Narrative:

Reporter; in cessna centurion; was on a VFR flight with flight following from sbp to smo. At time of event; I had recently been handed off from mugu approach to socal lax west sector on 125.2. I was below lax class B airspace descending eastbound along coast line; with lower class B airspace to my right (south). As I approached the malibu canyon area my tis showed an aircraft at a slightly lower altitude and ahead going sbound (from my left to my right). I visually detected the aircraft (a piper cherokee) as it turned eastbound at approximately my 1 O'clock position and 1 mi or so. It was well defined against the ocean. I was overtaking it and planned to pass it to its left. There was adequate terrain clearance to do so; even in descent. Shortly after I saw this aircraft; the controller called it and another aircraft. I never saw this second aircraft; but it passed us. A few moments later; my tis suddenly displayed another aircraft at my altitude ahead and coming toward me and the cherokee. At that point I had descended almost to the same altitude as the cherokee I was overtaking. The controller called this traffic about the same time that I determined its altitude. I pushed the nose down to descend through its altitude (and the cherokee's); turning left slightly toward the terrain to remain clear of the cherokee. The opposite-direction aircraft passed right of and very close to the cherokee -- 50 ft or less horizontally. It appeared to be at the same altitude; but because I was just slightly below and behind the cherokee to the left; the opposite-direction aircraft was probably just slightly above; but not much. My guess was that all 3 aircraft were within 150 ft of each other. We weren't too far from a situation where we all arrived at the same point at the same time. The cherokee pilot apparently didn't see the opposite-direction aircraft (which I couldn't identify) until it was passing him; but he reacted by banking away to the left and toward me; which I anticipated and also turned left toward the terrain. I was abeam of the cherokee at that point; and he appeared to be startled when he saw me. I received a terrain warning as a result of this turn and continuing descent; but there was no actual danger. The cherokee landed at smo shortly after me. I tried to find the pilot after securing my aircraft but was unable to do so.

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Original NASA ASRS Text

Title: C210 PLT HAS AN NMAC DURING DSCNT TO SMO.

Narrative: RPTR; IN CESSNA CENTURION; WAS ON A VFR FLT WITH FLT FOLLOWING FROM SBP TO SMO. AT TIME OF EVENT; I HAD RECENTLY BEEN HANDED OFF FROM MUGU APCH TO SOCAL LAX W SECTOR ON 125.2. I WAS BELOW LAX CLASS B AIRSPACE DSNDING EBOUND ALONG COAST LINE; WITH LOWER CLASS B AIRSPACE TO MY R (S). AS I APCHED THE MALIBU CANYON AREA MY TIS SHOWED AN ACFT AT A SLIGHTLY LOWER ALT AND AHEAD GOING SBOUND (FROM MY L TO MY R). I VISUALLY DETECTED THE ACFT (A PIPER CHEROKEE) AS IT TURNED EBOUND AT APPROX MY 1 O'CLOCK POS AND 1 MI OR SO. IT WAS WELL DEFINED AGAINST THE OCEAN. I WAS OVERTAKING IT AND PLANNED TO PASS IT TO ITS L. THERE WAS ADEQUATE TERRAIN CLRNC TO DO SO; EVEN IN DSCNT. SHORTLY AFTER I SAW THIS ACFT; THE CTLR CALLED IT AND ANOTHER ACFT. I NEVER SAW THIS SECOND ACFT; BUT IT PASSED US. A FEW MOMENTS LATER; MY TIS SUDDENLY DISPLAYED ANOTHER ACFT AT MY ALT AHEAD AND COMING TOWARD ME AND THE CHEROKEE. AT THAT POINT I HAD DSNDED ALMOST TO THE SAME ALT AS THE CHEROKEE I WAS OVERTAKING. THE CTLR CALLED THIS TFC ABOUT THE SAME TIME THAT I DETERMINED ITS ALT. I PUSHED THE NOSE DOWN TO DSND THROUGH ITS ALT (AND THE CHEROKEE'S); TURNING L SLIGHTLY TOWARD THE TERRAIN TO REMAIN CLR OF THE CHEROKEE. THE OPPOSITE-DIRECTION ACFT PASSED R OF AND VERY CLOSE TO THE CHEROKEE -- 50 FT OR LESS HORIZONTALLY. IT APPEARED TO BE AT THE SAME ALT; BUT BECAUSE I WAS JUST SLIGHTLY BELOW AND BEHIND THE CHEROKEE TO THE L; THE OPPOSITE-DIRECTION ACFT WAS PROBABLY JUST SLIGHTLY ABOVE; BUT NOT MUCH. MY GUESS WAS THAT ALL 3 ACFT WERE WITHIN 150 FT OF EACH OTHER. WE WEREN'T TOO FAR FROM A SITUATION WHERE WE ALL ARRIVED AT THE SAME POINT AT THE SAME TIME. THE CHEROKEE PLT APPARENTLY DIDN'T SEE THE OPPOSITE-DIRECTION ACFT (WHICH I COULDN'T IDENT) UNTIL IT WAS PASSING HIM; BUT HE REACTED BY BANKING AWAY TO THE L AND TOWARD ME; WHICH I ANTICIPATED AND ALSO TURNED L TOWARD THE TERRAIN. I WAS ABEAM OF THE CHEROKEE AT THAT POINT; AND HE APPEARED TO BE STARTLED WHEN HE SAW ME. I RECEIVED A TERRAIN WARNING AS A RESULT OF THIS TURN AND CONTINUING DSCNT; BUT THERE WAS NO ACTUAL DANGER. THE CHEROKEE LANDED AT SMO SHORTLY AFTER ME. I TRIED TO FIND THE PLT AFTER SECURING MY ACFT BUT WAS UNABLE TO DO SO.

Data retrieved from NASA's ASRS site as of January 2009 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.