All this discussion about times to V1 and assessing whether the take off is proceeding normally is all very interesting. BUT, the problem is that it’s very subjective.
Risk management design just doesn’t allow this type of guesswork into such critical phases of flight.
We need to come back to the take off data as designed by the manufacturer and certified by state authorities as the reference performance document .
Data is accessed on every take off, whether it’s via tables or laptop and, (unfortunately) relies on human input to obtain correct figures. If the crew, on the day, make an error in the input data, then they’ve made an error and wear the consequences (aircraft loss, damage, injury etc) as seen in numerous incidents and accidents with varying outcomes.
This error though, is the end result only. In most take off events such as this, there are generally systemic issues that prevented error trapping at multiple points during the pre flight, start, taxy stages of the flight, before the aircraft has even lined up on the runway.
We have to accept that it’s “normal” for all of us to make errors. That’s why we design processes that supposedly mitigate against the types of errors we are talking about.
Design of error management and trapping processes and procedures is the responsibility of management, not the responsibility of line pilots. Crews should follow these SOP’S with the reasonable expectation that they contain appropriate traps to prevent that final error.
If crews choose deliberately ignore SOP’s, then, yes, they have to accept responsibility.
But, if the process itself is flawed, then it’s senior management who must accept most of this responsibility.
Sadly, history has proved that flight crews are often the scapegoats for senior management shortcomings. This event will probably be no different.