intermittent vibration behavior and the variability in release force measurements. If the toggle is on the  “flat” area of the lever, a tangential driving force results and leads to release of the device. If a toggle is  located on the curved surface of the lever, no driving force is present and no release occurs (Figure 4).  The width of the flats corresponds closely to the nominal location of toggle contact when the device is  latched. In this case, small variations in toggle position on the critical surface caused the variability in  latch performance. The physical cause was confirmed when the discrepant lever arm in the failed unit  was replaced with a conforming part from another lot, and the unit passed 3 repetitions of vibration  exposure (35 Grms, 3 minutes).  Root Cause  The root cause of the failure was found to be inadequate form control of the critical latch surface. Though  the latch surface was depicted on the drawing with a continuous curvature, the dimensional controls were  not adequate to ensure this. A total of 5 production lots of lever arms were received. The first 4 production  lots of parts met the design intent. The 51h lot was procured from a new supplier who used a different  machining process, which did not produce the intended surface at the critical latch point. The inspection  process did not detect the different geometry since the drawing did not specifically control the feature  shape. The inadequate drawing controls, combined with variation in manufacturing process (change of  vendor, machine, or even machinist) created the opportunity for the discrepancy. Fortunately, the  discrepant lot of levers was confined to the current production run, and no field units were affected.  Continuous curvature between 45” surfaces \  Burnish mal  indicating Tc  contact poin  Lever from previous GOOD lot - MoS,  coating intact; continuous curvature of  radius is evident “Flats  Burnisl  indicat  contac  Lever from discrepant lot - MoS,  stripped down to anodize  Figure 5. Lever Surface Discrepancy  Corrective Actions  The corrective actions for the vibration anomaly included adding proper engineering controls to the critical  lever surface to ensure design intent is met. The curved surface is now tightly controlled on the drawing  using runout and true position callouts. 100% inspection of this surface is required per an inspection  process defined on the drawing, followed by engineering review before parts are certified and released.  Process controls were also added at the assembly level to verify proper latch performance. These include  measurement of retention spring force and force required to release the latch and defined pass/fail criteria  (Figure 6). The latch release point is also screened against pass/fail criteria. The dual-spring design  change was implemented (and delta-qualification tested) to improve margins for vibration performance,  and prevent handling damage. Finally, acceptance level vibration testing under nominal preload is  performed on all units.  Once the lever surface was restored to the intended geometry, the device has proven to be extremely  robust with respect to vibration exposure. Delta qualification tests were performed at greater than 42  Grms with the lever arms intentionally shimmed 0.508 mm (0.020 in.) in the direction of release (to  approximately 70% of the release point) and all units passed the test.  79