$(document).ready(function() {
    $("select#fly").change(function() {
        var ff = $("#fly").val();
        var nights = $('select#fly option:selected').text();
        var datastring = 'a=fp&dep='+ff+"&nights="+nights;
        $.getJSON("/root/flight_dates.php?" + datastring,{id: $(this).val(), ajax: 'true'}, function(j){
            var options = '';
            for (var i = 0; i < j.length; i++) {
                options += '<option value="' + j[i].optionValue + '">' + j[i].optionDisplay + '</option>';
            }
            $("#return_id").html(options);
        });
    });
});