The National Transportation Safety Board is still examining the cellphone of the engineer involved in a deadly Amtrak accident last month, but as the agency tries to determine the cause of the deadly crash it has concluded that the driver wasn’t talking or texting at the time.

“We have determined that there was no talking or texting or data usage involved,” said NTSB Vice Chairman T. Bella Dinh-Zarr, who testified recently before a Senate Commerce, Science and Transportation Committee hearing on passenger rail safety.

But Dinh-Zarr left room for other types of use.

“There are 400,000 pieces of data involved in the analysis, and because of the extent of that, things like use of an app or other use of the phone has not been determined,” she said.

The NTSB said it still doesn’t know whether the phone was turned off or in airplane mode, which allows the phone to remain on but not transmit data. Cellphone users can access applications on the phone such as games or music in such a mode.

Federal Railroad Administration regulations require the engineer’s personal cellphone to be turned off.

Another complication has to do with multiple systems used by the cellphone carrier to log activity, which cross several time zones. The NTSB said investigators are obtaining a cellphone identical to the engineer’s and will be running tests to validate the original data.