4.  5.  6. A process for adjusting stroke margin was developed, consisting of a shimming operation at the  stop feature for the lever. This allowed us to tune the latch release point to match SMA wire  stroke capability, so that acceptable stroke margin is achieved.  Lever retention spring force was tuned to a range, and controlled with a maximum. This ensured  adequate release force margins. Force margin is verified on each of unit as part of the production  process.  All field units with the dual lever return spring were recalled under a Technical Bulletin for  measurement of stroke and force margins. With some schedule impacts, all units which had been  built with dual springs were rebuilt and re-tested with the new stabilizing washer, process’  controls, and delivered with full margins for Flight use.  Discussion and Lessons Learned  The primary challenge of a release device is to maintain high performance margins for both pre-load  retention and operation. It is interesting that anomalies have been encountered in both these areas,  sequentially. The vibration anomaly focused attention on the preload retention aspect, and the analysis  showed that margins would be balanced with the dual spring. With the focus on improving vibration  performance, we added spring force and disturbed the release performance. Sometimes in an effort to  resolve one failure mode, we accidentally introduce another one. This is especially true when failure  investigations are performed under tremendous schedule pressure. In our case, the dual spring solution  was tested with greater than 400 life cycles prior to implementing the change, but the test unit had  positive stroke margin. Though the test unit passed, a variation in manufacturing process created a failure  of the revised design in a subsequent lot. The release anomaly is an example of unintended  consequences of a simple change, and insufficient controls on critical processes. The change to the  spring was necessary, and carefully implemented. But even with careful steps taken to validate the  change, there was an impact to mechanism performance.  When evaluating a qualified product, the variability of the production environment must be considered. It  is impractical and expensive to attempt qualification testing with all design tolerances at worst case.  However, worst case production results should be enveloped by the qualification program. In general, this  means that a production process control plan should be developed prior to qualification activities. A  qualified product must be manufactured with stable, controlled processes or future production lots will not  be similar to the original product.  Another lesson from this anomaly is that analysis of performance margins should always be verified by  actual measurement. Force and stroke margins on the QWKNUT were measured during development,  but not as part of the ongoing production process. The release anomaly led us to verify actual  performance margins, and ultimately these margin measurements were made a permanent part of the  production process. Stability of the performance margins over the product’s cycle life has also been  verified. The overall result is more robust hardware.  The investigation process was difficult and expensive, and impacted deliveries to several programs. It is  painful to have to recall flight hardware which has been delivered. However, the process has been  instrumental to the advancement of the design. We would not have discovered low SMA stroke and  variable performance margins had we not made the change to the dual spring. All 3 design generations  have been enhanced by the investigation of this anomaly.  Once the corrective actions were implemented, we proceeded to qualification of the “Gen 1 B design with  optimized design and manufacturing process.  Life-Test Pin Failure  Delta-Qualification of the Gen 1B design proceeded, using two test units which were rebuilt from the  failed lot in the release anomaly. The units passed all tests and proceeded into an extended life test, at  the end of which another failure was encountered. In each unit, one of the two spring posts (“flywheel  83