Analysis of Advanced Flight Management Systems (FMSs)

The differences in performance of various manufacturers' Flight Management Systems (FMSs) and the associated Flight Management Computers (FMCs) have the potential for significant impact on the air traffic control (ATC) system and as such need to be examined. While area navigation (RNAV) and required navigation performance (RNP) procedures and routes are designed according to criteria contained in Federal Aviation Administration (FAA) orders, FMC manufacturers build their systems in accordance with Minimum Aviation System Performance Standards (MASPS) and the Minimum Operational Performance Standards (MOPS) for area navigation systems, Technical Service Orders and Advisory Circulars. The expectation is the resulting performance of the aircraft FMC will meet the design requirements identified in the FAA criteria. The goal is procedures where aircraft operations result in repeatable and predictable paths. Sometimes, due to the disconnect between procedure design criteria and aircraft performance the paths of various aircraft on the same procedure do not overlap. Studies have shown that these differences are a result of variations in FMS equipment, variations and errors in data collection and processing, variations in pilot training and flight procedures and variations in aircraft performance. The hypothesis of this paper was that the basic FMCs built by the major manufacturers and installed as the core of the FMS in various airframe platforms would perform very near the same. This paper is a report of field observations made on five different manufacturer's test bench FMCs and the FAA's full-motion simulator in Oklahoma City. It focuses on lateral path (lateral navigation [LNAV]) as that is the major issue for air traffic controllers.