NASA Procedures and Guidelines
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NPR 8621.1 Eff. Date: June 02, 2000 Cancellation Date: February 11, 2004	NASA Procedures and Guidelines for Mishap Reporting, Investigating, and Recordkeeping
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1.1 Method

1.1.1 Using the existing known system as a baseline, the investigator should examine the nature of all contemplated or real changes, and analyze the probable effect of each change (singly) and all changes (collectively) upon system risks. The process often requires the use of a walk-down, the method of physically examining the system or facility to identify the current configuration.

1.1.2 Alternatively, a change analysis could be initiated on an existing facility by comparing "as designed" with the "as built" configurations. In order to accomplish this, there would first be the need to physically identify the differences from the "as designed" configuration.

1.1.3 In either case, an exhaustive evaluation of the modifications or changes would be made and tabulated. Then the likely worst-case effects of each of those changes from the baseline are postulated. Finally, the combined effects are developed, the change in risk developed, and the overall results are reported. The process is graphically shown in Figure I-3.4-1 below.
 

1. Identify the system baseline                                                                             2. Identify changes - Walk-down                                                                             3. Examine each baseline change by postulating effects                                                                             4. Postulate collective/interactive effects                                                                             5. Conclude system risk or deviation from baseline risk                                                                             6. Report findings

1.1.4 Although originally conceived for management system applications, change analysis has come to be applied to systems of all kinds. It can only be applied, of course, if system design change or actual alteration has occurred or is contemplated. It is well applied as a means of optimizing the selection of a preferred change from among several candidate changes, or in aiding the design of a needed change. The technique can be applied meaningfully only to a system for which baseline risk has been established (e.g., as a result of prior analysis).

1.2 Thoroughness

Thoroughness is constrained only by the depth/detail in performing the analysis. Thoroughness required to analyze a given change is governed by the extent of the change itself. Effectiveness cannot exceed that of prior analyses used in establishing the baseline risk. Understanding of the physical principles governing the behavior of the system being changed is essential, in order that the effects of the change can be determined with confidence adequate to the purposes of the analysis. Assuming that the complexity of the changes does not appreciably exceed that of the system prior to alteration, mastery of the baseline analytical technique becomes sufficient.

1.3 Comments
Difficulty is determined largely by the extent to which the system had undergone (or will undergo) change, in combination with system baseline complexity. Identification of any existing configuration management documentation may reduce the time and effort involved with the change analysis process. The chief advantage of the technique lies in its "shortcut" approach, i.e., only the effects of changes need be analyzed, rather than the system as a whole. In this advantage also lies the technique's chief shortcoming, i.e., the presumption that the baseline analyses have been carried out adequately.

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