The research documented in this thesis is based on case studies focusing on three major USAF aircraft programs in the electronics sector. All three programs, designated as Programs A, B, and C for the purposes of this thesis, are the responsibility of a single System Program Office (SPO). Data on 118 engineering changes 7 were collected from contractor-submitted Class I Engineering Change Proposals (ECPs) archived at the SPO. In addition, supporting documents
pertaining to the three programs, as well as to the specific systems and subsystems within each of the three programs, were collected in order to assist in developing a comprehensive understanding of these engineering changes. Finally, 54 engineers and managers from prime contractors and the
program offices were interviewed to obtain their perspectives on the programs and the engineering changes. The causes and impacts of specific engineering changes were determined through a detailed examination of the data from these sources. Finally, broader interpretations and conclusions were drawn from the collected database.
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Past studies on engineering changes have focused on products other than defense aerospace products, and have concentrated primarily on the design-manufacturing interface within single
companies. Thus, engineering changes in the context of US defense aerospace product development - where the user community, the acquisition community, and the contractors share the responsibility for developing a product - remain largely unexplored. This research focused on three defense aircraft acquisition program case studies, referred to hereafter as Programs A, B, and C. The primary goal of these studies was to develop a better understanding of the causes and impacts of Class I engineering changes in the US defense aerospace product development context. Class I engineering changes, simply referred to as engineering changes below, are those that fundamentally modify the form, fit, and/or function of a product such that the results before and after the engineering changes are different, and are visible to all communities involved with developing the product. In addition, this research sought to identify ways in which contractors and customers may help to reduce the number of undesirable engineering changes.
For the three case-study programs, requirements definition issues, changes in user needs, the need to fix deficiencies, and technological changes were found to be the four dominant causes of engineering changes. It was also found that program characteristics determined the dominant causes in each of the programs. Engineering changes due to the four dominant causes across the three case-study programs were found to be most likely of high-impact. The scope of impact of engineering changes remained relatively constant with respect to time, and engineering changes rarely led to subsequent, unanticipated engineering changes. Thorough requirements definition facilitated by the use of integrated product teams (IPTs), prioritization on program schedule, and the use of mature technologies combined to allow Program C to make frequent engineering changes to accommodate evolving user needs and changes in technology without any program schedule delay. It was also found that had IPTs been used during the development phases of Programs A and B, the prime contractors and their suppliers might have been able to avoid some engineering changes.