Tandemrotor,
In his evidence to the BOI Mr Holbrook gave his position as "2NM SW of the lighthouse". He gave his best estimate of the Chinooks speed as "somewhat faster than Sea Kings in level flight". He later clarified this in his evidence to the Select Committee as "between 60-80 knots". MOD are of the opinion that Sea Kings normally operate at 100-110 knots; so "somewhat faster" could give a speed of approx 130-150 kts which would reflect the known average groundspeed of the aircraft. He also indicated to both the BOI and the HOL Committee that his sighting was limited to a 5 second view. To the FAI, however, he stated that he watched the aircraft for some 25-30 seconds whilst manoeuvring his yacht around some fishing boats.
To the BOI he indicated that he was a solo yachtsman whereas 8 years later to the Select Committee he stated that he called to his "crewman" to come and look at the helicopter. Equally he did not mention the fishing boats in his evidence to the BOI which explains why he was dubbed "the lone yachtsman".
The average groundspeed from the ATC fix on leaving the Aldergrove CTZ to impact was 158 kts. The AAIB concluded that the groundspeed at initial impact was "in the order of 150 knots on a track of approximatey 12 degrees True, and the aircraft was climbing with a flight path approximately 20 degrees above the horizontal." The impact assessment by Boeing gave a groundspeed of 162.8 kts on an aircraft heading of 017 degrees True.
If the evidence of Mr Holbrook is correct then the aircraft would have had to accelerate to a speed well above the average groundspeed of 158 knots to satisfy the known timing constraints of the ATC fix at 16:46:24 and the initial impact power-down time of 16:59:36. With only 2nm to go to the lighthouse this would almost certainly have required exceeding Vne.