After 18 years operating two daily flights to London from Philadelphia, British Airways will drop one of them in March.

American Airlines, which is British Airways' business partner and member of the same Oneworld airline alliance, will add a second daily flight between Philadelphia and London, effective March 25.

So Philadelphia-area travelers will still have three flights a day across the pond, two operated by American and one by British Airways.

British Airways did not say Thursday why the London-based carrier was discontinuing a flight that's been around since May 1998, or whether the decision was related to Brexit — the U.K.'s decision to  quit the European Union. The weaker pound may depress demand among business travelers but makes the U.K. more attractive to tourists.

British Airways spokeswoman Michele Kropf said the decision was made "in scheduling and reviewing our services with American. We still have a daily flight. It leaves slightly earlier, but we still offer the daily flight."

American, which has a hub in Philadelphia,  "constantly evaluates our transatlantic business with longtime partner British Airways to align schedules across our joint business network," said spokeswoman Victoria Lupica.

British Airways said, "Customers will continue to enjoy quick, smooth connections for onward flights through the coordinated schedules of both airlines, and members of the American AAdvantage and British Airways Executive Club programs can earn and redeem points or miles on codeshare flights."

American will use Airbus A330-300 aircraft with 28 fully lie-flat seats in the Business  cabin and 263 seats in the main coach cabin.

Philadelphia airport officials said the overall seats on the PHL-London route will increase. British Airways will use a larger "high density"  Boeing 747 aircraft with more business-class seats than it currently flies, said airport spokeswoman Mary Flannery.

Under the new schedule,  the British Airways flight will leave PHL at 6:20 p.m.  American's flights will depart at  7:20 p.m. and at 8:45 p.m.  Return flights will leave London at 12:45 p.m. on British Airways and at 10:05 a.m. and 2:10 p.m. daily on American 

The flight being dropped is a 10 p.m. departure to London, with a return flight leaving London at 5:15 p.m. daily.

Jeffrey Erlbaum, president of ETA Travel in Conshohocken, said he was sorry to see the second British Airways flight disappear.  The 10 p.m. flight made sleeping on the plane and adjusting to jet lag "much easier," he said. "They called it a sleeper flight. Coming back, if you were connecting from Europe or even parts of Asia," the 5 p.m. flight was ideal. "If you have business in the U.K. you have most of the day."

British Airways has four classes of service on its  flights: first, business, premium economy, and economy.  "Premium economy is a really nice product and I sell a fair amount of that," Erlbaum said.

"None of the American carriers have it. It's akin to first class on a domestic flight.  You get a wider seat,  more legroom. It's a separate cabin, a nice bump up from coach.  A lot of business travelers use it because it's quite a  bit cheaper than business class."