Re: ... the FAA's statutory mandate to "promote" the aviation industry
@Mephisto - Grandfathering works OK as long as the rules are followed. In-service safety data is worth much more than predicted or calculated safety performance and all new systems will, after a number of hours in service, have actual safety performance data which are more accurate than the original design calculations. I know which data set I'd rather rely on when I'm flying.
Of course, this only goes for elements of the system which can truly be grandfathered - i.e. the config. and function in the system is unchanged from its parent's and can be isolated from any new elements of the design. It's getting much more difficult as more systems move into, or depend on, software to carry out functions which once were, essentially, black-box hardware solutions and much easier to make a grandfathering case for.
Having worked on safety-critical systems I'm familiar with the attempts made by designers, suppliers and operators to persuade regulators that grandfathering can be extended beyond reasonable boundaries because it can save a shedload of money in throughout the project lifecycle from design through V&V and even into maintenance/support. . What's needed is a strong regulator and I fear that this might be part of the problem in the 737 case.