SYSTEM MODIFICATIONS

Kossiakoff and Sweet (2003) discuss the effect of technological improvements and obsolescence of complex systems and how this results in an opportunity to improve the system by modifications, design changes or upgrades. These modifications, design changes, or retro-fits are undertaken to restore the overall system effectiveness by replacing subsystems and components at a fraction of the cost of the total system. Such a modification is referred to as a system upgrade. Military aircraft generally undergo upgrades or modifications during their operating life, with avionics, weapons systems and propulsion systems being popular subsystems to be replaced. In the civil aviation field, it is often economical and advantageous to replace obsolete avionics or passenger entertainment systems as an upgrade program.

2.2.1 Modification lifecycle

Kossiakoff and Sweet (2003) state that the development, manufacture and installation of a system upgrade or modification can be considered to have a systems development life-cycle of its own, with phases like, or the same as those of the main life-cycle. In this case SE is also applicable to these upgrades and modifications.

In this context, the concept development stage described by Kossiakoff and Sweet (2003) begins with recognition of a need for a major capability improvement to

address mission or economic deficiencies in the current system. The concept exploration stage starts with a process which compares several options of upgrading a subsystem with a total replacement by a new or superior subsystem. Kossiakoff and Sweet (2003) indicate that a convincing need for a limited system upgrade or modification, will lead to a decision to proceed, and hence the next stage in concept development. This concept definition phase for a modification resembles a new system, except the scope of the system architecture and functional allocation is limited to certain subsystems or components. Proportionally greater effort is required to achieve compatibility with the unmodified subsystems or components, to ensure that the original functional and physical architecture is maintained. Therefore, these constraints require of high level of SE input to accommodate a variety of interfaces and interactions between the existing subsystems and the new subsystems.

Furthermore, this process must accomplish this with a minimum of redesign, whist assuring that performance and reliability attributes have not been compromised.

Similarly, the engineering development stage is limited to the new components that are to be introduced to the system under modification or upgrade. The integration of the modified system faces other challenges beyond those normally associated with a new system, which is related to two main factors as described by Kossiakoff and Sweet (2003). Firstly, the system being modified is more than likely been subject of numerous repairs as a result of a number of years of operation. During this time these repairs may have not been adequately documented or poorly configuration-managed.

Furthermore, in the case of a fleet of systems some may have been subject to different repairs or no repairs at all, making the fleet increasingly different over a period. This system configuration uncertainty requires extensive audits or diagnostic testing case of software and adaption during the modification process.

Kossiakoff and Sweet (2003) state that the level and scope of subsystem test and evaluation required after a major upgrade or modification can range considerably from an evaluation limited to the new capabilities provided, to a full repeat of the original system evaluation and certification efforts. The level of test and evaluation effort is determined by the degree that the modifications affect the system capabilities that can be verified separately. Alternatively, when the modification alters the central or core functions of the system, it is necessary to perform an extensive re-evaluation of the total system. This may mean that an extensive re-certification program be required.

Lastly Kossiakoff and Sweet (2003) state that major system modifications always require correspondingly major changes in logistic support, particularly in those areas of spare parts inventory, publications updates and training. These latter stages of the design life-cycle require the same SE guidance as associated with the development of the original system. While the scope of the systems engineering effort is less, the criticality of design decisions and management of their impacts is no less important.

Faulconbridge and Ryan (2014) also discuss the impact of modifications to a system that has seen operational service or use – with this in this context being referred to as the Utilisation phase. The major activities during this phase include system operational use, system life-cycle support and modifications (or sometimes referred to as system Upgrade by Kossiakoff and Sweet (2003). Configuration management plays an important role during the utilisation phase to ensure that the configuration is managed, maintained and updated as required. Differences in physical configuration and the system documentation can make maintenance and operation potentially difficult and dangerous, particularly when a fleet of systems is involved.

Faulconbridge and Ryan (2014) state that modifications may be required to rectify deficiencies with the performance of the system that were not identified during the acquisition phase. These deficiencies may be identified during the Operational Test &

Evaluation (OT&E) phase or later operational use, where the system is placed in its operational environment and used by operational personnel. Other reasons for modifications may be a result of susceptibility to failure as part of the Failure Reporting Analysis and Corrective Action System (FRACAS), and that engineering changes are required via a modification to correct failures or system unreliability.

Modifications may be undertaken to changing system level requirements caused by a range of factors including operational support (technology obsolescence) and sustainability issues, or environmental factors. The latter may be the phasing-in or enforcement of new environmental controls or regulations impacting the operations of these systems. As stated by Faulconbridge and Ryan (2014) there may be opportunities to increase efficiency of the system, reduce weight, or to reduce costs, through the replacement of system elements with improved designs. Given these reasons, depending on the modification size and scope, there is a potential to significantly impact system performance and functionality. As shown in Figure 8, significant

modifications can be considered as a systems development activity, and that SE methodologies may be employed to achieve modifications.

Figure 8. System modification impacts in the utilisation phase

Faulconbridge and Ryan (2014)

2.2.2 Cost of changes

Faulconbridge and Ryan (2014) state that the principal causes of cost and schedule overruns on large scale complex systems engineering development projects can be traced to various factors. These factors could include overambitious promotion of the modification, selection of low Technology Readiness Level (TRL) technology, lack of corporate strategic guidance, requirements instability or uncertainty, unrealistic project baselines, inexperienced project staff, and more generally inadequate SE.

Faulconbridge and Ryan (2014) account for SE costs through implementation of systems processes and methodologies. These cost and schedule difficulties are often a result of inadequate requirements engineering practices, where poor requirements cannot be rectified by design. Faulconbridge and Ryan (2014) indicate that the SE has its greatest impact through structured application of these processes during the earliest phases of the project where changes can be affected easily and modification cost is the lowest. Consequently, SE provides the ideal opportunity to have the greatest impact on a project at time when these changes are easiest and inexpensive to make. There is therefore a strong incentive to manage and control these early phase conceptual design processes.

2.3 SUSTAINABILITY IN CONCEPTUAL DESIGN