I have a good memory, I remember.
You had asked whether airlines sometimes pass the buck to airports. It has happened. My colleague Mr. Charbonneau did not remember, but having filed a number of complaints myself and having been front and centre, I remember a clear example involving Vueling Airlines, whose head office is in Barcelona. The company, subject to European regulations, had a three-hour delay. However, it invoked section 3 on compensation, saying that it was not at fault and passing the buck to the airport whose check-in system was down.
Finally, the conclusion was that the circumstances were not extraordinary, since that was part of Vueling's activities, and the company was used to working with airports and check-in systems.
Once again, the extent of the liability is not clear. Is Vueling fully responsible or does half of the responsibility fall on the airport? That's not clear at all. Earlier, I heard comments to that effect, and perhaps the extent of responsibility should be clarified.