A $50 fee to redeem a 50 cent credit? Too bad you’re not flying on Southwest — oh, wait a sec, you are!

Southwest Airlines likes to think of itself a no-fee zone in the skies, with its promises of bags flying free. But it has at least one absurd surcharge of its own, according to Julian Vasquez Heilig.

The carrier recently charged him a $50 fee when he tried to use a 50 cent credit — that’s right, I said cent — on a ticket. Seriously.

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His story shows air travelers must always be on their guard when it comes to fees, even when they’re flying a so-called “no-fee” airline.

Here’s what happened to Heilig:

I am a college professor and I travel frequently on a variety of airlines. Southwest is convenient because they allow bag to fly for free as well as using the amount of a ticket towards a new ticket in the future.

I was amazed when Southwest Airlines took $50 for 50 cents.

I booked a trip to DC in the summer of 2010. About two weeks before I departed, my meeting was changed and I came back a day earlier. I bought a different ticket last year and had a 50 cent balance.

When I booked the DC ticket I used the 50 cents not wanting it to go to waste. In October, I attempted to book a new flight using the DC canceled ticket balance. Southwest informed me that because I had used the 50 cents from last year’s ticket they were going to keep all of the $233 from my ticket that I bought three months ago.

I was shocked.

The customer service agent stated that a special screen had notified me that they would do so. I contested that no such notification had been provided. Eventually, they offered a $50 fee and provided a voucher for $183. I believe that 50 cents for 50 dollars was clearly a steep and unfair (even hidden) fee. Is there anything that can be done?

In fairness to Southwest, it tends to have some of the most reasonable fees in the airline industry. Some of them are outlined here.

But on this one, I’m not sure if it’s doing itself any favors. It should have allowed him to undo the redemption so that he wouldn’t lose $233, or the compromise $50 — and if it did keep the money, it should have at least notified him before the transaction.

Should Heilig have known that this could happen, by making himself aware of Southwest’s policies? No. No reasonable airline passenger can be expected to review all of the fine print and policy associated with a ticket. Even as a frequent Southwest passenger, this isn’t something he should have been aware of, in my opinion.

I contacted Southwest. Within an hour it called Heilig and credited him with $50. A representative blamed the glitch on “the state of their computer system.”

Good work, Southwest.

Update (11:30 a.m.). I asked Heilig to clarify his situation after some commenters said they were confused. On re-reading the post, I can see why they might feel that way. Here’s how he explained it:

I bought a ticket last year. I had to cancel the flight in 2009. I used the balance on another flight in 2009. There was a 50 cent balance from the 2009 ticket.

I bought a new ticket to DC in Summer 2010. I used the 50 cents from the 2009 balance when I purchased the ticket in 2010. I cancelled the ticket in September 2010.

I expected to be able to purchase a new ticket using the balance in October 2010. However, the 50 cents from the 2009 ticket had invalidated the entire balance of the cancelled Summer 2010 ticket to DC of $233 (365 day limit on the 50 cents).

I called Southwest with the issue. They told me the $233 was gone forever because of the expiration date of the 50 cents. I protested. They gave me $183 electronic voucher but took a $50 fee to “reissue.”