Baggage bins above airline seats are getting more and more crowded. As baggage fees go up, passengers are carrying more on board aircraft. But more and more travelers are starting to gate-check luggage as well. It seems to be a loophole in the airline baggage check fee system.

Just this month, Continental, Delta, United and American all began charging coach passengers on domestic flights $25 for a first checked bag and $35 for the second, an increase of about $5 over previous fees. USAirways raised their fee in December. (There are some bargains for online payments.)

Is it too much of a coincidence that these increases came for the most part after the Christmas bombing attempt and security for carry-on bags became more of a hassle?

I fly regularly between Boston and Washington DC. Almost every aircraft I have been on in the past year has been a smaller regional aircraft. Gate-checking is the norm for anything larger than a briefcase or thin computer bag. There simply is no room on the small plane for more, especially when traveling on American Airlines regional jets.

However, on a couple of recent trips across the country I noticed that more and more bags seem be finding their way into gate-check collections of strollers and car seats at the end of the Jetway.

It seems that many business travelers and some leisure travelers are wising up to the fact that airlines only charge luggage fees when passengers check their baggage prior to boarding the flight. If passengers can get to the gate with luggage too large to slip into overhead storage or under the seat, or if there is just no more room on board for more carry-on bags, the attendants simply slap a tag on the bag and gate-check it.

I’m not sure how all of this will play out. I have seen airline staff examining bags in the security line and telling passengers that the bag should be checked rather than carried on. However, when most security lines handle many different airline, it is difficult for airlines to identify their passengers. I have also seen gate personnel offering to check bags that have come through security for free, just to eliminate the hassles of trying to squeeze them on board crowded flights.

Some airlines have tried to put templates on the x-ray machines at security lines, only to have to remove them. Passengers are now wearing vests and jackets with large pockets that act as wearable luggage — certainly stretching the definition of luggage and baggage.

All of these machinations are the result of baggage fees and all were predicted as fees went into effect. Now some legacy carriers are claiming that they will start to charge baggage fees for any luggage that does not fit into the luggage template at the gate.

My prediction: The boarding process will get worse before it gets better because airlines will start stationing a baggage agent at the gate complete with a credit card machine, just like they are using for on-board purchases.

Airline are grubbing for money and they are irritating their passengers. It is not a good combination.