindled, raising growing parts obsolescence issues. These issues can be resolved by replacing the CRT and its associated electronics with a solid-state digital image engine. Such "digital" HUDs (DHUDs) have been certified for use in a number of commercial air transports, and are gaining wide acceptance in the user community. The operational and environmental requirements for DHUDs for tactical aircraft are more demanding than for transports, however the core technologies are in place to meet these needs. The stage is set to achieve excellent performance, dramatic life cycle cost reductions and low cost, for both legacy and new tactical aircraft. This paper describes digital HUD development efforts to date and summarizes key performance parameters and design issues.
