A Piedmont Airlines 737 jetliner that rattled windows and frightened office workers in Rosslyn in December was apparently off course and flying lower and closer to the USA Today building than federal guidelines prescribe, the National Transportation Safety Board reported yesterday.
The plane was making an instrument approach to National Airport through low clouds. It apparently passed the USA Today building roughly level with the top floor and closer to the structure than the 500-foot distance pilots are supposed to maintain, the report said. The plane also was at one point apparently as much as 383 feet lower than the 900-foot altitude prescribed, according to the board.
Releasing results of a three-month inquiry into the incident, the board called for flight rule changes intended to help assure that planes on instrument approaches to National keep well above and away from the high-rise office buildings in Rosslyn. At the time of the incident, Piedmont and the Federal Aviation Administration said the plane appeared to have made a normal approach. Piedmont officials declined to comment on the report yesterday, saying they had not yet received it.
Though the Piedmont plane may have come unusually close, the report noted, "occurrence of low-flying airplanes over this section of Rosslyn is not unusual."
The report, sent to the FAA, also said that controllers at National say the airport's system of warning when planes are too low is "unreliable." The board called for a radar antenna to be moved to a site where there would be less interference from buildings around the airport.
The FAA, which has said current procedures are safe, declined to comment on the board's proposals. "We will study the recommendations and give it full consideration," said FAA spokesman Fred Farrar. By law, the FAA is required to respond to the proposals but not necessarily to implement them.
The board called for new rules governing the low visibility aproach from the north, which the Piedmont jet used. Current rules require pilots to be at least at 900 feet altitude at a point just upstream from Rosslyn. If they can see the airport when they reach 720 feet, they are free to continue descending at whatever rate they believe is prudent, according to investigators.
The board wants the rules amended to require that planes stay at 720 feet until they reach the area between the Theodore Roosevelt and Memorial bridges. That, investigators said, would keep planes well above Rosslyn's upper floors.
The board also called on the FAA to realign another low-visibility instrument path that takes planes directly over Rosslyn at an altitude of 1,100 feet. Under the proposal, the path, now a heading of 147 degrees, would be shifted about six degrees to route traffic over the Potomac or closer to the river. This would bring it into line with the approach path used by the Piedmont jet.
Board investigators also proposed that the airport's main radar antenna be moved to improve a warning system that informs the control tower if a plane drops too low. Controllers said there is a "long-standing weakness" in the system, according to the report.
The report said the system can fail when Rosslyn office buildings block the radar signal and called on the FAA to relocate the antenna to improve the system's performance. FAA officials have denied that there is a problem with the warning system.
The board's report may add to the protests of civic groups that allege the current approach paths are unsafe. However, the groups generally want traffic to be sent to Dulles International Airport, rather than going to National by different routes.
Since the beginning of high-rise development in Rosslyn, Arlington County has required developers to get letters from the FAA certifying that their buildings would not pose a hazard to aviation as a condition of construction. FAA examiners review plans for each building and have certified all the buildings as safe for aviation.