Something similar happened over Amsterdam called ''the Bijlmer disaster''.
An El AL 747 lost two of its engines on one side loosing also hydrolics. Crashed into two flats.
I believe after this happend the pylons of the engines on all 747's with these kind of engines had to be inspected or modified.
Maybe this one was skipped.
I would like to know what the NTSB has to say about this.