Authorities were concerned with terrorism threats in the air and on the ground Saturday. The British government delayed a London-to-Washington flight for three hours and U.S. officials monitored heavily secured stadiums hosting the first round of football playoffs.

British Airways 223 (search), the most scrutinized flight since the United States declared a high terrorism alert Dec. 21, lifted off from Heathrow Airport just after 1 p.m. EST after intensive security checks and landed safely near Washington about 8 hours later.

It took nearly an hour for all the passengers to get off the plane and make it to the terminal area at Dulles International Airport (search) in suburban Virginia.

"There was a lot of security but we felt it was necessary due the sensitivity of what was going on here," passenger Joel Ginsburg told WTTG-TV in Washington. He said there was nervousness among passengers, "but the BA people were very good and reassured us the security was tight as a drum and we were going to go for it."

"It was somber," he said of the preflight mood in London. "It was like you could hear a pin drop in the gate area."

But he said applause broke out after the big jet landed.

"It was a little bit scary there (in London)," passenger Jim McCutchan told WRC-TV. "There were about four or five guards at the gate, it looked like carrying AK-47s. It looked like they really meant it. It was a real serious situation."

The plane had the all-clear earlier from Britain's Transport Department (search). The subsequent checks added to the misery of passengers on a flight also detained in Washington on Wednesday and canceled Thursday and Friday.

The British government has declined to provide details of its security concerns about the flight. The department said it took action Saturday following discussions "with a variety of sources," including U.S. authorities.

A British Airways morning flight to Washington D.C. left on schedule at 5:55 a.m. EST Saturday.

Other routes under scrutiny during the code orange alert in the United States were London-Riyadh, Saudi Arabia, and Mexico City-Los Angeles.

The United States is working closely with other countries to lessen the threat of terrorism on international flights.

South Korea's national police agency, responding to American requests for international cooperation, said it would have armed officers on individual U.S.-bound flights if warranted, based on information about a terrorist threat to any specific flight.

Homeland Security Department (search) spokesman Brian Roehrkasse said Saturday that authorities have been discussing security with the National Football League and the National Collegiate Athletic Association during the playoff and college bowl season.

NFL (search) playoff games Saturday were in Baltimore and Charlotte, N.C., with contests Sunday in Green Bay, Wis., and Indianapolis. There were weekend bowl games in Boise, Idaho, and New Orleans.

NFL spokesman Joe Browne said security has been tight since the Sept. 11 attacks, and air space over stadiums is restricted by federal legislation.

He said security for the Super Bowl, Feb. 1 in Houston, would be even more intense because of the international attention the event receives.

"The number one concern our fans have is the air space," he said. Spectators are less concerned about stadium security because "they see our tightened measures as they enter the gates and the parking lots."