function fillCategory(){ 
 // this function is used to fill the category list on load
addOption(document.drop_list.Category, "CTR", "CTR", "");
addOption(document.drop_list.Category, "APP", "APP", "");
addOption(document.drop_list.Category, "TWR", "TWR", "");
addOption(document.drop_list.Category, "GND", "GND", "");
addOption(document.drop_list.Category, "DEL", "DEL", "");
}

function SelectSubCat(){
// ON selection of category this function will work

removeAllOptions(document.drop_list.SubCat);
addOption(document.drop_list.SubCat, "", "Facility", "");

if(document.drop_list.Category.value == 'CTR'){
addOption(document.drop_list.SubCat, "CHI", "Chicago (CHI)");
}
if(document.drop_list.Category.value == 'APP'){
addOption(document.drop_list.SubCat,"CID", "Cedar Rapids (CID)");
addOption(document.drop_list.SubCat,"CMI", "Champaign (CMI)");
addOption(document.drop_list.SubCat,"CHI", "Chicago (CHI)");
addOption(document.drop_list.SubCat,"FWA", "Fort Wayne (FWA)");
addOption(document.drop_list.SubCat,"GRR", "Grand Rapids (GRR)");
addOption(document.drop_list.SubCat,"AZO", "Kalamazoo (AZO)");
addOption(document.drop_list.SubCat,"MSN", "Madison (MSN)");
addOption(document.drop_list.SubCat,"MKE", "Milwaukee (MKE)");
addOption(document.drop_list.SubCat,"MKG", "Muskegon (MKG)");
addOption(document.drop_list.SubCat,"PIA", "Peoria (PIA)");
addOption(document.drop_list.SubCat,"MLI", "Quad City (MLI)");
addOption(document.drop_list.SubCat,"RFD", "Rockford (RFD)");
addOption(document.drop_list.SubCat,"SBN", "South Bend (SBN)");
addOption(document.drop_list.SubCat,"ALO", "Waterloo (ALO)");
}
if(document.drop_list.Category.value == 'TWR'){
addOption(document.drop_list.SubCat,"ARR", "Aurora (ARR)");
addOption(document.drop_list.SubCat,"BMI", "Bloomington (BMI)");
addOption(document.drop_list.SubCat,"BTL", "Battle Creek (BTL)");
addOption(document.drop_list.SubCat,"CID", "Cedar Rapids (CID)");
addOption(document.drop_list.SubCat,"CMI", "Champaign (CMI)");
addOption(document.drop_list.SubCat,"DBQ", "Dubuque (DBQ)");
addOption(document.drop_list.SubCat,"DPA", "Du Page (DPA)");
addOption(document.drop_list.SubCat,"ENW", "Kenosha (ENW)");
addOption(document.drop_list.SubCat,"FWA", "Fort Wayne (FWA)");
addOption(document.drop_list.SubCat,"GRR", "Grand Rapids (GRR)");
addOption(document.drop_list.SubCat,"GYY", "Gary (GYY)");
addOption(document.drop_list.SubCat,"JVL", "Janesville (JVL)");
addOption(document.drop_list.SubCat,"AZO", "Kalamazoo (AZO)");
addOption(document.drop_list.SubCat,"MDW", "Midway (MDW)");
addOption(document.drop_list.SubCat,"MSN", "Madison (MSN)");
addOption(document.drop_list.SubCat,"MKE", "Mitchell (MKE)");
addOption(document.drop_list.SubCat,"MKG", "Muskegon (MKG)");
addOption(document.drop_list.SubCat,"MWC", "Timmerman (MWC)");
addOption(document.drop_list.SubCat,"ORD", "O'Hare (ORD)");
addOption(document.drop_list.SubCat,"OSH", "Oshkosh (OSH)");
addOption(document.drop_list.SubCat,"PIA", "Peoria (PIA)");
addOption(document.drop_list.SubCat,"ARR", "Executive (PWK)");
addOption(document.drop_list.SubCat,"MLI", "Quad City (MLI)");
addOption(document.drop_list.SubCat,"RFD", "Rockford (RFD)");
addOption(document.drop_list.SubCat,"SBN", "South Bend (SBN)");
addOption(document.drop_list.SubCat,"ALO", "Waterloo (ALO)");
addOption(document.drop_list.SubCat,"UES", "Waukesha (UES)");
addOption(document.drop_list.SubCat,"UGN", "Waukegan (UGN)");
}
if(document.drop_list.Category.value == 'GND'){
addOption(document.drop_list.SubCat,"ARR", "Aurora (ARR)");
addOption(document.drop_list.SubCat,"BMI", "Bloomington (BMI)");
addOption(document.drop_list.SubCat,"BTL", "Battle Creek (BTL)");
addOption(document.drop_list.SubCat,"CID", "Cedar Rapids (CID)");
addOption(document.drop_list.SubCat,"CMI", "Champaign (CMI)");
addOption(document.drop_list.SubCat,"DBQ", "Dubuque (DBQ)");
addOption(document.drop_list.SubCat,"DPA", "Du Page (DPA)");
addOption(document.drop_list.SubCat,"ENW", "Kenosha (ENW)");
addOption(document.drop_list.SubCat,"FWA", "Fort Wayne (FWA)");
addOption(document.drop_list.SubCat,"GRR", "Grand Rapids (GRR)");
addOption(document.drop_list.SubCat,"GYY", "Gary (GYY)");
addOption(document.drop_list.SubCat,"JVL", "Janesville (JVL)");
addOption(document.drop_list.SubCat,"AZO", "Kalamazoo (AZO)");
addOption(document.drop_list.SubCat,"MDW", "Midway (MDW)");
addOption(document.drop_list.SubCat,"MSN", "Madison (MSN)");
addOption(document.drop_list.SubCat,"MKE", "Mitchell (MKE)");
addOption(document.drop_list.SubCat,"MKG", "Muskegon (MKG)");
addOption(document.drop_list.SubCat,"MWC", "Timmerman (MWC)");
addOption(document.drop_list.SubCat,"ORD", "O'Hare (ORD)");
addOption(document.drop_list.SubCat,"OSH", "Oshkosh (OSH)");
addOption(document.drop_list.SubCat,"PIA", "Peoria (PIA)");
addOption(document.drop_list.SubCat,"ARR", "Executive (PWK)");
addOption(document.drop_list.SubCat,"MLI", "Quad City (MLI)");
addOption(document.drop_list.SubCat,"RFD", "Rockford (RFD)");
addOption(document.drop_list.SubCat,"SBN", "South Bend (SBN)");
addOption(document.drop_list.SubCat,"ALO", "Waterloo (ALO)");
addOption(document.drop_list.SubCat,"UES", "Waukesha (UES)");
addOption(document.drop_list.SubCat,"UGN", "Waukegan (UGN)");
}
if(document.drop_list.Category.value == 'DEL'){
addOption(document.drop_list.SubCat,"CID", "Cedar Rapids (CID)");
addOption(document.drop_list.SubCat,"CMI", "Champaign (CMI)");
addOption(document.drop_list.SubCat,"DPA", "Du Page (DPA)");
addOption(document.drop_list.SubCat,"FWA", "Fort Wayne (FWA)");
addOption(document.drop_list.SubCat,"GRR", "Grand Rapids (GRR)");
addOption(document.drop_list.SubCat,"AZO", "Kalamazoo (AZO)");
addOption(document.drop_list.SubCat,"MSN", "Madison (MSN)");
addOption(document.drop_list.SubCat,"MKE", "Mitchell (MKE)");
addOption(document.drop_list.SubCat,"PWK", "Executive (PWK)");
addOption(document.drop_list.SubCat,"PIA", "Peoria (PIA)");
addOption(document.drop_list.SubCat,"MLI", "Quad City (MLI)");
addOption(document.drop_list.SubCat,"ORD", "O'Hare (ORD)");
addOption(document.drop_list.SubCat,"RFD", "Rockford (RFD)");
addOption(document.drop_list.SubCat,"SBN", "South Bend (SBN)");
addOption(document.drop_list.SubCat,"MDW", "Midway (MDW)");
}
}
////////////////// 

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);
}