Icing was not a factor in the accident but chatting about it was.
NTSB scrutinizes pilots in Colgan Q400 crash probe: AINonline
NTSB hearing officer Lorenda Ward reported that the crew engaged in non-essential conversation while flying below 10,000 feet in violation of FAA rules, including, for example, a three-minute discussion on the first officer’s experience in icing conditions and training. “This conversation occurred just a few minutes before the stick shaker activated and while the crew was executing the approach checklist,” said Ward.
Although the pilots reported ice accretion on the airplane’s windshield and wings, airplane performance modeling and simulation conducted by the NTSB show that icing had “minimal effect” on the stall speed of the airplane. Information from the airplane’s FDR indicates that the stick shaker activated at 130 knots, a speed consistent with an engaged de-icing system. FDR data further indicates that when the stick shaker activated, the control column experienced a 25-pound pull force, followed by an up elevator deflection and an increase in pitch, angle of attack and g forces.
During the flight’s climb to 16,000 feet, the crew activated the de-icing systems and left them on throughout the flight. About 40 minutes into the flight, the crew began their descent and at 10:10 p.m. they discussed the build-up of ice on the windshield. At 10:12, the flight received clearance to descend to 2,300 feet and reached that altitude at 10:14. At 10:16 the crew lowered the landing gear, and about 20 seconds later the first officer moved the flaps from 5 to 10 degrees. The stick shaker activated and the autopilot disengaged shortly thereafter. The crew added power to about 75-percent torque and the control column moved aft. That accompanied a pitch-up motion, a left roll, followed by a right roll, during which time the stick pusher activated and the flaps retracted. The airspeed then decreased and after further pitch and roll excursions the airplane pitched down and entered a steep descent from which it did not recover.