Medium Large Transport
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 70; Flight Crew Total 17000; Flight Crew Type 5000
Communication Breakdown
ATC Issue All Types; Conflict NMAC
Human Factors; Airspace Structure
We were heading 315 degrees away from the LAX VOR on our assigned vector inbound to BUR; we were at 5;000 feet.SoCal Approach Control called out traffic at our 12 o'clock and approximately four miles. The traffic was at 4;500 feet in the Los Angeles Special Flight Rules Area on our same general heading and speed. This target was clearly displayed as a proximate TCAS target on our displays and was in the location described. There was a slight discrepancy in that the target indicated a steady 400 feet below our altitude rather than 500 feet below.We suddenly began receiving audible 'Traffic; Traffic' calls from the TCAS system. These calls were followed quickly by a 'Descend; Descend' audible and an Attitude Direction Indicator (ADI) command calling for a descent. We were in clear weather with unlimited visibility and were experiencing a pitch command to descend into a proximate target.We informed approach that we were receiving a RA to descend. The response was that there was 12 o'clock traffic ahead and below us.Before long an oncoming aircraft appeared visually at 12 o'clock above us and it went overhead. A threat indication appeared on our displays as it passed overhead. The threat indication showed an altitude 400 feet above us. The target and conflict alerts quickly cleared once the southbound aircraft was past.The incident was again reported to ATC and again they reported the aircraft below us. We emphasized that an aircraft had passed above us. We were told that the second aircraft had been 500 feet above us and was speaking to a different controller.The clear weather allowed us to visually maintain a flight path clear of conflicts ahead of us; despite aircraft indicating 400 feet above and below us. We received TCAS system commands to descend towards an aircraft that was below us while receiving no TCAS target displays or ATC notifications until the second; threat aircraft; was passing overhead. The reality of the situation seems to be that all aircraft were essentially properly controlled; in proper positions and that apparently; the variations in altitude transmissions caused an alert.
Corporate jet Captain reported traffic above and below the aircraft flight path in the LAX area which triggered an alert on the TCAS.