Embraer Jet Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Procedure
We were on the WATSN 3 Arrival headed into ORD. We were given a clearance to cross HULLS at 12;000'. We descended and were about 10 miles south of HULLS when we leveled off at 12000'. At around the same time; ATC issued a traffic advisory to us and a Citation that was at our 2 o'clock and approximately 7 miles. We both called each other in sight; and then ATC asked the Citation if he could maintain visual separation and climb through our altitude. At this point; the Citation said 'yes' and started a climb. We immediately got a TA; followed by a Resolution Advisory (RA). We climbed per the TCAS instructions to about 12;900'; and then descended back down to our assigned altitude of 12;000'. We looked at our TCAS at 12;900'; and the Citation was less than a mile behind us; -800 below us. The First Officer could see the Citation right outside the window; and could tell he was slightly behind us.I don't think we were ever in immediate danger; but feel as if the visual climb was a pretty odd clearance in such close proximity to an arriving aircraft.The Controller's response to our climb was '[The Citation] had a clearance to climb through your altitude maintaining visual separation.'The [Citation's] response was 'we weren't close at all.'Our TCAS said we were close enough.Although we had the aircraft in sight; we elected to follow the TCAS RA guidance for two reasons. 1) Because that's what we are trained to do. 2) The way the Citation was heading towards us; it was very difficult to see which way the airplane was moving; as it was coming right for us.
Regional Jet Captain reported responding to a TCAS RA climb command while descending into ORD when a Citation climbing VFR triggered the conflict alert.