ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types
Flight Crew Took Evasive Action
Airspace Structure; Procedure
We were at 10;000 feet and assigned 300 knots; between ESSPO fix and the ORD VOR about 10 to 14 DME and given a turn to 270 degrees. The Captain saw a few TCAS targets pop up and then we got a RA to descend below 10;000 feet. As we had to descend fast we were not able to slow to 250 knots as we went below 10;000 feet. The target aircraft was very close to us; maybe 200 to 400 feet. The Captain called Approach to tell them and they and they forgot to tell us there was a Citation at 10;500 feet. We had descended below 10;000 feet and were off our altitude and were not able to slow to 250 knots below; due to responding to the RA Advisory. That ATC needs to give more warning of aircraft to prevent RA's.
EMB-170 First Officer experiences a TCAS descend RA approaching ORD at 10;000 feet and 300 knots; caused by a Citation at 10;500 feet that ATC forgot to mention.