Date: 201211
Local time of day: 1201-1800
Location: BUR.Airport, CA
Flight conditions: Mixed
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
ATC / advisory: TRACON SCT
Second aircraft: Aerobatic
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Second reporter function: Pilot Flying; Captain
Anomaly: Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude
Detector: Automation Aircraft RA; Automation Aircraft TA; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Contributing factors: Airspace Structure; Human Factors; Weather
Primary problem: Ambiguous

Narrative: While on approach to BUR; I was the Pilot Monitoring. We were issued a heading and a decent from 6;000 feet to 5;000 feet. ATC advised traffic at one o'clock and five miles. We advised traffic was not in sight due to being in and out of IMC. ATC issued another vector and advised traffic appeared to be descending and at one mile. As we broke out of the clouds; the traffic was in front of us (moving right to left) in a rapid descending left turn. Immediately the TCAS called Traffic and Descend. The Captain kicked off the autopilot and pitched down and turned hard right to avoid the traffic. We estimate that we came within 200 feet vertical and 500 feet horizontal from the other aircraft. We leveled off at 4;000 feet and 10-20 degrees from our assigned heading. I advised ATC that we maneuvered in response to an RA and remained at 4000 feet. We continued and landed in BUR with no further issues. Hard to say what could have prevented this incident. The other aircraft was not talking to ATC and made several rapid maneuvers; apparently to avoid clouds. The TCAS system worked. We responded in a timely manner to avoid a collision.


Second narrative: Our aircraft was on a 170 degree heading at 5;000 feet MSL. We were IMC and on a vector off of the LYNXX 8 STAR into BUR. We had previously received a TCAS TA from traffic that had leveled off at 6;000 feet MSL. Our heading had placed us over terrain that peaked at 3;800 feet MSL (Oat Mountain); which was about 13 NM NW of BUR. Simultaneously; SoCal issued a Traffic Alert for that same traffic; we entered VMC conditions and spotted the traffic (appeared to be a Stearman); a TCAS RA 'Descend; Descend;' which was followed immediately by an 'Increase Descent.' I disengaged the autopilot and autothrust and began a descent; but immediately increased descent rate with the 'Increase Descent' call from the TCAS. The non-communicating traffic appeared to be 'scud running' by starting a sharp descending turn in front of us and heading southeast. I descended to 4;000 feet MSL with an avoidance turn to a heading of 190. In the commotion; my First Officer and I never heard the 'Clear of Conflict' call; but the display was clear. We advised SoCal of the deviation and our heading/altitude. The Controller cleared us to maintain 4;000 feet MSL with a vector to intercept the ILS to Runway 8. The Controller advised us that the traffic was inbound to VNY and was going to get a talking to by the Tower. We continued the approach and landing without further incident.


Synopsis: B737 flight crew reports taking evasive action for a TCAS RA during descent into BUR. Clouds obscured visual contact with the other aircraft until the first TCAS resolution had been enunciated.