Vibration
John Blakeley
I was interested to read the article about vibration and thought this might be relevant.
From my time on the civilian Chinook, vibration levels were enormously effected by weight. At MAUW as takeoffs from ABZ invariably were, despite what the graphs said, 115 knots gave a comfortable vibration level whereas 120 knots was uncomfortable and brought complaint from the passengers.
On the return leg when most of the 14,000 lbs of fuel had been burnt, 135-140 knots (the civilian VNO) was usually quite comfortable.
On the flight in question with just over a half load of pax, even with return fuel, it seems unlikely that the aircraft would have been anywhere near MAUW in which case vibration was unlikely to have been a problem.
Perhaps an HC2 pilot could comment.