American Airlines started using biometric screening for customers boarding flights at Dallas Fort Worth International Airport this week, the company announced Tuesday.The service is available for select international flights. DFW is the largest hub for American Airlines and approximately 10 percent of its over 900 daily flights out of the airport are to international destinations.American started using the technology at Los Angeles International Airport in December. Delta Air Lines is using it for international passengers at a handful of airports, including Atlanta's Hartfield-Jackson, Salt Lake City and Minneapolis.Cedric Rockamore, American vice president of DFW Hub Operations, said in a prepared statement that using biometric screening provides a “more seamless and modern experience for both our customers and team members.”The technology is currently being used in Terminal D with plans to expand the service to Terminals A, B, and C by the end of the year, American said.Here's how it works: Customers will have their faces scanned as they're about to board a flight, then the scanned image will be compared to an existing photo in the U.S. Customs and Border Protection database. If it's a match, the customer will be cleared to board. The process is supposed to take seconds.Customers can still opt to have their passports and boarding passes checked the old-fashioned way, too. American will evaluate the program's effectiveness and consider expansion of the technology at more airports.Biometric screening is becoming more popular with airlines. Last November, Delta Air Lines Inc. (NYSE: DAL) implemented the technology at its Hartsfield-Jackson Atlanta International Airport hub.