Upload file data and variable ajax

Question

I want to upload file data and a variable, when i submit a file it goes well. But if i append the variable there happens nothing. The thing what i see is the file data.

html:

<form id="articleData">
    <input type="hidden" name="id" value="123" readonly="readonly">
    Upload article csv: <input name="articleCsv[]" type="file" /><br />
    <input type="radio" name="item" value="add">Add new items<br>
    <input type="radio" name="item" value="update">Update items

    <input type="submit" value="Submit">
</form>

This is my ajax request:

$("form#articleData").submit(function(event){
  //disable the default form submission
  event.preventDefault();
  var checked = $('input[name=item]:checked', '#articleData').val();
  //grab all form data  
  var formData = new FormData($(this)[0]);
      formData.append('updateOrAdd',checked);

  $.ajax({
    url: "/spares/admin/importArticleCsv",
    type: 'POST',
    data: formData,
    async: false,
    cache: false,
    contentType: false,
    processData: false,
    success: function (returndata) {
      alert(returndata);
    }
  });

  return false;
});

my php:

public function importArticleCsv(){
    $output[] = array();
    $response[] = "";

    $this->load->model('admin/csv');
    $url = $_FILES['articleCsv']['tmp_name'][0];
    $updateOrAdd = $_FILES;
    print_r($updateOrAdd);
    $header = NULL;
    $data = array();

}

And the output of my print_r in the php code

Array
(
    [articleCsv] => Array
        (
            [name] => Array
                (
                    [0] => Pmaster Inladen.csv
                )

            [type] => Array
                (
                    [0] => text/csv
                )

            [tmp_name] => Array
                (
                    [0] => /Applications/AMPPS/tmp/php/php7VNPlg
                )

            [error] => Array
                (
                    [0] => 0
                )

            [size] => Array
                (
                    [0] => 111216
                )

        )

)

Where is my key (updateOrAdd) not in the array? I don't get it..