Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFIED- 17- AC/243(Panel-8)TR/7Volume 2ce2.1 FUNCTION FLOW DIAGRAMSWhat the technique doesA function flow diagram identifies the sequential relationships of the functions required to perform the mission andoperations defined in the operational requirement and analysed in the mission analysis. Starting with the system ormission objectives and the mission analyses, function flows are developed at increasing levels of detail, down to thelevel where specific tasks can be identified for performance by hardware, software, or human operators. Typically theto analysis proceeds by successive decompositions of the individual functions. Examples are provided in sections 3.1.2and 3.2.3 of Volume 2, Part 2. These graphical representations arc the starting point for the determination of detailedsystem requirements.140 2.0 50pertorprfo perform performpre-f light turn-around maintenanceiis- -operations o e operations operations l*:N2. fh Ref.- tpe olpeeormdegraded flightoperations.0Rf-- No. rt0 Ret.RfperformperformY_ flight Adegradedflight- erations .. operationsflyto combat OR fly combat OR totu performarea x prtosbase turn-aroujnd |operationsFigure 2.2: First and second level function flow diagrams for a tactical fighter aircraftFunction Flow Diagrams (FFDs) are sometimes called Function Flow Block Diagrams. The term is confusing,because Function Block Diagrams are static representations of system functions grouped into organizational areas;Function Flow Diagrams indicate the sequential relationships of all the functions needed to accomplish the systemperformance requirements (US Defense Systems Management College, 1990). FFDs are constructed by arranging insequence all of the functions that are believed necessary to perform the mission, or to fulfil the system performancerequirements. The sequence is arranged to reflect the order in which the functions are performed. The flows areconstructed using "AND/OR" logic, to distinguish between functions conducted in series or parallel. Flowconnections normally enter a function box from the left, and exit from the righL "No go" connections can exit fromthe bottom of a function box. The individual functions are numbered using a system which indicates the order of theNATO UNCLASSIFIED- 17 - i