WASHINGTON — When Christopher A. Hart, the chairman of the National Transportation Safety Board, appeared before a congressional panel this week to discuss the investigation into last month’s deadly Amtrak derailment in Philadelphia, lawmakers wanted to know one thing: Was the train’s engineer using his phone at the time of the accident?  “Could you just tell us again in plain English why we don’t know if this operator was on the phone three weeks after the accident?” said Representative Sean Patrick Maloney, Democrat of New York and a member of the House Transportation and Infrastructure Committee, echoing questions raised by other members of the panel.  It seemed like a straightforward question, but it was one the federal regulator had trouble answering.  The engineer, Brandon Bostian, has given regulators the password to the phone and the agency has access to its data from his carrier, Mr. Hart said. But the investigation has been slowed because of the way the phone carrier stores that data. For example, the voice calls on Mr. Bostian’s phone were in one time zone, while the texts were in another, he said.  “And we found discrepancies within the carrier’s own time system where it didn’t even agree with itself,” he said. “So we have a lot to work out that is far more complicated than we anticipated.”  Cellphone records are often used as evidence in crash investigations, tracing which cell tower was used to make or receive a call or text, and determining when a phone was in use. But experts say that despite the perception that getting the information is simply a matter of looking through call logs, it is a much more involved process. In the past, the complexities have caused the transportation safety board to wrongfully conclude that a cellphone was in use at the time of an accident.  “Cellphone technology and how networks work is complicated so you can’t just go in and grab some records and say what happened,” said Michael Cherry, a former Bell Labs and NASA consultant in Virginia, who has testified in court cases involving the use of cellphone records by law enforcement.  At the heart of the issue is the way cellphone data and calls are routed across a carrier’s network. To keep cell towers in one area from being overloaded by calls, data and text, cellphones do not always use the tower that is closest to the caller. Instead calls are routed by a computerized switching center — a hub for cell sites that are usually grouped geographically — to the tower that best helps the phone network balance the traffic.  For instance, if a call is placed in Washington, D.C., it may be handled by a switching center in Atlanta and the cellphone record will show the time zone of the call as being the same as the cell tower at that location.  Most railroads are expected to miss the deadline to install automatic speed control systems by the end of this year.  But the very next call may come at a time when the Atlanta switch is crowded, so that call could be handled by a switch in Southern California and be stamped as Pacific time. The process works the same for text and other phone data, experts say.  The safety board said it was working with Mr. Bostian’s carrier to try to unscramble the time zones.  “It’s one thing to see if a text message was sent or a phone call was made,” said Peter C. Knudson, a spokesman for the safety board. “And it’s another to determine if any data was being used by an app on the phone.”  Mr. Knudson said there was still another process to go through to see whether a phone was manipulated by the user or if the data use was just part of the normal data exchange from the phone to the cellular provider.  Mr. Bostian, the engineer, has told investigators that the phone was in his bag. Although the records appear to indicate that calls and text messages were sent and received on the day of the accident, investigators have not yet determined if the phone was used while he was operating the train.  Witnesses described the scene after a New York-bound Amtrak train derailed and overturned late Tuesday in Philadelphia, leaving some passengers dead.  Investigators say they have started the process of correlating the time stamps in Mr. Bostian’s cellphone records with multiple data sources, including the train’s event recorder and its outward facing video, along with recorded radio communications and surveillance video.  This is not the first time the safety board has had problems with using cellphone data.  In 2009, investigators from the agency admitted that they were mistaken when they claimed that a Coast Guard crew member had sent text messages just before his boat collided with another vessel and killed an 8-year-old boy before a holiday boat parade in San Diego Bay.  In its initial report, the safety board said the Coast Guard crewman had sent and received as many as six text messages just minutes before the collision on Dec. 20, 2009.  But the agency later revised its report because records from Sprint listed the cellphone calls in Pacific Standard Time but the time zone for the text messages was unclear — it was either Central or Eastern time. . The agency has never been able to accurately determine when the messages were sent.  Despite the issues, officials said they would eventually be able to determine if the phone was in use before the accident in Philadelphia.  “Getting definitive answers to these questions is a highly detailed and technical process and we’ve got to make sure that we get it right,” Mr. Knudson said.
The way data is stored has made tracking the phone use of the engineer in last month’s derailment in Philadelphia more complicated than investigators expected.