JSONResponseString might be something like this:

{
   "data":[
      {
         "fleet_id":"2",
         "fleet":"EMB195"
      },
      {
         "fleet_id":"3",
         "fleet":"EMB175"
      },
      {
         "fleet_id"         ‌​:"1",
         "fleet":"DHC84-400Q"
      }
   ]
}

procedure TForm1.Button1Click(Sender: TObject);
var
  I: Integer;
  JSONPair: TJSONPair;
  JSONArray: TJSONArray;
  JSONObject: TJSONObject;
begin
  JSONObject := TJSONObject.Create(JSONResponseString);
  try
    JSONArray := JSONObject['data'].AsArray;
    for I := 0 to JSONArray.Size - 1 do
    begin
      JSONPair := JSONArray.Get(I);
      Memo1.Lines.Add(JSONPair.JsonString + ': ' + JSONPair.JsonValue)
    end;
  finally
    JSONObject.Free;
  end;
end;