Demonstration of a procedure-based approach to functional analysis for an optionally piloted vehicle

In this publication, we present the process of functional analysis for the development of an Optionally Piloted Vehicle (OPV). The OPV is based on an existing CS-23-category general aviation aircraft and offers three modes of operation: A conventional manned mode, an automated control mode with safety pilot on board, and a completely unmanned mode. In order to avoid errors that could lead to unintended system behavior and ultimately impact flight safety, a structured development process is required. Previous publications presented the derivation of a concept of operations that contains normal, abnormal and emergency OPV procedures, which are based on the aircraft operating manual of the considered airplane. While focusing on functions that are needed to convert the existing aircraft into an OPV, this concept of operations serves as primary source for the functional analysis. The procedures are used to systematically identify functions on varying levels: Context, aircraft, systems and sub-systems level. As part of the functional analysis, these functions may then be decomposed into subfunctions to achieve a common granularity level over all functions. Both methods, procedurebased function derivation and conventional functional decomposition, are combined to ensure requirements and functional traceability as well as transparency of the development process. For defining the functional breakdown structure and functional analysis itself, we adopt wellestablished systems engineering methodologies and aerospace standards. We further apply the concept of private and public functions, well-known from object-oriented programming, to promote modularity and to facilitate allocation of functions to a system. A function life cycle scheme is proposed as basis for the function design and development. It defines the possible states and state transitions of a function aiming to prevent inadvertent or erroneous activation of inappropriate functions in different flight phases. The overall approach is demonstrated using two example procedures, one for initial climb and one for handover of control between two remote pilots.