Requirements

In my earlier post on the Valukas report about GM's ignition switch problems I questioned whether there was much difference between waiving a requirement and changing it.  Upon reflection I think this is wrong.  It is better to weaken a requirement if necessary than to waive it.  The problem with waiving a requirement is then you are left with nothing.  So the supplier no longer has any incentive to pay attention to that characteristic and performance may continue to deteriorate as the design is finalized and the part moves into production.   Also quality control problems which mean that some parts perform very badly may not get picked if that aspect of performance is not being measured.  The Valukas report didn't discuss how much the ignition switches varied, perhaps most of the problems were from switches with exceptionally bad performance.  Of course specifications ideally provide a safety margin so that even below average parts still perform satisfactorily.

Another advantage to not allowing a complete waiver is it might have caused the GM engineer to focus on the fact that there was a point where reduced effort to operate the switch becomes completely unacceptable.  In the process of determining where that point was he might have realized the switch was getting uncomfortably close.