Date: 201212
Local time of day: 0601-1200
Location: ZZZZ.Airport, FO
Flight conditions: IMC
Weather elements / visibility: Icing
Light: Dawn
Aircraft: Challenger CL600
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
ATC / advisory: TRACON ZZZZ
Aircraft component: Pneumatic Ducting
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Declared Emergency
Contributing factors: Aircraft; Weather; Company Policy
Primary problem: Aircraft

Narrative: Departed ZZZZ with ground and flight icing conditions. ACARS was only working intermittently; and I had to phone the Dispatcher at the gate for weight and balance information. I could not experiment with different contamination levels; so I had to choose from a limited number of choices. Runway conditions were reported as 70% wet; 20% ice; 10% slush. The runway was clearly contaminated (more than 25% contaminated); so I could not use 'wet'; but I also felt that using 'slippery' was not representative of the actual conditions. I chose 'wet snow; contamination level 1'; just using Captain's judgement to choose something that would represent an equivalent friction level that I thought we would encounter. The performance results indicated Runway XR (the takeoff runway in use) was inadequate; so I called ATC and had them agree to give us Runway XL. After deicing; there was some confusion on how to exit the deice pad; as Ground had changed our runway assignment back to XR. After a call to Ground; they reopened 6L for us; prior to allowing snow removal trucks to clean it. We taxied to XL; and were comfortable that the runway appeared to be what I would estimate as 10% slush on all areas.Takeoff was normal; but climbing through approximately 3;800 FT; we received an 'ANTI-ICE DUCT' warning message; which extinguished on its own after about 30 seconds; and was replaced with 'ANTI-ICE DUCT' caution message. I transferred the radios to the First Officer and followed the QRH; which had me turn off the wing anti-ice; and 'exit icing conditions.' I queried ATC on the tops; and was told FL380. Considering that we were currently in icing conditions (I recall seeing 6 degrees TAT at the time); and there was light to moderate precipitation; I had the First Officer tell ATC we would be returning to ZZZZ. (There was also a pirep on the ATIS concerning moderate icing at 3;000 FT; however we were not accumulating ice at that time). I knew we would be landing significantly overweight (79;483 LBS) on a contaminated runway; but it appeared to be the best option available. We were initially assigned Runway XR; but I asked if XL was available. We were told there would be some delay; so I declared an emergency for priority handling; as I wanted to land on XL. We were descended down to 3;000 for vectors; and fortunately when we reached that altitude the TAT was indicating 14 degrees. I therefore elected to request some delaying vectors; in order to brief the flight attendants; passengers; Dispatcher; and the First Officer on the new approach. Everything went as planned; but I did not get a reply to my ACARS message from the Dispatcher. I assumed it was just due to the spotty ACARS coverage in the area today; and I decided it was more prudent to get on the ground than start looking up radio frequencies; so I used captain's emergency authority and elected to notify the Dispatcher once we returned to the gate.There were multiple threats on this flight.1) I was working on about 5 hours of sleep due to 'reduced rest' of 8 hours 8 minutes; with a very long van ride and clearing customs twice in that time period.2) Our crew arrived 15-20 minutes late at the gate due to hotel transportation issues. (I deadheaded in the previous night by myself; and when I arrived at the hotel; I realized that the van had been scheduled for only 30 minutes prior to duty-in time; which would be clearly inadequate; especially since 1-3 inches of snow and freezing rain that were forecasted. However; because I arrived so late; if I had rescheduled the van I would have interrupted the other crew members' rest in order to notify them; so I was forced to leave the originally scheduled time. Furthermore; one of the flight attendants was 5 minutes late coming downstairs; further adding to the time stress).3) The left pack was deferred; which maxed out our fuel load and did not allow adequate fuel for deicing. I had to call the Dispatcher and remove half the hold fuel to accommodate additional fuel required for deicing.4) Ground control attempted to change runways on us.5) ACARS was not working. I believe I handled the event as well as possible. Better ACARS coverage in ZZZZ would have helped. More guidance from the company on choosing contamination levels might help (especially when it is not clear-cut); although I felt I did as well as I could. We might not have been as overweight if an aircraft with a deferred pack wasn't dispatched all the way to ZZZZ. There would have been much less stress if reduced rest had not been assigned in ZZZZ; or if we had a closer hotel.




Synopsis: CL600 Captain experiences an 'ANTI-ICE DUCT' warning message climbing through 3;800 FT in icing conditions with tops reported at FL380. Reporter elects to return to departure airport for an overweight landing.