jQuery Grid Plugin - jqGrid

I have a code like this

jQuery(document).ready(function(){

                $(”#tracuuvetau_button”).click(function (){
                    var gaden = $(”#gaden_sll”).val();
                    var ngaykhoihanh = $(”#datepicker”).val();
                    if((gaden==-1)||(ngaykhoihanh.length==0)){
                        alert(”You haven't given enough infomation”);
                    }
                    else{                       
                        $(”#listsg”).jqGrid({
                            url:'../Route?action=tracuuve&gaden='+gaden+'&ngaykhoihanh='+ngaykhoihanh+'&q=1',
                            datatype:'xml',
                            colNames:['Ma chuyen', 'Ma Tau','Ga den' ,'Ngay khoi hanh','Ngay ket thuc'],
                            colModel:[
                                {name:'machuyen',index:'machuyen', width:80},
                                {name:'matau',index:'matau asc', width:60},
                                {name:'gaden',index:'gaden', width:80},
                                {name:'ngaykhoihanh',index:'ngaykhoihanh', width:150, align:"right"},
                                {name:'ngayketthuc',index:'ngayketthuc', width:150, align:"right"}
                            ],
                            pager: $(”#pagersg”),
                            rowNum: 10,
                            height: 300,
                            width: 650,
                            rowList:[10,20,30],
                            imgpath: '../resources/javascripts/jqGrid/themes/green/images',
                            sortorder: “asc”,
                            viewrecords: true,
                            multiselect: true,
                            caption : “Thong tin ve tau”
                        }).navGrid(”#pagersg”,{refresh: true,edit: true});
                        $(”#listsg”).setGridParam({url:'../Route?action=tracuuve&gaden='+gaden+'&ngaykhoihanh='+ngaykhoihanh+'&q=1'});
                        $(”#listsg”).trigger(”reloadGrid”);
                    }
                });
            });

When i click the button to search infomation the navigation bar appear again like this picture

Plz help me how to make the navigation just appear once times, don't allow it appear again when i click the button

Thanks advance!