London's Heathrow Airport, which has been off limits to Twin Cities travelers who wanted to fly there nonstop, will have direct service from Northwest Airlines starting in the spring.

Northwest will begin the service March 29, replacing the current daily flight between the Twin Cities and Gatwick Airport south of London.

Heathrow is a more attractive destination than Gatwick because it is roughly half the distance from central London and that city's financial district.

"It's a destination and an airport that we've always wanted to provide," Laura Liu, Northwest's senior vice president, international, said Monday. "Now with the open skies agreement, we can do that."

Earlier this year, the European Union approved an "open skies" agreement that lifted restrictions on the number of airlines allowed to fly between the United States and European cities.

Only four carriers -- American Airlines, United Airlines, British Airways and Virgin Atlantic -- currently have the right to fly nonstop between the United States and Heathrow.

Soon, Northwest, Delta Air Lines and Continental Airlines will be entering the Heathrow market as a result of the new agreement.

Northwest's daily flight will leave the Twin Cities at 9:30 p.m.

It will use an Airbus A330-300, which seats 298 passengers. In May, Northwest will add a daily flight to Heathrow from Detroit, and in June a Seattle flight will begin. While the Twin Cities flight to Gatwick will be eliminated, a Gatwick flight will be retained in the Detroit market on a smaller airplane, a Boeing 757.

Delta said in October that it will continue to operate seven daily flights in the London market, but three of those will head to Heathrow. Starting March 29, Delta will fly once a day from Atlanta to Heathrow and twice a day from New York's Kennedy Airport to Heathrow.

Continental said in November that it will fly twice-daily from Newark and Houston to Heathrow. Like Delta, it will keep some service to Gatwick.

Despite the larger number of carriers that will be serving Heathrow, Liu said, "Northwest can compete and do well in this market."

Bill Swelbar, an airline expert at the Massachusetts Institute of Technology, said: "We have to expect that there is going to be some very aggressive competition for passengers now going to Heathrow that had limited opportunities before." Now, he said, several major hubs are going to have nonstop Heathrow service.

During the past several weeks, Liu said, she has not seen a pattern of reduced fares from carriers marketing summer flights to Heathrow.

Deborah Callahan, president and CEO of Corporate Travel Solutions, St. Paul, said the new service will give Northwest's business travelers the option of reaching a prime European airport.

"We think of Amsterdam as being a major global hub," said Callahan, who advises corporations on business travel. She added the Heathrow service "will be advantageous for those travelers connecting onward to destinations within Europe" and other parts of the world.

Northwest is gaining access to Heathrow through its alliance partner KLM Royal Dutch Airlines, which is making airport slots available to Northwest. Terms of their slot agreement were not available.

This marks the second time in recent months that Northwest has improved its Twin Cities international service. Northwest will begin daily nonstop service between the Twin Cities and Paris on April 8. The carrier also flies to Amsterdam and Tokyo from the Twin Cities.

Liz Fedor • 612-673-7709