Operational and Functional Requirements for the Navigation System in Terminal Areas

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Operational and Functional Requirements for the Navigation System in Terminal Areas

S. C. Mohleji

A comprehensive set of operational requirements relating the capabilities of the navigation system and its use in the ATC environment are developed in this paper by modifying the operational requirements for MLS established by the International Civil Aviation Organization. In order to establish the functional requirements, an interrelationship is established between the navigation system parameters, route geometry and ATC procedures considering system uncertainties. An impact of each ATC uncertainty (navigation, surveillance, communication delays, airspeeds and winds) is first examined individually by computing the time dispersions between the planned vs. the achieved aircraft performance. Then a total dispersion and control interaction is established by calculating the time variability due to speed adjustments permitted under ATC procedures, and by statistically combining the impact of the ATC uncertainties using a root sum square (RSS) approach. This technique is general enough to permit evaluation of functional requirements (accuracy, coverage and channel capacity) of any navigation system under varying ATC parameters, procedures and operational requirements. Several navigation scenarios are evaluated based on the existing and future capabilities of the navigation systems. These include: (1) existing VOR/DME systems with airline quality avionics; (2) existing, VOR/DME system with a + or - 40 deg MLS providing guidance within the coverage; and (3) a highly accurate navaid such as DAS (DME/Azimuth system) proposed by the Federal Republic of Germany.