The preliminary NTSB report, as usual, raises more questions than answers. The last sentence in the report raises the most salient questions. Like everyone else, I can only speculate as to the root causes until the final report is released. I have two general questions not directly related to the investigation that an engineer should be able to answer. 1) Does the engineer have any way to know if the FRED is mechanically malfunctioning, i.e, communicating, but for some reason not responding to a command to plug the air? 2) Does the engineer have a prominently placed gauge or instrument to continuously monitor the CFM flow to the train line, or is this information only available in the event recorder?
The answers to these questions doesn't necessarily answer the question as to the root cause of the accident, but raises the level of speculation to a higher level. Like everyone else, I admit to a natural instinct to speculate until all the facts are revealed.