Here's some clarification on what exactly is meant by the warning in the AFM. To save you the time of scrolling back to the original thread I'll post the warning below:
"WARNING: Severe icing may result from environmental conditions outside of those for which the airplane is certificated. Flight in freezing rain, freezing drizle, or mixed icing conditions (supercooled liquid water and ice crystals) may result in ice build-up on protected surfaces exceeding the capability of the ice protection system, or may result in ice forming aft of the protected surfaces. This ice may not be shed using the ice protection sytems, and may seriously degrade the performance and controllability of the airplane."
The above warning is required by an AD as a result of the ATR that crashed in Roselawn, IN. It's required for all aircraft with deicing boots and unpowered controls.
The head of Skyway's safety department did some research and found some information that sheds light as to what the FAA's intent was with this warning. Here's the link:
http://www.airweb.faa.gov/Regulator...CE4EBD1269CF04AC86256A22006FECBF?OpenDocument
Comment #4 contains this wording: "These AD's do not prohibit flight into forecast or reported freezing rain or freezing drizzle. This means that the aircraft is not prohibited from takeoff, dispatch, or release simply because the forecast may indicate freezing rain or freezing drizzle, but is prohibited from continued flight in severe icing conditions."
The purpose of the AD (and the warning that it requires) is not to prevent flight into freezing rain/drizzle but to give pilots clear warning signs of when they are in severe icing conditions (the warning continues to list these warning signs - ice buildup aft of protected surfaces, ice buildup on side windows, etc). Before this warning came out, pilots may have seen ice on the side window and not recognize that this was a warning that ice is also accumulating aft of protected surfaces.
If I had been aware of that I would have flown the airplane into -FZRA with a clear conscience and not felt that I was taking an unreasonable risk with my passnegers' lives.
However, there's a fly in the ointment. Remember the e-mail I got from Dornier, the one that said, "Takeoff into freezing rain, including light freezing rain is not permitted"? Now, despite the fact that the AD doesn't prevent takeoff (or landing) into known freezing rain, the Type Certificate Holder says we can't do it! Now what???
Skyway sent a VERY pointed e-mail to Dornier 328 Support Services essentially demanding that they retract that statement immediately. Dornier's response: "If there is evidence of freezing drizzle and freezing rain (= severe icing conditions) a take off/flight is prohibited."
I'll admit that, after reading the FAA's intent with the AD, I'm a bit puzzled as to why Dornier is so adamant about not flying the 328 into FZRA. Nonetheless, the fact remains that they clearly say, "Y'all better not go there!".