Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFIEDAC/243(Panel 8)TR/7- 18 -Volume 2functions, and the level of the analysis. Each diagram should include a reference block showing the next higher levelof analysis.Inputs to the techniqueThe analyst needs information on the mission sequence.derived from a mission analysis, or equivalent data on thesequence of events and operational requirements. Theanalyst also needs knowledge of previous, similar systemsand similar operational requirements.Outputs of the techniqueFunction flow diagrams provide a comprehensiveinventory of system functions that must be considered inassuring the ability to perform a mission. As moredetailed function flows are produced. specific systemrequirements begin to emerge. The diagrams provide aview of how the system will operate, in logical terms.When to useThe analysis should be conducted early in concept definition and design definition. The analysis should follow fromthe mission analyses; it precedes Function Allocation (3.3). Some texts treat FFDs as preceding the use ofRequirements Allocation Sheets (US Defense Systems Management College, 1990; USAF, 197 1.b).Related techniquesThe technique is related to the function analyses conducted as part of the system engineering effort (Lurcott, 1977).There is little reason why a common analysis is not conducted to serve all systems engineering analyses. Usually,however, the analyses conducted for other systems engineering specialities do not make the functions performed bythe system operators and maintainers explicit at the lower ievels of analysis. The technique is strongly related tosystems engineering techniques such as Sequence and Timing (SAT) diagrams (2.2) and to software requirementsdevelopment methods such as SADTr/1DEF® (2.3).ResourcesRequiredBecause of the need to reference functions across and between levels, and because of the iterative nature of theirdevelopment, it is desirable to have a computer system available that can create the function flow diagrams and keeptrack of the function names and reference numbers.Relative contributionUsers' reports vary from "medium" to "excellent". This technique is generally seen to make an importantcontribution to the identification of the functions that human operators will perform.ApplicationsThe technique has been widely used (see Laughery & Laughery, 1987: Nice, 1984), and has been employed in a widevariety of systems development projects. It has been used to analyse aircraft (both fixed and rotary wing). ship-boardsystems (combat systems, helicopter landing control systems, re-supply at sea systems), and land-based systems,including major command and control systems.NATO UNCLASSIFIED- 18 -