The track defect that caused last week’s Metro derailment was detected more than a month ago, but it was not repaired, the agency’s top executive said Wednesday.

In addition, the flaw’s detection should have triggered the immediate shutdown of the section of rail involved, but the agency continued to run trains through it until the derailment.

“Let me not mince words: This is unacceptable,” Metro’s interim general manager, Jack Requa, said at a news conference. “It is unacceptable to me, and it should be unacceptable to everyone within the chain of command all the way down to the track laborers and track inspectors who are out on the front lines. We found this and should have addressed it earlier.”

After learning that the rail involved in the Aug. 6 incident should have been fixed after the July inspection, Requa said that he immediately ordered emergency inspections across the system and targeted, enhanced inspections in the immediate area of the derailment to ensure the safety of train operations.

The incident Aug. 6 shut down rail service on parts of three lines for nine hours, leaving thousands of commuters fuming as they scrambled for alternative transportation. The Smithsonian and Federal Triangle Metro stations were closed as crews worked to remove the train and investigators worked to determine a cause.

The derailed cars were not carrying passengers, and no one was injured.

But the agency’s admission that it knew about the defect but failed to act outraged riders and members of the region’s congressional delegation, who have repeatedly hammered Metro for its safety and leadership failings since a January smoke incident that killed one rider and injured more than 80.

“The fact that [the Washington Metropolitan Area Transit Authority] was aware of the track defect that caused last week’s derailment in July yet took no corrective action is more than unacceptable — it is gross negligence that points to a troubling incompetence in the Metro system’s safety practices,” said Rep. Chris Van Hollen (D-Md.). “By sheer luck, last week’s accident did not harm any passengers or Metro employees.

Rep. Gerald E. Connolly (D-Va.) said:“The dysfunction at Metro is now a cancer that is spreading from top to bottom and that has profoundly eroded the public confidence in the ability of Metro to manage itself.”

“Out of Mr. Requa’s own mouth, that is a damning admission of the incompetence that has been allowed to set in throughout the Metro system,” Connolly said.

The defect that caused the derailment, known in rail operations as “wide gauge,” causes a train’s wheels to lose contact with the rails, and is generally the result of old infrastructure. The faulty section of track was found during a routine inspection July 9, using a specialized track geometry vehicle, officials said.

Metro Deputy General Manager Rob Troup said the problem is considered a “code black” defect, which means the track should have been taken out of service immediately.

Metro's interim general manager, Jack Requa, says that the track defect that caused a Metro derailment was detected in July but had not been fixed. (WUSA9)

Requa said he did not know why the agency failed to follow its own procedures.

“The investigation into how and why that occurred continues,” he said. “We are carefully reviewing the individual actions of people, our work processes, and our track policies. . . . When the investigation concludes, we will take all appropriate actions to ensure accountability — from organizational changes to any appropriate personnel actions — and that may include termination.”

The track inspection system in question is the same system senior Metro officials touted as an advanced safety feature that demonstrated the agency’s commitment to improvements when federal investigators were questioning senior executives earlier this summer.

At hearings for the fatal Jan. 12 smoke incident, Metro officials stressed to investigators with the National Transportation Safety Board that safety was a priority for the agency and was tightly monitored and continuously scrutinized, according to transcripts of their interviews.

“That kind of stuff is really good,” said Metro Board Chair Mortimer Downey, describing the work of the special track geometry cars to NTSB investigators. “You’ve got to use it, of course, but it’s really good.”

Troup also lauded the value of the track geometry vehicle to Metro’s safety programs and described a program called Optram in which he said information including details of track inspections are downloaded to enable Metro to “collect data quickly” and assess it to do “targeted maintenance where we need to.”

But identifying the problem and fixing it are two different matters. Wednesday’s news comes on the heels of other examples in which Metro officials identified problems in the system but failed to fix them.

In June, the NTSB said that Metro disregarded its own guidelines and failed to install the proper protective sleeves over power cables in a number of places throughout the system, creating a hazard that could have contributed to the fatal January smoke incident. Yet even after Metro made repairs following the calamity, they did them incorrectly, NTSB officials found.

Many observers blame Metro’s myriad problems on its lack of permanent leadership. The agency has been without a general manager since Richard Sarles retired in January, and efforts to hire a replacement have been hampered by in-fighting among board members. The search was recently restarted with the goal of having a new leader in place by fall. Federal officials have grown so concerned that Transportation Secretary Anthony Foxx recently summoned D.C. Mayor Muriel E. Bowser (D), Maryland Gov. Larry Hogan (R) and Virginia Gov. Terry McAuliffe (D) to his office to discuss Metro’s problems.

Metro’s troubles have drawn scrutiny from a number of federal agencies. In June, using new authority granted to them by Congress, the Federal Transit Administration released a critical review that identified numerous shortcomings in Metro’s safety, maintenance and training programs. Other critical reviews have focused on Metro’s troubled finances. The agency has been forced to take out a series of short-term loans to pay its bills because the FTA has restricted its ability to draw federal funds.

For customers, the Aug. 6 derailment was another in a series of service breakdowns that has many reconsidering whether they will continue to use the system at all. Rail ridership has been declining.

The derailment happened as the train operator was moving the train into position to start morning service at Smithsonian Metro station. Three of the six cars derailed. Requa said Wednesday that there was no operator error or equipment malfunction involved.

Metro officials were able to restore partial rail service later that evening and reopened the stations, but efforts to return full service to the lines Friday morning were thwarted after an early morning power outage forced them to halt service on the western end of the lines between the East Falls Church and West Falls Church Metro stations and between the East Falls Church and McLean Metro stations. Nearly 100 people aboard a Silver Line train at East Falls Church had to be evacuated from a tunnel.

In a rare move, Metro officials offered refunds to SmarTrip users who used the system Friday.

The service breakdown was the second major problem on the Blue, Orange and Silver lines since May, when an electrical malfunction created smoky conditions in a tunnel between the Rosslyn and Court House Metro stations. That led to an hours-long service disruption during the peak of the morning commute.

Mary Pat Flaherty and Luz Lazo contributed to this report.