I flew Beech 1900's for the USAF. While I was there, an air directive came out about tail icing. I believe this was in response to the ATR crash that was holding for approach in Chicago. There was also a video we watched from the FAA which was created by NASA.

Essentially what TZADIK posted is spot on. For T-Tail aircraft, due to the flow of air over the wing which effects the flow of air over the T-Tail, this can lead to significant ice build up on the T-Tail. In fact, if you see a little ice on the wings or cockpit, you already have TOO MUCH ice on the tail. NASA showed video of the wing and T-Tail of a plane that was flown into heavy icing. Even though the wing had maybe an inch of ice on the leading edge, the tail had 4 times as much! They also showed recovery techniques which are the same as given above and are opposite for a normal wing stall recovery.

This air directive changed how often and when to blow the boots on the Beech 1900 and the procedure was changed in our manuals.

I have to admit, I am kind of surprised that this is something new for the guys who are flying T-tails. If you don't know it.

-Fatty