Narrative:

I was the PIC of a scheduled part 135 cargo flight. I departed bfl on an IFR flight plan with ont as my destination. Upon checking in (on top 7500 ft direct pom VORTAC) with socal TRACON on 125.5, I canceled my IFR and continued with radar advisories. The sector controller acknowledged my IFR cancellation, and gave me instructions to 'enter the north downwind for the runway 26 complex, at or above 4000 ft.' I read this instruction back, and started a VFR descent to 4000 ft MSL. After a few mins, the controller cleared me to 'descend at or above 3500 ft.' I acknowledged this with a readback. I was then told to contact ont tower on 120.6 MHZ. I acknowledged this instruction with a readback. I then contacted ont tower. I advised them I was on 'right downwind, restr.' the local ont controller acknowledged my call with the instruction to 'continue your descent, not below 2500 ft.' I read this instruction back 'at or above 2 point 5.' during my descent to 2500 ft, I observed conflicting traffic going opposite direction, approximately 150 ft higher, and 500 ft to my left side. I believe this aircraft was on approach to the nearby poc airport. I thought that the separation was inadequate, so I asked ont local controller to confirm my altitude assignment as 'at or above 2500 ft.' the controller said 'no, 3500 ft.' he then cleared me to land. I am sure I was given the 2500 ft restr. But, it is possible that I misheard my instructions, and he misheard my readback.

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Original NASA ASRS Text

Title: CONFLICT BTWN A DSNDING C208 AND AN UNKNOWN GA ACFT NEAR THE TFC PATTERN ENTRY POINT 2 NM NW OF ONT, CA.

Narrative: I WAS THE PIC OF A SCHEDULED PART 135 CARGO FLT. I DEPARTED BFL ON AN IFR FLT PLAN WITH ONT AS MY DEST. UPON CHKING IN (ON TOP 7500 FT DIRECT POM VORTAC) WITH SOCAL TRACON ON 125.5, I CANCELED MY IFR AND CONTINUED WITH RADAR ADVISORIES. THE SECTOR CTLR ACKNOWLEDGED MY IFR CANCELLATION, AND GAVE ME INSTRUCTIONS TO 'ENTER THE N DOWNWIND FOR THE RWY 26 COMPLEX, AT OR ABOVE 4000 FT.' I READ THIS INSTRUCTION BACK, AND STARTED A VFR DSCNT TO 4000 FT MSL. AFTER A FEW MINS, THE CTLR CLRED ME TO 'DSND AT OR ABOVE 3500 FT.' I ACKNOWLEDGED THIS WITH A READBACK. I WAS THEN TOLD TO CONTACT ONT TWR ON 120.6 MHZ. I ACKNOWLEDGED THIS INSTRUCTION WITH A READBACK. I THEN CONTACTED ONT TWR. I ADVISED THEM I WAS ON 'R DOWNWIND, RESTR.' THE LCL ONT CTLR ACKNOWLEDGED MY CALL WITH THE INSTRUCTION TO 'CONTINUE YOUR DSCNT, NOT BELOW 2500 FT.' I READ THIS INSTRUCTION BACK 'AT OR ABOVE 2 POINT 5.' DURING MY DSCNT TO 2500 FT, I OBSERVED CONFLICTING TFC GOING OPPOSITE DIRECTION, APPROX 150 FT HIGHER, AND 500 FT TO MY L SIDE. I BELIEVE THIS ACFT WAS ON APCH TO THE NEARBY POC ARPT. I THOUGHT THAT THE SEPARATION WAS INADEQUATE, SO I ASKED ONT LCL CTLR TO CONFIRM MY ALT ASSIGNMENT AS 'AT OR ABOVE 2500 FT.' THE CTLR SAID 'NO, 3500 FT.' HE THEN CLRED ME TO LAND. I AM SURE I WAS GIVEN THE 2500 FT RESTR. BUT, IT IS POSSIBLE THAT I MISHEARD MY INSTRUCTIONS, AND HE MISHEARD MY READBACK.

Data retrieved from NASA's ASRS site as of July 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.