function fillCategory(){ 
 // this function is used to fill the category list on load
   addOption(document.drop_list.Category, "AMS", "Amsterdam");
   addOption(document.drop_list.Category, "BKK", "Bangkok");
   addOption(document.drop_list.Category, "PEK", "Beijing");
   addOption(document.drop_list.Category, "BOM", "Bombay/Mumbai");
   addOption(document.drop_list.Category, "BOS", "Boston");
   addOption(document.drop_list.Category, "PUS", "Busan");
   addOption(document.drop_list.Category, "DTW", "Detroit");
   //addOption(document.drop_list.Category, "DUS", "Dusseldorf");
   addOption(document.drop_list.Category, "FRA", "Frankfurt");
   addOption(document.drop_list.Category, "GUM", "Guam");
   addOption(document.drop_list.Category, "CAN", "Canton/Guangzhou");
   //addOption(document.drop_list.Category, "BDL", "Hartford");
   addOption(document.drop_list.Category, "HKG", "Hong Kong"); 
   addOption(document.drop_list.Category, "HNL", "Honolulu");
   addOption(document.drop_list.Category, "LAX", "Los Angeles");
   addOption(document.drop_list.Category, "LGW", "London-Gatwick");
   addOption(document.drop_list.Category, "LHR", "London-Heathrow"); 
   addOption(document.drop_list.Category, "MNL", "Manila");
   addOption(document.drop_list.Category, "MEM", "Memphis");
   addOption(document.drop_list.Category, "MSP", "Mpls/St. Paul");
   addOption(document.drop_list.Category, "NGO", "Nagoya");
   addOption(document.drop_list.Category, "KIX", "Osaka");
   addOption(document.drop_list.Category, "CDG", "Paris");
   addOption(document.drop_list.Category, "PDX", "Portland");
   addOption(document.drop_list.Category, "SPN", "Saipan");
   addOption(document.drop_list.Category, "SFO", "San Francisco");
   addOption(document.drop_list.Category, "SEA", "Seattle");
   addOption(document.drop_list.Category, "ICN", "Seoul"); 
   addOption(document.drop_list.Category, "PVG", "Shanghai");
   addOption(document.drop_list.Category, "SIN", "Singapore");
   addOption(document.drop_list.Category, "TPE", "Taipei");
   addOption(document.drop_list.Category, "NRT", "Tokyo");
}

function SelectSubCat(){
   removeAllOptions(document.drop_list.SubCat);
   addOption(document.drop_list.SubCat, "", "Select City", "");

   if(document.drop_list.Category.value == 'AMS'){
      addOption(document.drop_list.SubCat, "BOM", "Bombay/Mumbai");
      addOption(document.drop_list.SubCat, "BOS", "Boston");			
      addOption(document.drop_list.SubCat, "DTW", "Detroit");
      //addOption(document.drop_list.SubCat, "BDL", "Hartford");
      addOption(document.drop_list.SubCat, "MEM", "Memphis");
      addOption(document.drop_list.SubCat, "MSP", "Mpls/St. Paul");
      addOption(document.drop_list.SubCat, "SEA", "Seattle");
   }

   if(document.drop_list.Category.value == 'BOM'){
      addOption(document.drop_list.SubCat, "AMS", "Amsterdam");
   }
   if(document.drop_list.Category.value == 'BDL'){
      addOption(document.drop_list.SubCat, "AMS", "Amsterdam");
   }
   if(document.drop_list.Category.value == 'BOS'){
      addOption(document.drop_list.SubCat, "AMS", "Amsterdam");
   }
   if(document.drop_list.Category.value == 'BKK') {
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
   if(document.drop_list.Category.value == 'CAN') {
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
   if(document.drop_list.Category.value == 'PEK') {
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
   if(document.drop_list.Category.value == 'PVG') {
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
   if(document.drop_list.Category.value == 'SIN') {
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
   if(document.drop_list.Category.value == 'PUS') {
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
   if(document.drop_list.Category.value == 'MSP'){
      addOption(document.drop_list.SubCat, "AMS", "Amsterdam");
      addOption(document.drop_list.SubCat, "LHR", "London-Heathrow");
      //addOption(document.drop_list.SubCat, "CDG", "Paris");
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
   if(document.drop_list.Category.value == 'DTW'){
      addOption(document.drop_list.SubCat, "AMS", "Amsterdam"); 
      //addOption(document.drop_list.SubCat, "DUS", "Dusseldorf");
      addOption(document.drop_list.SubCat, "FRA", "Frankfurt");
      addOption(document.drop_list.SubCat, "LGW", "London-Gatwick");
      addOption(document.drop_list.SubCat, "LHR", "London-Heathrow");
      addOption(document.drop_list.SubCat, "KIX", "Osaka");
      addOption(document.drop_list.SubCat, "NGO", "Nagoya");
      addOption(document.drop_list.SubCat, "CDG", "Paris");
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
   if(document.drop_list.Category.value == 'MEM'){
      addOption(document.drop_list.SubCat,"AMS", "Amsterdam");
   }
   if(document.drop_list.Category.value == 'DUS') {
      //addOption(document.drop_list.SubCat, "DTW", "Detroit");
   }
   if(document.drop_list.Category.value == 'FRA') {
      addOption(document.drop_list.SubCat, "DTW", "Detroit");
   }
   if(document.drop_list.Category.value == 'CDG') {
      addOption(document.drop_list.SubCat, "DTW", "Detroit");
      //addOption(document.drop_list.SubCat, "MSP", "Mpls/St. Paul");
   }
   if(document.drop_list.Category.value == 'GUM') {
      addOption(document.drop_list.SubCat, "NGO", "Nagoya");
      addOption(document.drop_list.SubCat, "KIX", "Osaka");
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
   if(document.drop_list.Category.value == 'HKG') {
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
   if(document.drop_list.Category.value == 'HNL') {
      addOption(document.drop_list.SubCat, "KIX", "Osaka");
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
  if(document.drop_list.Category.value == 'ICN') {
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
   }
  if(document.drop_list.Category.value == 'KIX') {
      addOption(document.drop_list.SubCat, "DTW", "Detroit");
      addOption(document.drop_list.SubCat, "GUM", "Guam");
      addOption(document.drop_list.SubCat, "HNL", "Honolulu");
      addOption(document.drop_list.SubCat, "SPN", "Saipan");
      addOption(document.drop_list.SubCat, "TPE", "Taipei");
  }
  if(document.drop_list.Category.value == 'LAX') {
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
  }
  if(document.drop_list.Category.value == 'LGW') {
      addOption(document.drop_list.SubCat, "DTW", "Detroit");
  }
  if(document.drop_list.Category.value == 'LHR') {
      addOption(document.drop_list.SubCat, "DTW", "Detroit");
      addOption(document.drop_list.SubCat, "MSP", "Mpls/St. Paul");
      addOption(document.drop_list.SubCat, "SEA", "Seattle");
  }
  if(document.drop_list.Category.value == 'MNL') {
      addOption(document.drop_list.SubCat, "NGO", "Nagoya");
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
  }
  if(document.drop_list.Category.value == 'NGO') {
      addOption(document.drop_list.SubCat, "DTW", "Detroit");
      addOption(document.drop_list.SubCat, "GUM", "Guam");
      addOption(document.drop_list.SubCat, "MNL", "Manila");
      addOption(document.drop_list.SubCat, "SPN", "Saipan");
  }
  if(document.drop_list.Category.value == 'NRT'){
      addOption(document.drop_list.SubCat, "BKK", "Bangkok");
      addOption(document.drop_list.SubCat, "PEK", "Beijing");
      addOption(document.drop_list.SubCat, "PUS", "Busan");
      addOption(document.drop_list.SubCat, "DTW", "Detroit");
      addOption(document.drop_list.SubCat, "GUM", "Guam");
      addOption(document.drop_list.SubCat, "CAN", "Canton/Guangzhou");
      addOption(document.drop_list.SubCat, "HKG", "Hong Kong");
      addOption(document.drop_list.SubCat, "HNL", "Honolulu");
      addOption(document.drop_list.SubCat, "LAX", "Los Angeles");
      addOption(document.drop_list.SubCat, "MNL", "Manila");
      addOption(document.drop_list.SubCat, "MSP", "Mpls/St. Paul");
      addOption(document.drop_list.SubCat, "PDX", "Portland");
      addOption(document.drop_list.SubCat, "SPN", "Saipan");
      addOption(document.drop_list.SubCat, "SFO", "San Francisco");
      addOption(document.drop_list.SubCat, "SEA", "Seattle");
      addOption(document.drop_list.SubCat, "ICN", "Seoul");
      addOption(document.drop_list.SubCat, "PVG", "Shanghai");
      addOption(document.drop_list.SubCat, "SIN", "Singapore");
  }
  if(document.drop_list.Category.value == 'PDX') {
      addOption(document.drop_list.SubCat, "AMS", "Amsterdam");
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
  }
  if(document.drop_list.Category.value == 'SEA') {
      addOption(document.drop_list.SubCat, "AMS", "Amsterdam");
      addOption(document.drop_list.SubCat, "LHR", "London-Heathrow");
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
  }
  if(document.drop_list.Category.value == 'SFO') {
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
  }
  if(document.drop_list.Category.value == 'SPN') {
      addOption(document.drop_list.SubCat, "NGO", "Nagoya");
      addOption(document.drop_list.SubCat, "KIX", "Osaka");
      addOption(document.drop_list.SubCat, "NRT", "Tokyo");
  }
  if(document.drop_list.Category.value == 'TPE') {
      addOption(document.drop_list.SubCat, "KIX", "Osaka");
  }

}

function removeAllOptions(selectbox) {
   var i;
      for(i=selectbox.options.length-1;i>=0;i--) {
         //selectbox.options.remove(i);
	 selectbox.remove(i);
      }
}


function addOption(selectbox, value, text) {
   var optn = document.createElement("OPTION");
   optn.text = text;
   optn.value = value;

   selectbox.options.add(optn);
}