B737NG flight crew reported that while descending into las they received and responded to an RA with...

Attributes
ACN	1416876
Time
Date	201701
Local Time Of Day	1201-1800
Place
Locale Reference	LAS.Airport
State Reference	NV
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	STAR KEPEC3
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	Climb
Person 1
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 161 Flight Crew Type 161
Person 2
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 201 Flight Crew Type 8500
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict

Narrative:

Descending into las in the vicinity or ipumy fix; we received a 'traffic; traffic' TCAS TA warning. The associated traffic showed 3500 feet below our current altitude and climbing. Neither captain nor I could visually acquire the traffic. Sometime later we received a 'climb' RA and the captain disconnected the autopilot and complied with the RA. During this time I visually acquired the aircraft in question passing our 3 o'clock at a distance I would assess between 1/2 mile to a mile slightly below our altitude and by the time it reached my 4 o'clock it was co-altitude and still climbing. The radios were busy and I couldn't get an advisory call to ATC yet. At this point the RA audibly gave another command I believe was 'monitor vertical speed' quickly followed by clear of conflict. At this point we told ATC of our maneuver and they responded that aircraft had violated their clearance and wasn't answering. I assume they were on a different approach/departure frequency than we were. We were given a new descent clearance; the captain reengaged the autopilot; and the flight proceeded uneventfully the rest of the way to the gate.we were never advised by ATC of the conflict due to multiple frequencies and congestion on the radios. I also am unaware of the assigned altitude that the other aircraft violated; but altitude closures happen quickly when one is descending in idle; and another is climbing at climb thrust! TCAS worked as advertised.

Original NASA ASRS Text

Title: B737NG flight crew reported that while descending into LAS they received and responded to an RA with a climbing resolution. Shortly after; ATC came on to advise them the other aircraft overshot their altitude causing the conflict.

Narrative: Descending into LAS in the vicinity or IPUMY fix; we received a 'traffic; traffic' TCAS TA warning. The associated traffic showed 3500 feet below our current altitude and climbing. Neither Captain nor I could visually acquire the traffic. Sometime later we received a 'Climb' RA and the Captain disconnected the autopilot and complied with the RA. During this time I visually acquired the aircraft in question passing our 3 o'clock at a distance I would assess between 1/2 mile to a mile slightly below our altitude and by the time it reached my 4 o'clock it was co-altitude and still climbing. The radios were busy and I couldn't get an advisory call to ATC yet. At this point the RA audibly gave another command I believe was 'monitor Vertical Speed' quickly followed by clear of conflict. At this point we told ATC of our maneuver and they responded that aircraft had violated their clearance and wasn't answering. I assume they were on a different Approach/Departure frequency than we were. We were given a new descent clearance; the Captain reengaged the autopilot; and the flight proceeded uneventfully the rest of the way to the gate.We were never advised by ATC of the conflict due to multiple frequencies and congestion on the radios. I also am unaware of the assigned altitude that the other aircraft violated; but altitude closures happen quickly when one is descending in idle; and another is climbing at climb thrust! TCAS worked as advertised.

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.

B737NG flight crew reported that while descending into las they received and responded to an RA with a climbing resolution. Shortly after; ATC came on to advise them the other aircraft overshot their altitude causing the conflict.