The Local Area Augmentation System (LAAS) is a ground-based differential GPS system being developed to support aircraft precision approach and landing navigation
with guaranteed accuracy, integrity and continuity. Stanford University has designed, implemented and tested a LAAS Ground Facility (LGF) prototype, known as the Integrity Monitor Testbed (IMT). It is used to insure that the LGF meets its requirements for navigation integrity and continuity for Category I precision approach and to support future research for Category II/III operations. With support from the U.S Federal Aviation Administration (FAA), Stanford University has developed the Position Domain Monitor (PDM) algorithms and has implemented them in post-processing software on the IMT prototype platform. This paper describes in detail the PDM procedures and their roles in improving the LGF to meet integrity, availability and continuity requirements. The results of the most recent nominal and failure tests demonstrate that as an addition to the LGF architecture, PDM can provide the extra integrity in the event that the broadcast standard deviation of correction error (σ pr_gnd) is violated Further the addition of the PDM adds support to improve high availability.