Loose bolts were found to be at least one common thread between the sudden separation of two Metro trains over the past two months, the agency that oversees Metrorail safety said Wednesday.
On Oct. 9, two rail cars separated on a Red Line train outside Union Station, stranding 108 passengers for nearly two hours. Metro inspected the hitching apparatuses for its fleet of 6000-series trains, pulling six for further examination.
Three cars were found to have incorrect hardware, according to Metro. The rest were put back into service.
On Nov. 24, another Red Line train, this time carrying 12 passengers between the Wheaton and Glenmont stations in Montgomery County, separated between the fourth and fifth cars. No one was injured, but Metro suspended the use of nearly 180 of its 6000-series rail cars while investigators look into possible causes and links between the incidents.
The 6000-series is Metro’s second-newest model within its fleet of nearly 1,200 rail cars. The series is about 14 years old — approaching the 20-year “midlife” mark, when Metro rail cars are typically put through a thorough overhaul.
Both separations occurred at the trains’ couplers — the large latches at the end of each rail car that connect to adjoining cars.
The Washington Metrorail Safety Commission, an independent agency created by Congress two years ago, determined that five bolts were loose on top of the coupler assembly of one of the cars involved in the Nov. 24 separation, identified as Car No. 6177.
Four of the bolts were intended to hold a guide rail in place to prevent the coupler assembly from rotating, while a fifth was identified as a “clamping bolt,” the safety commission said in a statement.
“Screw-like threads” were found to be worn, damaged or flattened, while corrosion and contaminants were found on other threads within the inspected coupler assembly, the agency said.
Parts of the coupler were included in Metro’s emergency inspection of 6000-series cars after the Oct. 9 incident, the safety commission said. Officials are investigating whether the same issues were documented during the most recent inspection or if they should have been found.
The safety commission said it’s also unclear whether some of the same parts were examined during a regular maintenance check on Oct. 21.
While both rail car incidents occurred in coupler assemblies, safety commission officials also found after the Oct. 9 separation that a gland nut was not properly torqued. The nut is in a different part of the coupler assembly than the loose bolts found in the latest uncoupling incident.
Metro and the safety commission have enlisted the help of Alstom, a French multinational company that built the 6000-series cars. Their investigations are expected to last a few more weeks.
The investigation into the Oct. 9 separation came under greater scrutiny when Metro was found to have failed to secure evidence from the separation, mistakenly allowing a work crew to test bolts on the failed coupler without permission or supervision from the safety commission. No such compromising of evidence occurred with the most recent incident, the commission said.
“Metro personnel followed the proper chain of custody procedures prior to this week’s reviews of the couplers involved in the Nov. 24 pull-apart,” the commission’s statement said.
Metro spokesman Ian Jannetta had no comment on the safety commission’s Wednesday report. He said 6000-series trains remain out of service indefinitely.
“Metro’s investigation is ongoing and we don’t have an interim update to offer at this stage,” he said.