Originally Posted by
Grebe
And how much cost and whom pays for part failing prematurely ?
Boeing typically guarantees a certain cycle/hour fatigue life, and Boeing would cover at least part of the repair costs assuming it failed below those life limits.
However,
if the cracks are indeed associated with retrofit winglets - that's an STC outside of Boeing's direct control and all bets are off.
I do know that new build 737s with winglets get changes to the wing structure to account for the different loads and load paths associated with the winglets. I don't know about the 737, but I used to know a guy that worked for the company that did the STC winglet mod for the 757 and 767 - he said the structural changes they needed to make to the wings were extensive (and expensive) - but the fuel burn savings were so high that for longer range aircraft the payback only took about a year.