... I need the previous value of @data ...

If you mean you need to return the element in the  @data array immediately prior to the first element in the array that matches the string passed into the function, I think I would use something like this (Update: an empty string is returned if no match):

>perl -wMstrict -le
"print get_IATA('bar');
 ;;
 sub get_IATA {
   my ($airline) = @_;
   ;;
   my @data = qw(fee fie foe foo barbell boff);
   ;;
   for my $i (1 .. $#data) {
     return $data[$i - 1] if $data[$i] =~ m{ \A \Q$airline\E }xms;
     }
   return '';
   }
"
foo
[download]

Update: Here's a variation that returns every element in the  @data array immediately prior to an element in the array that matches the string passed into the function. An empty list is returned if no match.

>perl -wMstrict -le
"printf qq{'$_' } for get_IATA('bar');
 ;;
 sub get_IATA {
   my ($airline) = @_;
   ;;
   my @data = qw(fee fie yyy barfly foe fum zzz barbell foo);
   ;;
   return
     map { $data[$_] =~ m{ \A \Q$airline\E }xms ? $data[$_ - 1] : () }
     1 .. $#data
     ;
   }
"
'yyy' 'zzz'
[download]