Ever try to redeem your hard-earned frequent flyer miles for a "free" international award trip only to discover the taxes were several hundred dollars?

For those who think that airfare is through the roof these days, it might not always be about a greedy airline trying to fill its coffers with fuel surcharges and fees. Part of the cost of your flight comes from airports that charge the airlines fees for using their facilities in the form of landing or fueling fees. These are bundled into the price of your airfare, but there are some additional taxes that airports impose on the airlines that are passed on to consumers, and they vary from airport to airport. These fees can add up when traveling internationally, and when you redeem your miles the airline will pass these costs on to you.

Each time a ticket is issued, there is a breakdown of the taxes listed on your receipt (you know, that email the airline sends you).  Domestic taxes are fairly simple, but international taxes are complicated and can sometimes be avoided or reduced depending on the airports through which you connect.  The same fees are added to airline tickets you buy with cash, but there's just something irritating about paying a ton in taxes on a so-called free ticket.

So first, what are these taxes? Many of them are flat taxes and aren't based on a percentage of your ticket's price, meaning if you are redeeming a mileage ticket or paying for it, you pay the same taxes. For example, an airport or passenger facility tax, which is payable to the airport authority, covers the facility maintenance or upgrades of an airport. Some airports even charge fees for noise reduction efforts. Why should you foot the bill if you don't even live there? Or if you pass through an airport undergoing major renovations, and you may be paying for those upgrades yourself.

The U.S. charges similar fees on domestic tickets including the Sept. 11 fee of $2.50 per flight (with a maximum charge of $10 per total ticket) to cover increased security measures. But, that is nowhere near as high as what other countries are charging. 

Airfarewatchdog takes a look at how the airports that you choose to connect through on your overseas trips may be costing you bundles for that layover (that you do not even want in the first place).

Here are some examples of taxes and fees imposed when connecting through certain hub airports. Keep in mind that the size of the tax sometimes depends on the length of the flight (long-haul vs. short-haul) and if flying to, from or through the U.K. can even vary depending on the class of service (first, business, economy), so we compared apples to apples using the same flight routing. The example below shows the variation in airport fees on one award routing. If you are making multiple stops on an itinerary, it can really add up.

Connecting city airport taxes on a JFK-Rome-JFK roundtrip flight Sept. 1-6, 2011

$34 with Air Europa via Madrid, Spain:

Airport Service Charge $26

Airport Security Fee $8

$44 with KLM via Amsterdam, Netherlands:

Passenger Service Charge $18

Airport Security Fee $20

Noise Isolation Surcharge $6

$59 with Swiss International via Zurich, Switzerland

Passenger/Airport/Noise Cancelation Fee $59

$63 with British Airways via London Heathrow

Passenger/Airport Fee $63 (economy class)

$69 with Lufthansa via Frankfurt, Germany

Passenger Service Charge $51

Airport Security Fee $18

$85 with Air France via Paris CDG

Civil Aviation Tax $18

Passenger Service Charge $30

Airport Tax $37

Cheapest airport to connect through: Madrid, Spain

Most Expensive airport to connect through: Paris, France

In another more complicated example, say you are traveling from JFK to Cairo with a double connection in both Amsterdam and Paris because that was the only award ticket or routing that was available. Well, you'll be forking over the $85 for a connection in Paris and $44 for a connection in Amsterdam. Each way! And per ticket! So it's wise to study your options when you have multiple connecting cities to choose from on a given itinerary, especially if you're paying with miles to get a "free" trip. Learn the main hubs of the airlines and their partners with which you collect most of your airline miles. Wait for a single connection through Amsterdam to become available or try a different connecting city.

Ask the reservations agent when booking the ticket to see which airports are charging the highest taxes. Or study the online receipt fine print before clicking "confirm" on your reservation.