U.S. airlines continue to collect record fees from passengers who check suitcases or make changes to their reservations. In the first three months of this year, airlines took in $1.6 billion in such fees, up 7.4 percent from the same period last year.

That’s the highest amount for the first quarter since bag fees started in 2008, according to data from the Bureau of Transportation Statistics. Those months are traditionally the slowest for air travel.

These add-on charges, along with falling jet fuel prices, helped airlines post a combined $3.1 billion in profits during the first quarter. That was a net profit margin of 8 percent, a significant jump up from the 1.3 percent margin in the year before.

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Photo Credit: Luggage waits to be run through the baggage system for testing in the new Maynard Holbrook Jackson Jr. International Terminal at Atlanta's airport. David Goldman / Associated Press