Aerospace has established historical best practices for independent review teams, leading to the current operations policies and procedures of the Mission Assurance Team and the Independent Readiness Review Team. This approach is based on determination and evaluation of the main items believed to pose the greatest risk to space launch missions. A short, but powerful summary of these practices is below:
1. Test-Like-You-Fly Exceptions
One of the most important lessons in the space launch business is that hardware and software must be tested in the same manner that they will be flown. Exceptions to the test-like-you-fly approach have resulted in mission failures and represent an increased program risk that must be addressed.
2. Critical Qualification Margins
Hardware that has minimal safety margins poses an increased risk to failure because of variations in mechanical properties, performance, or other critical measures. It is important to check the qualification margins of critical items.
3. First-Flight Items
First-flight items receive increased scrutiny simply because they have not been demonstrated to work under actual flight conditions. The review team requests a list of first-flight items at each review along with a clear description of the qualification performed on them.
4. Single-Point Failures
Redundancy in a system significantly reduces the probability of failure. The manufacturing documentation of single-point failures must be carefully scrutinized to ensure an adequate level of quality.
5. Nonconformance
Hardware or software that does not meet specifications will be reworked or reevaluated for use "as is." Panel members review the actions taken to correct these nonconformances and assess them for adequacy. In some cases, independent review has shown that the contractor's justification for use "as is" was inadequate, resulting in the replacement of questionable hardware.
6. Anomalies
Anomalies represent situations where hardware or software did not perform as expected. Careful review and analysis is required to determine root cause and verify that the anomaly will not recur in flight or will not have a significant impact on the mission.
7. Escapes
Escapes represent events in which the contractor missed something, such as releasing hardware that did not receive all of the required testing. The review team strives to identify escapes as part of the pedigree review and hardware acceptance review. The Mission Assurance Team requests a list of contractor escapements as part of the review "inbrief." Once identified, escapes are carefully reviewed to assess the likely impact on mission performance, and recommendations are made for corrective action. This may include test or analysis or simply use as is.
8. Unverified Failures
Unverified failures are those in which the root cause is not identified. Without a root cause, it is hard to know what to fix, nor can there be assurance that the failure will not occur in flight. In these cases, fishbone diagrams are created, which detail cause and effect relationships, and potential root causes and remedies.
9. Out-of-Position/Sequence Work
Occasionally, contractors will deviate from their paperwork and perform work out of sequence, or in a configuration different from the one that was used to build up the original assembly. This may result in assembly errors that need to be addressed or test results that need to be revalidated. The review team reviews these cases to evaluate their impact on the mission and to offer recommendations.
10. Out-of-Family Results
Out-of-family results are carefully reviewed because they often indicate that something has changed in the production process that may cause a reduction in performance. The use of statistical process control is an effective means to identify out-of-family results.