RANGING SOURCE FAULT INTEGRITY CONCEPTS FOR A LOCAL AIRPORT MONITOR FOR WAAS

This paper illustrates two concepts for analyzing the integrity of a local airport monitor (LAM) when dealing with ranging source (satellite) faults. The LAM performs local monitoring of the FAA's Wide Area Augmentation System (WAAS) to provide precision approach service to aircraft equipped with the Local Area Augmentation System (LAAS). In the first analysis the previously developed concept of a maximum allowable error in range (MERR) is revised to take advantage of the conservative protection level computed in the aircraft for the LAM position monitoring on the ground. The new proposed value of MERR provides adequate integrity for ranging source faults that might be mitigated outside the LAM (i.e., by WAAS itself) for a wide range of fault monitor operating parameters. This analysis is intended to provide a MERR for use in assessing performance of the WAAS signal quality monitor. The second analysis assesses ranging source fault risk mitigation (without an intermediate MERR) as would be provided by the LAM position monitor function. When applied to excessive acceleration ranging source faults, the analysis shows that adequate risk mitigation is provided by the LAM position monitor regardless of the size of faults due to steps, ramps or accelerations.