A319
Flight Crew Last 90 Days 240; Flight Crew Total 18000; Flight Crew Type 7000
Conflict NMAC
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Human Factors
We were flying into SNA on the KAYOH 5 arrival to Runway 19R. During the arrival at 8;000 feet; SoCal vectored the flight off the STAR to a 290 degree heading. After assigning the heading; SoCal indicated that there was traffic at 12 to 1 o'clock; but; the traffic's altitude was unverified.  Both the Captain and First Officer looked for the traffic in the direction given by ATC. Seeing nothing; the crew looked at the TCAS. No targets were shown on the TCAS. The First Officer had been hand flying the aircraft since 18;000 feet on a clear; sunny; late afternoon. SoCal then issued a clearance to slow to 190 knots; then; descend to 6;600 feet. The First Officer started to slow from 220 knots at idle power; and; at 190 knots started to descend to 6;600 feet. About this time; SoCal again stated there was traffic at 12-1 o'clock; altitude unverified. The Captain was the first to notice the aircraft immediately followed by the First Officer gaining visual. The traffic was less than a mile at 1 o'clock nose on. The Piper Aircraft flew directly over us at about 8;000 feet. Once the traffic passed; the First Officer noted that the altimeter was passing 7;600 feet and still in our descent. Our planes missed by 300-500 feet.  The aircrew informed SoCal of the near miss. SoCal indicated that his radar scope still had no transponder readout from the civilian aircraft.  Upon landing; the Captain called the SoCal Supervisor. Per the SoCal Supervisor; the aircraft had previously violated Class B Airspace at LAX as well. Now the same aircraft was in the arrival corridor to SNA. SoCal had no communication with the aircraft we had passed.
SoCal then issued instructions to; 'Slow to 190 knots; then; descend to 6;600 feet.' The pilot flying started to slow from 220 knots at idle power; and at 190 knots started to descend to 6;600 feet. About this time; SoCal again stated there was traffic at '12-1 o'clock; altitude un-verified.' The pilot monitoring sat up higher in the seat and scanned outside and down from the flight deck window for the traffic. It was at this time that the pilot monitoring noticed movement up and in front of the pilot flying's cockpit window. The movement was a low-wing; fixed gear aircraft who flew by us at our recently vacated 8;000 foot altitude. At this time; our aircraft was at 7;600 feet. He missed our plane by 300-500 feet. NOTE: In my opinion; if the pilot flying was using the A319 autopilot for this maneuver (instead of hand-flying) the slight autopilot delay for slowing and initiating the descent may have put the flight in even closer proximity to the low-wing aircraft. The aircrew informed SoCal of the near miss. SoCal indicated that his radar scope still had no transponder readout from the civilian aircraft. Upon landing; the Captain called the SoCal Supervisor. Per the SoCal Supervisor; the aircraft had previously violated Class B Airspace at LAX as well.
A319 flight crew experiences a NMAC descending out of 8;000 feet during the KAYOH 5 arrival to SNA. The intruder was a fixed gear Piper eastbound at 8;000 feet without a transponder and had reportedly passed through LAX Class B earlier without a clearance to do so.