Narrative:

The copilot checked in with ont tower at 11 mi DME and medium large transport was #1 and cleared to land on runway 26R. At fonta, the OM for both 26 runways, and on G/south, the copilot remarked, 'hey, look at that.' at our 1 O'clock position, about/maybe 500' below us, a light twin passed from left to right in a steep right turn. I asked ont tower if there was any other traffic in our area. She answered, 'not to my knowledge.' I told her what we had seen. At the gate one very concerned passenger asked if we had seen that aircraft. I called ont tower and the young lady informed me that she had no control over aircraft in that airspace. Callback conversation with reporter revealed the following: neither TRACON nor the tower would admit seeing a target on their radar. The light twin obviously did not have transponder on and was just below the floor of the outer area of the arsa, but was quite probably in the inner ring of arsa which extends from surface. Reporter expects to hear nothing further from incident as controller was unconcerned.

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Original NASA ASRS Text

Title: POTENTIAL CONFLICT BETWEEN ACR-MLG ON APCH AND SMA NEAR LOCALIZER AND GLIDE SLOPE.

Narrative: THE COPLT CHKED IN WITH ONT TWR AT 11 MI DME AND MLG WAS #1 AND CLRED TO LAND ON RWY 26R. AT FONTA, THE OM FOR BOTH 26 RWYS, AND ON G/S, THE COPLT REMARKED, 'HEY, LOOK AT THAT.' AT OUR 1 O'CLOCK POS, ABOUT/MAYBE 500' BELOW US, A LIGHT TWIN PASSED FROM LEFT TO RIGHT IN A STEEP RIGHT TURN. I ASKED ONT TWR IF THERE WAS ANY OTHER TFC IN OUR AREA. SHE ANSWERED, 'NOT TO MY KNOWLEDGE.' I TOLD HER WHAT WE HAD SEEN. AT THE GATE ONE VERY CONCERNED PAX ASKED IF WE HAD SEEN THAT ACFT. I CALLED ONT TWR AND THE YOUNG LADY INFORMED ME THAT SHE HAD NO CTL OVER ACFT IN THAT AIRSPACE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: NEITHER TRACON NOR THE TWR WOULD ADMIT SEEING A TARGET ON THEIR RADAR. THE LIGHT TWIN OBVIOUSLY DID NOT HAVE TRANSPONDER ON AND WAS JUST BELOW THE FLOOR OF THE OUTER AREA OF THE ARSA, BUT WAS QUITE PROBABLY IN THE INNER RING OF ARSA WHICH EXTENDS FROM SURFACE. RPTR EXPECTS TO HEAR NOTHING FURTHER FROM INCIDENT AS CTLR WAS UNCONCERNED.

Data retrieved from NASA's ASRS site as of August 2007 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.