Oh yes, indeed. The certification process of every aircraft that we go through involves stumbling over problems that we cannot perceive.
I'm sure many of you have wondered why it has taken so long to get the Max back in service. It is a result of the certification process. There have been three iterations, and still one to go with the software patch that Boeing is developing because partway through the development of the software patch more problems were discovered and they had to fix them. That's one of the benefits of the certification process. You have the opportunity to wring it out, to test the system, to prove that it operates. If you discover a problem, you do not proceed. You go back and fix it.
That's why we're still sitting here today with the 737 Max on the ground.