B737 ng flight crew reported that they had a near miss while intercepting the localizer on approach.

Attributes
ACN	1519729
Time
Date	201802
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	Climb
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument
Events
Anomaly	Conflict NMAC Deviation - Altitude Excursion From Assigned Altitude
Miss Distance	Vertical 200

Narrative:

We had a near miss on approach! Flying a westerly heading the approach controller told us to 'turn right 010; intercept the localizer; descend maintain 3;000 feet until established cleared ILS'. In our turn and descending; the approach controller came on frequency and said; 'traffic eleven o'clock climbing'! [While] looking for the traffic; the target turned red on our TCAS. First officer disconnected the autopilot autothrottles and started a climbing right turn.[while starting] the maneuver; we got an RA. The closure rate of the target was so fast and not being able to obtain a visual I told first officer to 'increase bank; increase bank; increase bank'! He rolled the aircraft in to a 45-50 degree bank! Not obtaining visual and with the azimuth on the navigational display it is hard to judge just how close mileage wise (it was close) the target came to us; but TCAS said it came within 200 feet! The whole episode lasted about 10 seconds!once the RA was over and we were 'clear of conflict' we descended to our assigned altitude turned left joined the localizer; made the approach and landing without further incident! In debriefing we were in agreement the other aircraft must have been fast as the closure rate was very fast. We also believe the other aircraft took off as satellite airport; which is just west of the approach course. For the controller not to instruct us to descend 3;000 feet and join the localizer when he was advised we were flying an RA!

Original NASA ASRS Text

Title: B737 NG flight crew reported that they had a near miss while intercepting the localizer on approach.

Narrative: We had a near miss on approach! Flying a Westerly heading the Approach Controller told us to 'turn right 010; intercept the localizer; descend maintain 3;000 feet until established cleared ILS'. In our turn and descending; the Approach Controller came on frequency and said; 'TRAFFIC eleven o'clock climbing'! [While] looking for the traffic; the target turned red on our TCAS. First Officer disconnected the autopilot autothrottles and started a climbing right turn.[While starting] the maneuver; we got an RA. The closure rate of the target was so fast and not being able to obtain a visual I told First Officer to 'Increase Bank; Increase Bank; Increase Bank'! He rolled the aircraft in to a 45-50 degree bank! Not obtaining visual and with the azimuth on the Navigational Display it is hard to judge just how close mileage wise (it was close) the target came to us; but TCAS said it came within 200 feet! The whole episode lasted about 10 seconds!Once the RA was over and we were 'Clear of Conflict' we descended to our assigned altitude turned left joined the localizer; made the approach and landing without further incident! In debriefing we were in agreement the other aircraft must have been fast as the closure rate was very fast. We also believe the other aircraft took off as satellite airport; which is just west of the approach course. For the Controller not to instruct us to descend 3;000 feet and join the localizer when he was advised we were flying an RA!

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.