Brian,
Perhaps the reason that people give less credence to the evidence of Mr Holbrook is that the evidence he gave to the FAI (and the HOL Commitee) was markedly different to that he gave to the BOI in the immediate aftermath of the Accident. Both accounts were given on oath.
Of course, by the time the FAI sat the BOI (which had been given to Next of Kin on an "In Confidence" basis) had been leaked to the Press.
I undestand the he stated that he changed his opinion of the height and speed of the Chinook after watching Sea King's on approach at Prestwick some months later.