An April 4 article and graphic incorrectly identified the Reagan National Airport runway used for takeoffs to the north. It is Runway 1. (Published 4/5/02)

The Frontier Airlines flight crew that violated restricted airspace over Washington on Monday flew slightly west of the White House and the Washington Monument, then flew directly over the vice presidential residence on the Naval Observatory grounds while trying to get back on course, aviation sources said yesterday.

Earlier that day, the same crew had been forced to land at Dulles International Airport after failing to properly give the password for permission to fly to its original destination, Reagan National Airport.

The crew's two pilots, who have not been identified, have been suspended pending an investigation by the airline and the Federal Aviation Administration.

FAA spokeswoman Laura Brown said three other commercial flights and a medical helicopter have violated White House airspace since Sept. 11, but none as deeply as the Frontier flight. She said 35 other inbound planes have been diverted to Dulles because of failure to follow proper procedures, with the rate of diversions decreasing steadily each month.

Officials, puzzling yesterday over how one flight crew could make so many mistakes, said the incident involving Frontier Flight 724 points out both the strengths and weaknesses of flight security restrictions at National.

The Secret Service lobbied hard to keep National closed after the Sept. 11 hijackings, sources said, but President Bush decided otherwise after hearing from local officials about the devastating economic impact such a closing would have. Instead, new security measures were imposed, including more searches of passengers and baggage and special flight procedures.

The inbound flight procedures for Flight 724 were clearly successful. Making its initial descent into the Washington area, the plane was ordered to land "short" at Dulles after the crew failed to give the proper password -- which changes daily -- to the proper controller at the proper point.

If necessary, military planes may be called in to escort a plane that fails to give the password, but that apparently did not happen in this case. A North American Aerospace Defense Command spokesman in Colorado Springs was quoted in the Rocky Mountain News as saying the incidents were not deemed threatening by the FAA and there was no reason for NORAD to get involved.

Outbound, however, there is little anyone can do when a flight taking off on Runway 19 to the north does not make the proper left turn over the Potomac River. There has long been an urban legend that Stinger missiles are mounted on the White House roof, but sources said that has never been true. Shooting down a plane approaching the White House would only scatter burning fuel and wreckage over the District.

Numerous precautions are taken to remind pilots that they must make a left turn "as soon as practicable" after liftoff from Runway 19, then fly northwest directly over Rosslyn. The area is highlighted on aviation maps and charts, and there is a large sign at the takeoff end of Runway 19 giving pilots a last reminder. A recorded radio message giving airport and weather conditions, which pilots must monitor, always contains a reminder of the restrictions.

According to aviation sources, an air traffic controller in the National tower cleared Flight 819 to take off about 6:30 p.m., then turned his attention to inbound traffic from the south. When he looked north again, he saw that Flight 819 had not turned and immediately ordered the plane to turn left.

While turning, the plane flew directly over a small area of restricted airspace surrounding the vice president's residence in Northwest Washington.

Restricted airspace, called Area P-56A, covers most of downtown Washington from the Lincoln Memorial to Capitol Hill, and from the Tidal Basin to several blocks north of the White House. Area P-56B is the circle of airspace over the vice presidential residence.

The airspace between the two restricted areas is left open so medevac helicopters can fly to hospitals in the area.

Passengers aboard the inbound Frontier flight were never told why they were landing at Dulles. In fact, passenger Lawrence Kaufman of Denver said that after landing, a flight attendant made an announcement welcoming the passengers to National.

"I knew it wasn't National," said Kaufman, a transportation writer.

"I had a window seat so I was looking for the Potomac," he said. "I knew it was dry in the east but not that dry."

The pilot then announced that the plane had been told to land at Dulles, and said he didn't know why. The plane was surrounded by vehicles with flashing lights and escorted to an area away from the terminal.

The pilot got off the plane, then returned later and the plane took off for National. The passenger said the pilot never gave a reason for the diversion.