well first of all everybody clears CASS. in fact there is no pass or fail and all of them will be called for the GD & interview.
as for the interview my experience says that u have to confident and honest
. expect questions on the technical aspects , meteorology and lots of aerodynamics. these three are huge subjects so lots of study is required.
there will also be some really difficult HR questions
for which u wont find answers in any book.its only up to you.
in the end its all about being calm ,cool and confident (CCC)
all the best