Member Robert L. Sumwalt III filed the following concurring statement on May 20, 2016.
In the Board Meeting, there was an interesting discussion about whether the lack of Positive Train Control (PTC) should have been included in the causal statement of the Probable Cause, or whether it should be listed as a contributing factor. The majority, including me, decided in a 3 to 1 vote that the lack of PTC should be cited as a contributing factor.
In order for something to be listed as a causal factor, in my opinion, it must be an event, failure, or circumstance that initiated the accident sequence. To say the lack of PTC initiated the tragic Amtrak 188 accident sequence would be equivalent to saying that the cause of a tightrope walker's fatal plunge was the lack of a safety net below him. When it comes to railroad safety, that's precisely what PTC is —a safety net to trap errors, not by a tightrope walker in this case, but by a locomotive engineer.
That said, it's important to note that I do not believe only human errors committed by front line employees should be listed in the causal statement, or that issues such as organizational factors or lack of regulatory oversight should be relegated to contributing factors. To the contrary, there have been several accidents where I have pushed to have these factors listed in the causal statement. For example, last year the Board deliberated a commercial spaceship accident where the copilot actuated a lever prematurely, resulting in the inflight breakup of the vehicle. The Probable Cause proposed by staff listed the copilot's error in the causal statement, followed by a contributing factor of the spaceship manufacturer's failure to consider and protect against the possibility that a single human error could be catastrophic. I argued that if the spaceship manufacturer had designed a system that would not have allowed the copilot's error to occur, this accident would not have happened. Therefore, I felt the manufacturer's failure should be moved from a contributing factor to the causal statement. My colleagues agreed.
There is a subtle, but important, distinction between the commercial spaceship and Amtrak 188 cases. In the spaceship crash, the organization's failure to properly design the spaceship set the stage for the copilot's error. In short, it enabled the error. In the case of Amtrak 188, the lack of PTC did not enable the locomotive engineer's error. While its presence might have prevented his error from becoming catastrophic, the lack of PTC did not set the stage for his error of entering the Frankford Junction curve at excessive speed.
The Board unanimously adopted a finding that states, in part, "a fully implemented positive train control system would have prevented the accident." However, one must not confuse prevention with causation.
In the Board Meeting, it was suggested that by elevating PTC into the main body of the causal statement, it would help send the message that the NTSB strongly believes in the importance of PTC. While I agree a well-crafted Probable Cause statement can be useful in sending a powerful message, it must be underpinned by logic and supported by evidence. A Probable Cause statement that lacks either element potentially undermines the credibility of NTSB investigations.
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