Dash 8-200
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types
Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Human Factors; Airspace Structure; Procedure
While in cruise; we noticed an airplane on TCAS several miles ahead of us and 2400 feet below us in a climb. We watched the airplane continue to climb directly ahead of us at our 12 o'clock position. Figuring the airplane would level out 1000 below us; we continued on course but kept a vigilant eye on the traffic. Immediately once the traffic passed through 1000 feet below us in a steady climb; we queried Approach about traffic at our 12 o'clock and a mile or two and climbing. Once the traffic hit 400 feet below us and directly ahead of us; I didn't wait for ATC to respond but immediately turned off the autopilot and advised ATC we were making an immediate turn to the west. During ATC's then notification of the traffic; we received a TCAS RA with a 2000 feet per minute climb. We complied with the RA; and the traffic passed directly below us at 500 feet separation until we received the 'Clear of Conflict' notification.Being given notice of the traffic earlier (or at any time) by ATC certainly would have helped. The next controller let us know that the traffic appeared to have just departed Danbury and climbed right through our altitude; so maybe the controllers were not anticipating this traffic? TCAS and monitoring our instruments certainly came through for us.
DHC8 Captain at cruise altitude experienced an airborne conflict with another aircraft climbing into their altitude. The reporter initiated a turn at about the same time ATC called the traffic and TCAS annunciated a climb RA.