Narrative:

We were executing the ILS runway 27R approach in VMC at metropolitan oakland international airport. The time of the incident was approximately XA20 and although some smog and haze were present; ATIS was reporting the WX as visibility 5 mi in mist and few clouds at FL200. We were cleared to land on runway 27R on initial contact with the tower; and once again with less than 1 mi to landing. I was making the callouts; and my first officer was flying the aircraft. We had 3 passenger on board. Inside 1/2 mi; I called '3 green; cleared to land' when I viewed through my first officer's windscreen a yak 52 aircraft closing from right to left in what appeared to be a tight; right base for runway 27R. The yak 52 was at approximately our same altitude (100-150 ft AGL) and within a horizontal distance of approximately 100-150 ft. I immediately directed my first officer to 'go around' and to pass behind the yak 52 in order to avoid a certain collision. We climbed to pattern altitude and were given permission by the tower to enter a right downwind for an uneventful visual approach and landing back to runway 27R. Afterwards; after discussion with the tower via phone conversation; it was revealed by the tower controller that the yak 52 pilot was doing pattern work and had been cleared to land #2 behind us on runway 27R. At some point during our approach; the yak 52 pilot turned inside of us. When the tower controller realized the 'early turn;' he directed the yak 52 pilot to land on runway 27L instead of runway 27R; obviously across our flight path! Unfortunately; we were not aware that the yak 52 pilot had turned in front of us until it was nearly too late and very nearly out of our control. The go around that we executed was not taken to merely avoid a possible/potential midair; our actions were taken to avoid a 'certain' midair collision with another aircraft! In over 32 yrs of flying; I've never had as close a call as this one!

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Original NASA ASRS Text

Title: C560 EXPERIENCED NMAC ON SHORT FINAL TO OAK WITH UNRPTED GA ACFT.

Narrative: WE WERE EXECUTING THE ILS RWY 27R APCH IN VMC AT METRO OAKLAND INTL ARPT. THE TIME OF THE INCIDENT WAS APPROX XA20 AND ALTHOUGH SOME SMOG AND HAZE WERE PRESENT; ATIS WAS RPTING THE WX AS VISIBILITY 5 MI IN MIST AND FEW CLOUDS AT FL200. WE WERE CLRED TO LAND ON RWY 27R ON INITIAL CONTACT WITH THE TWR; AND ONCE AGAIN WITH LESS THAN 1 MI TO LNDG. I WAS MAKING THE CALLOUTS; AND MY FO WAS FLYING THE ACFT. WE HAD 3 PAX ON BOARD. INSIDE 1/2 MI; I CALLED '3 GREEN; CLRED TO LAND' WHEN I VIEWED THROUGH MY FO'S WINDSCREEN A YAK 52 ACFT CLOSING FROM R TO L IN WHAT APPEARED TO BE A TIGHT; R BASE FOR RWY 27R. THE YAK 52 WAS AT APPROX OUR SAME ALT (100-150 FT AGL) AND WITHIN A HORIZ DISTANCE OF APPROX 100-150 FT. I IMMEDIATELY DIRECTED MY FO TO 'GO AROUND' AND TO PASS BEHIND THE YAK 52 IN ORDER TO AVOID A CERTAIN COLLISION. WE CLBED TO PATTERN ALT AND WERE GIVEN PERMISSION BY THE TWR TO ENTER A R DOWNWIND FOR AN UNEVENTFUL VISUAL APCH AND LNDG BACK TO RWY 27R. AFTERWARDS; AFTER DISCUSSION WITH THE TWR VIA PHONE CONVERSATION; IT WAS REVEALED BY THE TWR CTLR THAT THE YAK 52 PLT WAS DOING PATTERN WORK AND HAD BEEN CLRED TO LAND #2 BEHIND US ON RWY 27R. AT SOME POINT DURING OUR APCH; THE YAK 52 PLT TURNED INSIDE OF US. WHEN THE TWR CTLR REALIZED THE 'EARLY TURN;' HE DIRECTED THE YAK 52 PLT TO LAND ON RWY 27L INSTEAD OF RWY 27R; OBVIOUSLY ACROSS OUR FLT PATH! UNFORTUNATELY; WE WERE NOT AWARE THAT THE YAK 52 PLT HAD TURNED IN FRONT OF US UNTIL IT WAS NEARLY TOO LATE AND VERY NEARLY OUT OF OUR CTL. THE GAR THAT WE EXECUTED WAS NOT TAKEN TO MERELY AVOID A POSSIBLE/POTENTIAL MIDAIR; OUR ACTIONS WERE TAKEN TO AVOID A 'CERTAIN' MIDAIR COLLISION WITH ANOTHER ACFT! IN OVER 32 YRS OF FLYING; I'VE NEVER HAD AS CLOSE A CALL AS THIS ONE!

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.