Just a small point for the answer
glhcarl gave, what you are refering to is not the life limit that l was refering to.
What you are refering to are the ALI inspections, which on Boeing a/c kick in at around 20000 to 50000 cycles, but on Airbus a/c kick in earlier and are a more in line with routine inspections. All these ALI inspections are mandatory and can not be extended, so no variations unlike normal inspections.
On Airbus all these inspections are carried out until the LOV (Limit of Validity)(ESG) and then your airworthiness certificate ends. I guess that some a/c depending on operations may then get special permits to operate as the Vulcan in the UK.
Boeing a/c just have the figure to start the inspections from as they have not published the DSG, ESG or LOV yet, but l have seen the list which covers all Boeing including Douglas a/c, which will published in due course.
