jQuery Datatable custom sort

Hey guys so i got this datatable

var oTable = $("#products").dataTable({
    "aaData": [
        [1, "TEST1", "A"],
        ['NA', "NA1", "B"],
        ['NA', "NA2", "C"],
        [4, "TEST2", "D"]
    ],
    "aoColumns": [{
        "sWidth": "70%",
        "sClass": "center",
        "bSortable": true,
        "sType": "rankedNA"

    }, {
        "sWidth": "70%",
        "sClass": "center",
        "bSortable": false
    }, {
        "sWidth": "70%",
        "sClass": "center",
        "bSortable": false
    }]

});

I need a custom sort

    jQuery.fn.dataTableExt.oSort['rankedNA-asc']  = function(a, b) {
        return rankedNASort(a, b);
    };

That always leaves the 'NA' values in the first column at the bottom of the table. No matter if its asc or desc, NA should be fixed at the bottom