ABSTRACTPrior to the adoption of the Wide‐Area Augmentation System (WAAS) as the primary radionavigation system for the future, a number of different augmentation techniques for providing enhanced integrity and availability of GPS for use in the National Airspace System were analyzed. This paper examines the availability of Loran‐C augmented GPS with receiver autonomous integrity monitoring (RAIM) for use in nonprecision approach. Availability of the augmented system is calculated at approximately 2300 airports over the continental United States. It is demonstrated that GPS availability is significantly enhanced with Loran‐C and barometric altimeter augmentation. The percentage of time augmented GPS is unavailable for nonprecision approach is reduced by at least two orders of magnitude relative to nonaugmented GPS. Loran‐C is by itself an approved supplemental nonprecision approach landing system that can function as a stand‐alone backup if GPS is degraded or unavailable. It is demonstrated that the augmented system represents an improved, redundant, and generally more robust supplemental navigation system; however, the Loran‐C augmented system cannot satisfy the requirements for a primary naviga