It is a weird accident.
The aircraft fell 2.200 feet in a matter of seconds, and the pilots appeared to have lost control.
From pictures of the wreckage you can see, that the aircraft did plunge to the ground in a vertical position. The tail is in pretty intact condition, and eye witnesses reports of a 20-25 degrees nose down attitude. The pilots may have been recovering from, whatever upset attitude, they were in - but eventually ran out of altitude.
The question of icing springs into mind, since icing have caused several accidents involving turboprop aircraft. This might have been the case, but the ice protection system of the Q400 is very conservative - due to the Roselawn accident. Furthermore, the aircraft had not been holding or asked to reduce speed, while approaching the airport.
The Q400 has an ice detector, that will sense any ice, and you have spigots on the wind shield wipers, where the pilots can ciearly see ice building up. If the pilot get ice detection caution/warning, he pilot should immediately apply wing de icing, and turn on the "increase ref." switch that will increase the stall floor with 20 knots. You should then increase any bug speeds with 20 knots. From what I have heard, that will allow the aircraft to carry 3 inches of ice on the wing tips - and still be safe.
The check lists calls for immediate application of wing anti ice, when detecting ice. You should not wait for half an inch of ice. Recent NASA studies have disclosed, that ice "bridging" are not likely to occur under any condition. Ice bridging is a myth.
In case any of the boots does not inflate properly, the pilot will have "de ice pressure" caution. Cycling the wing de icing system, you can detect what boot is causing proplems. In case of a pressure leak in the boot system, you can split the system, but this requires you to exit icing conditions immediately, since you wiil have asymmetric wing de icing.
Therefor, if icing plays a part in this accident, it propably also involves faulty use of the ice protection system.
Best regards
SE210
PS - If you have the "increase ref" switch on and forget to ad 20 knots to the bug speeds - then you will stall at a speed, that is 20 knots higher than normal. This might be an issue to look into as well.