Narrative:

I was instructed to make a right turn to 090 degree, maintain 5000 ft. While in the turn I saw the destination airport and asked for a visual approach. The controller amended the heading to '030 degree, descend to 3000 ft.' I acknowledged, stopped my turn at 030 degree and simultaneously started my descent to 3000 ft. At 4500 ft, the controller very sharply called and said, small transport X I told you to remain at 5000 ft. My passenger, an IFR pilot, who was sitting in the copilot chair, and I exchanged looks of amazement... I immediately climbed back to 5000 ft. I was given 2-3 more heading changes and descent clrncs to a routine landing. During taxi, ground control advised me to call the ontario TRACON. I called and was advised, according to TRACON supervisor, I had started a descent, thought he had told me to remain at 5000 ft. I asked if they had played the tape. They had not yet had time but it appeared I had descended into the path of air carrier Y at 4000 ft, wbound. Since I had another en route stop to make before returning to home base, it was suggested I call TRACON again. I called and the tape confirmed that I had been cleared to 3000 ft although, at first, the controller tried to deny it. Apparently, a student controller who had been observing, confirmed, I had been cleared to 3000 ft, too. I regret the controller made an error. I resent his trying to blame 'the pilot.' I believe many pilots feel, unfortunately, the 'system' often 'tries' to blame pilots when they (pilots) are not at fault.

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Original NASA ASRS Text

Title: SMT X DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM ACR Y. SYS ERROR.

Narrative: I WAS INSTRUCTED TO MAKE A R TURN TO 090 DEG, MAINTAIN 5000 FT. WHILE IN THE TURN I SAW THE DEST ARPT AND ASKED FOR A VISUAL APCH. THE CTLR AMENDED THE HDG TO '030 DEG, DSND TO 3000 FT.' I ACKNOWLEDGED, STOPPED MY TURN AT 030 DEG AND SIMULTANEOUSLY STARTED MY DSCNT TO 3000 FT. AT 4500 FT, THE CTLR VERY SHARPLY CALLED AND SAID, SMT X I TOLD YOU TO REMAIN AT 5000 FT. MY PAX, AN IFR PLT, WHO WAS SITTING IN THE COPLT CHAIR, AND I EXCHANGED LOOKS OF AMAZEMENT... I IMMEDIATELY CLBED BACK TO 5000 FT. I WAS GIVEN 2-3 MORE HDG CHANGES AND DSCNT CLRNCS TO A ROUTINE LNDG. DURING TAXI, GND CTL ADVISED ME TO CALL THE ONTARIO TRACON. I CALLED AND WAS ADVISED, ACCORDING TO TRACON SUPVR, I HAD STARTED A DSCNT, THOUGHT HE HAD TOLD ME TO REMAIN AT 5000 FT. I ASKED IF THEY HAD PLAYED THE TAPE. THEY HAD NOT YET HAD TIME BUT IT APPEARED I HAD DSNDED INTO THE PATH OF ACR Y AT 4000 FT, WBOUND. SINCE I HAD ANOTHER ENRTE STOP TO MAKE BEFORE RETURNING TO HOME BASE, IT WAS SUGGESTED I CALL TRACON AGAIN. I CALLED AND THE TAPE CONFIRMED THAT I HAD BEEN CLRED TO 3000 FT ALTHOUGH, AT FIRST, THE CTLR TRIED TO DENY IT. APPARENTLY, A STUDENT CTLR WHO HAD BEEN OBSERVING, CONFIRMED, I HAD BEEN CLRED TO 3000 FT, TOO. I REGRET THE CTLR MADE AN ERROR. I RESENT HIS TRYING TO BLAME 'THE PLT.' I BELIEVE MANY PLTS FEEL, UNFORTUNATELY, THE 'SYS' OFTEN 'TRIES' TO BLAME PLTS WHEN THEY (PLTS) ARE NOT AT FAULT.

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.