Never make the same mistake twice-using configuration control and error analysis to improve software quality

To provide a controlled environment, changes to the Space Shuttle primary avionics system software (PASS) are grouped into operational increments (OIs) that identify a predefined set of changes and discrepancy corrections (a baseline) for that OI. Descriptions of the PASS development and verification process, the quality programs and causal analysis, and the process changes are given. Two early processes implemented were an automated configuration management database and a prologue in all the code modules. This allows a causal analysis program which permits each problem to be analyzed to determine the change authorization that caused the code modification that results in the problem. This causal analysis provides the information that is used for process improvement and to measure effectiveness