Circuit at Metro Crash Site Began Malfunctioning in Late '07, NTSB Says
Friday, July 24, 2009
The track circuit at the center of last month's deadly Red Line crash has been intermittently malfunctioning for the past 18 months, when a key piece of equipment was replaced by Metro crews, federal safety investigators said Thursday.
According to the National Transportation Safety Board, the track circuit at the crash site has functioned irregularly since December 2007. Its performance deteriorated further five days before the June 22 crash, when it apparently failed to detect the presence of a train outside the Fort Totten Station, permitting another to plow into it. Nine people were killed, and 80 were injured.
The new information from the NTSB suggests that as long as 18 months ago, Metro officials could have found defects in the track circuitry where the accident occurred. Metro officials said Thursday that they did not know the circuit had been intermittently malfunctioning because they did not conduct tests that would reveal that specific problem.
Metro General Manager John B. Catoe Jr. likened the different level of analysis to a blood test. "When you have blood drawn, you can ask for test A through 25," he said. "We were only doing test one."
Investigators have not determined whether knowledge of the earlier problems could have prevented the crash. Asked about it Thursday, Catoe said: "Not that we're aware of. . . . I don't want to speculate on anything until I have the facts."
Investigators are reviewing maintenance records and operations records to see whether technicians, operators or anyone else reported problems with the circuit at the heart of the investigation, whether Metro officials were aware it was not functioning properly and what, if any, action was taken.
Asked whether managers had received reports from Metro employees about problems with that circuit since December 2007, Catoe said he and his staff were not aware of any such reports.
Federal investigators found that the circuit began "fluttering," or intermittently malfunctioning, after Metro crews installed a device known as an impedance bond, also called a Wee-Z bond, at the circuit in December 2007, according to a safety board advisory issued Thursday. Metro has been installing new bonds across the 106-mile railroad as part of a project to boost power so the agency can run more eight-car trains, which consume more electricity than shorter trains. Each track circuit has two Wee-Z bonds.
The fluttering indicated a problem with the circuit, according to the data examined by the NTSB. After Metro crews replaced the second Wee-Z bond in the same circuit June 17, the circuit deteriorated to the most dangerous stage: It intermittently failed to detect the presence of a train. Five days later, a train idling in that circuit outside the Fort Totten Station was hit from behind by another train.
It is unclear what caused the circuit to malfunction. The NTSB has not determined the root cause of the crash.
Since the crash, Metro officials have replaced components in the track circuit, and it continues to malfunction. Federal investigators are now also looking at possible sources of interference, including electromagnetic interference, in the area of the circuit.
In the month since the crash, Metro officials have gone back to more closely examine their track circuit data. Typically, Metro samples track circuit data each month and looks only for the most severe condition: a track circuit that fails to detect the presence of a train.