Bienvenue!
I think Monsieur is asking 3 questions;
Why did the DC-9 suffer from technical problems, and suffer fatal crashes early in its career (value jet and air Canada)
Why did the Caravelle not have the same success as the DC-9 and 737
I think the last question is why the. DC-9 wasn't more successful in Europe, as it was very successful in America, being produced in 80-110 seat versions
Apologies if these aren't exactly correct, and I'm afraid I have no answers, someone else perhaps?
Any spelling mistakes are tablet induced.
TTR