A final report could come in a year's time, NTSB officials said. No doubt many things may have contributed to this derailment, in which a Blue Line train jumped the tracks and climbed up an elevator at the O'Hare International Airport station.
On Wednesday, officials released more information on the operator of Blue Line run 141. She started with the CTA less than a year ago and has been operating trains for just 60 days. The operator is a member of the extra board, which means she's called in to fill in on the needed shifts.
The operator admitted to investigators that she fell asleep at the controls during the early morning run on Monday, March 24, and woke just as the train crashed. She also said in February she missed a station because she dozed off at the controls. She was admonished by her supervisor, but it's unclear if there was other discipline.
"Recently, prior to this accident, she also stated that she overslept and was late for work. And we are now comparing all of CTA's documentations as far as discipline records, time on and off duty and comparing that to the schedules she gave us during the interview," NTSB lead investigator Ted Turpin said.
In the summer of 2001, there were two CTA train accidents in less than two months. In their aftermath, the NTSB raised concerns about operator training and oversight.
One of the operators back then had twice failed to qualify before later being cleared to run a train. She then accumulated "excessive safety violations", was retrained, and a month later crashed her train into another.
Then, the safety board concluded CTA oversight of rail operating rules was "inadequate in design and execution."
While the CTA did initiate changes, Monday's derailment will again look at safety oversight. One of NTSB's interviews was with the CTA's lead trainer.
"We got an in-depth detailed of how operators are trained and how the training process that CTA uses to prepare operators to run their trains," Turpin said.
As was the case after the previous accidents, the NTSB will offer a big picture when it releases its probable cause report.
On Wednesday, the CTA said that in the February incident, the CTA operator said only that she "closed her eyes for the moment" and only one car passed the station.
The CTA is also going to lower the speed limit for trains entering the O'Hare train station from 25 to 15 miles per hour and re-position the trip arms that are meant to brake the trains during emergencies.