Frangible I agree with your analysis, changes to checklists and procedures meant to ameliorate design deficiencies belong to the short term during the period when redesign and implementation should take place, they are not a long term panacea. I wonder if Boeing's stubborn refusal to change the pressurization warning system on the 737 might have its roots in type certification issues and/or the potential for increased liability exposure on older models, absent an expensive mandated retrofit.