Hello,
First of all, all three of those accidents were the result of pilot error, not airframe failure. But they tried to imply that the airframe failure = the age of the airframes + the phase of flight
The point is not really why those planes go to ground and crash (pilot errors .. malfunction of some equipements .. etc ..) but instead what was the result when they make contact with the ground.
As the document want to show .. they broked in 3 parts ... almost same place for the 3 aircrafts shows in the document.