Crj-700 captain reported a near midair collision in the vicinity of dsm.

Attributes
ACN	1566515
Time
Date	201808
Local Time Of Day	1201-1800
Place
Locale Reference	DSM.Airport
State Reference	IA
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	Regional Jet 700 ER/LR (CRJ700)
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Events
Anomaly	Airspace Violation All Types Conflict NMAC Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy
Miss Distance	Vertical 300

Narrative:

ATC gave initial instruction for a descent to an altitude of 11;000 feet by chicago center (I believe); and was given a frequency change right away and minneapolis center (I believe) said amend altitude and maintain FL200. I believe we were crossing FL230; and shortly after; we got a TCAS RA; and we were close to the traffic by about -300 feet. First officer clicked off the autopilot; complied with the RA; and I reported the event to ATC. No further incident.

Original NASA ASRS Text

Title: CRJ-700 Captain reported a NMAC in the vicinity of DSM.

Narrative: ATC gave initial instruction for a descent to an altitude of 11;000 feet by Chicago Center (I believe); and was given a frequency change right away and Minneapolis Center (I believe) said amend altitude and maintain FL200. I believe we were crossing FL230; and shortly after; we got a TCAS RA; and we were close to the traffic by about -300 feet. First Officer clicked off the autopilot; complied with the RA; and I reported the event to ATC. No further incident.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.