A Local Area Augmentation System (LAAS) architecture alternative has been developed to provide satellite navigation performance compliant with the stringent requirements for aircraft precision approach and landing. Code and carrier phase measurements from ground-based airport pseudolites (APLs), located at each end of the approach runway, are optimally processed at the aircraft to improve vertical performance and thus increase navigation availability. In addition, a new integrity monitoring architecture is introduced to provide the tightest achievable protection limits with respect to LAAS reference receiver failures. To demonstrate that the notional LAAS architecture is realizable, a prototype system was implemented at Moffett Federal Airfield in California for flight testing on a NASA Beechcraft King Air. In this paper, the ground and air components of the prototype architecture implementation are described. The real-time experimental results from King Air flight trials performed in September 1997 show exceptional navigation performance with the APL architecture, including a 95% vertical navigation error of 0.46 m.