We’re now into day two of the NTSB’s public hearing on the deadly June 22 Red Line crash (you can watch the hearing live online), and while the safety board has yet to release its formal conclusions on the cause of the accident, hundreds of pages of documents released to the public on Tuesday provide details on their findings.

Investigators found that several days before the crash, a work order (above) was issued to repair a “bobbing” track circuit at the very spot where the crash later occurred, on the Red Line tracks near the Ft. Totten station. The NTSB report defines a bobbing track circuit as when “an isolated track circuit transitions from vacant, to occupied and back to vacant again.” A maintenance crew had first reported the bobbing circuit on June 17, and a subsequent crew performing a regularly scheduled preventive maintenance inspection on June 18 encountered the same problem, but no fix was applied at that time due to a thunderstorm:

When their testing was complete, they noticed that track circuit B2-304 was bobbing. They stated that no adjustments were made since the weather was turning bad and the track circuit had just been verified with the shunt test. The ATC mechanics stated that they did not report that track circuit B2-304 was bobbing to MOC because the problem cleared itself while they were troubleshooting. The ATC mechanics stated they were not aware of the open work order regarding track circuit B2-304.

The work order that had been opened on June 17 remained open until the day of the accident, according to the NTSB. They also found that the same track circuit, B2-304, had been reported to have been bobbing back in February 2008, and that work order had not been closed until September of that year. Entries on that work order “did not contain any information concerning remedial action taken to correct the bobbing track circuit.”