Sanchez was driving Metrolink 111 when it collided with another train in the Los Angeles suburb of Chatsworth on Sept. 12, killing 25 people and injuring more than 130 others.
"On the day of the accident, the Metrolink engineer was on duty for two periods of time," the NTSB advisory states. "The engineer was responsible for the operation of a train from 6:44 a.m. until 8:53 a.m. During this period of time, the engineer's cell phone received 21 text messages and sent 24 text messages."
Sanchez was then off-duty until 2 p.m. and was responsible for the operation of Metrolink 111 from 3:03 p.m. until the accident occurred. Records indicate that Sanchez's cell phone received seven text messages and sent five text messages during this time.
The NTSB says that cell phone records show that that last text message received by the engineer's phone before the accident was at 4:21:03 p.m. and that the last text message sent was at 4:22:01 p.m.
According to the data recorder of the Union Pacific train that collided with the Metrolink train, the crash occurred at 4:22:23 p.m.
The NTSB said that while the precise timing of these events is still under investigation, "preliminary information is being released regarding the approximate cell phone activity during the engineer's duty hours on the day of the accident."
Acting NTSB Chairman Mark V. Rosenker said in a statement that he's pleased with the progress of this investigation so far and that the NTSB continues to investigate the accident and to explore ways to prevent similar incidents in the future.
Last week, California Gov. Arnold Schwarzenegger signed a bill that outlaws the use of text messaging devices while operating a motor vehicle.
On Sept. 18, the California Public Utilities Commission "prohibited the personal use of commercial mobile radio services and devices by on-duty railroad engineers, brakemen, conductors, or rail transit vehicle operators except for personal communications that take place when the train or transit vehicle is stopped and with the approval of the appropriate management personnel."
The commission expects to consider whether or not to make this ban permanent.