Date: 201304
Local time of day: 0601-1200
Location: ZZZ.TRACON, US
Flight conditions: IMC
Weather elements / visibility: Icing
Aircraft: Dash 8-400
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Climb
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Pressurization Control System
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution; Flight Crew Overcame Equipment Problem
Contributing factors: Human Factors; Procedure; Weather; Aircraft
Primary problem: Human Factors

Narrative: While monitoring a Prop Anti-Ice abnormality; a CABIN PRESS Warning message came into the advisory board. The altitude was through 10;000 FT to 11;000 FT assigned. At that time we immediately asked ATC for stop climb and return to a maximum of 10;000 feet for the time being.  Since we were in icing condition; IMC; I decided to not run the QRH for CABIN PRESS and stick to the basics of flying the airplane; navigating and then communicating. Because of the previous problem with the Prop Anti-Ice it was more important to me to get out of icing conditions and land as soon as possible than to run the QRH. While conducting the Immediate Return Checklist I found that Maintenance had moved the pressurization selection switch to 'dump' while performing a check on the Prop Anti-Ice on the ground. It was selected to 'Auto' and at that point I informed the FO that the problem was the switch. After the selection I monitored the Cabin Press and it normalized. At that point I continued with the preparations to land the airplane. Once the airplane was set up for landing we told ATC that we were ready for landing. We never declared an emergency since the airplane was never in a position were the final outcome was in doubt. I did declare an urgency situation in which I wasn't willing to be flying around [Class B] Airspace for too long. While Maintenance was conducting its checks on the ground I was on the airplane with them. Because of this I never checked the position of the Pressurization Selector since I had setup the airplane for departure and I had brought it in. 1. As PIC Redo a full Acceptance Check and Set-up after Maintenance has been on the airplane. 2. Maintenance needs to reposition switches that need to be and remain in the Auto position after performing checks on the airplane.




Synopsis: Q400 Captain experiences a CABIN PRESS Warning passing 10;000 feet while monitoring a Prop Anti-Ice abnormality. During preparations for return it is discovered that Maintenance had moved the pressurization selection switch to 'dump' while performing a check on the Prop Anti-Ice on the ground. The switch is returned to Automatic but the crew elects to return for the propeller anti ice anomaly.