Looks like a hard and technical question which has not been clarified yet from the Italian Transportation Safety Board.
There's a nice web-site in which the Itavia accident is explained quite well but unfortunately in Italian only.
Click Here !!!
Hope you have a translator.
Otherwise, sorry to say that, I really have no idea. The Itavia accident has been surrouned since 1980 from silence, lies, and different versions. Today the only thing we know is that 80 or more souls died in that accident. Another example of ITALY = BANANA REPUBLIC !