A backup radar system that severely malfunctioned at Baltimore-Washington International Airport in late August -- leaving air controllers blind to hundreds of planes flying through the air for 27 hours -- failed again during a test Sunday, according to air traffic employees.
The system, known as CENRAP, performed so poorly during the test early Sunday morning that it was shut down after about 20 minutes.
During the test, controllers temporarily lost track of both flights they were trying to monitor on the airport's backup radar system: a MedEvac helicopter headed for the Eastern Shore and a US Airways flight that had lifted off from the airport's primary departure runway, according to tower employees.
A story in The Sun on Sunday detailed how the system failed over a two-day period in late August, rendering BWI controllers blind to hundreds of planes, after lightning knocked out the primary ASR-9 radar system and a more sophisticated backup known as CENRAP-Plus.
Air traffic controllers have since filed "unsatisfactory condition" reports to airport tower managers describing the problem and expressing concern that it had been unaddressed.
In a formal response to one of those reports signed Thursday, BWI air traffic manager Don Simons wrote that the CENRAP secondary backup system had been tested weekly since the August incident. Those tests, he wrote, "indicate that CENRAP operates as is designed for a back-up system."
But several tower employees interviewed yesterday said that while it was customary to test the CENRAP-Plus backup system weekly, they couldn't recall any test of the CENRAP system in recent months.
"That was one of the first things we wanted done, and they [tower administrators] wouldn't do it," said Rockton Thurman, president of the local chapter of the National Air Traffic Controllers Association. "I've not been able to locate anybody who can recall the last time CENRAP was tested."
In the late-August incident and on Sunday, the backup system performed far short of accepted standards, said Thurman and tower employees, who requested anonymity for fear of reprisals on the job.
Rex Chase, a tower manager, declined to respond to questions yesterday and referred questions to the Federal Aviation Administration. Other administrators, including Simons, did not return phone messages.
An FAA official maintained yesterday that the system is tested weekly, adding that it performed normally Sunday. "They did not have any failures last Sunday," said spokeswoman Arlene Salac. "It worked the way it's supposed to.
"There is no indication at this point that it's not operating within its normal parameters," she added.
Maryland Transportation Secretary John Porcari contacted officials at FAA headquarters in Washington late Monday to request a personal briefing, said a spokesman for his office.
"He wants to know what occurred during the 27-hour period [in August], and he wants an explanation of the backup procedures and what plans, if any, the FAA has for system improvement in the future," said spokesman Jack Cahalan.
Controllers are accustomed to quirks of the CENRAP system that can render planes invisible for two or three miles. But the failures in late August and on Sunday morning left planes invisible for much longer distances, according to traffic control employees.
Between the evening of Aug. 30 and Aug. 31, more than half the approximately 1,700 flights handled by BWI controllers disappeared from their radar scopes for uncommon lengths of time.
Controllers reported significant blind spots throughout this period. When planes flew into those areas, they disappeared for distances of up to 20 miles. Entire quadrants of the scope went blank at some points. Planes preparing to land at BWI would reach a critical turning point for the final approach and disappear.
In an effort to keep track of the planes dropping off their radar screens, controllers were reduced to trying to keep track of them with notes on paper.
Similar problems surfaced when the same backup radar system was started up for a test at about 6:20 a.m. Sunday morning. Immediately, controllers had trouble identifying a MedEvac helicopter in the air about 10 miles south of Baltimore, according to one air traffic employee.
The helicopter headed for the Eastern Shore was flying at about 1,500 feet, so a controller instructed the pilot to climb higher, to about 2,000 feet. The aircraft remained invisible for five or six minutes, according to sources.
Meanwhile, a US Airways Metro Jet departed from the airport westbound and then immediately failed to appear on the radar scope. Not until the plane was nine miles west of the airport did it pop onto the screen, according to sources.
As a third plane was preparing to take off and while both of the other aircraft were still invisible, a controller plotted a course for the plane that could in no way converge with the other two. But before it left the runway, a decision was made to shut the backup system down.
Such tests typically are conducted early Sunday mornings when traffic is light and there is little possibility of trouble. "Because it was Sunday morning, there really wasn't a safety concern," said one controller. "It just reinforced what we've been trying to get across. This system isn't working right."
With FAA officials denying there is a problem with the system, controllers said they can only speculate that the problem may be with the way the radar data are being fed to Baltimore from the Washington Air Route Traffic Control Center, in Leesburg, Va.