Narrative:

I was on an IFR flight plan from mesa, az (ffz) to san diego lindbergh field. Requested altitude was FL200. Between phoenix and yuma (bard) I was traveling west and beginning at 6000' had received incremental clrncs at 2000 or 4000' intervals (mostly 2000) until I was at FL180. I was expecting my clearance from FL180 to be FL200. I had been told there was overtaking traffic at FL200 and assumed I would be held at FL180 until it passed since I was heading west (even altitude). When the clearance came, I misread the instructions of FL190 for FL200. I did not read back. I climbed to FL200 and had set in cruise power. In 2 or 3 mins center advised that traffic was directly overhead. Within less than 1 min, the other plane passed about 400' above and probably 1250' horizontally from me. This is difficult to judge. After the passing, the controller asked that I expedite to FL190. He questioned why I was at FL200 and I immediately realized and acknowledged that my last clearance undoubtedly was FL190. In my mind, I probably followed a pattern of 2000' increments instead of the actual clearance. My conclusions for safer flying: 1) I'll never again accept a clearance without reading back. 2) with the accuracy of mode C xponders, the controller perhaps should have advised me of my error when I was greater than 200 or 300' off my assigned altitude. Most times they are very sensitive to as little as 200' deviation and especially in critical situations. 3) attitude of the controller was excellent, including advising me of the albuquerque phone number if I wished to discuss the incident further. 4) in order to reduce cockpit frustrations of frequent power changes, VFR climbs in VMC conditions should be utilized by pilots and suggested by the controllers.

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Original NASA ASRS Text

Title: SMT INADVERTENTLY CLIMBED ABOVE ASSIGNED ALT AND CONFLICTED WITH SAME DIRECTION TRAFFIC.

Narrative: I WAS ON AN IFR FLT PLAN FROM MESA, AZ (FFZ) TO SAN DIEGO LINDBERGH FIELD. REQUESTED ALT WAS FL200. BETWEEN PHOENIX AND YUMA (BARD) I WAS TRAVELING W AND BEGINNING AT 6000' HAD RECEIVED INCREMENTAL CLRNCS AT 2000 OR 4000' INTERVALS (MOSTLY 2000) UNTIL I WAS AT FL180. I WAS EXPECTING MY CLRNC FROM FL180 TO BE FL200. I HAD BEEN TOLD THERE WAS OVERTAKING TFC AT FL200 AND ASSUMED I WOULD BE HELD AT FL180 UNTIL IT PASSED SINCE I WAS HDG W (EVEN ALT). WHEN THE CLRNC CAME, I MISREAD THE INSTRUCTIONS OF FL190 FOR FL200. I DID NOT READ BACK. I CLIMBED TO FL200 AND HAD SET IN CRUISE POWER. IN 2 OR 3 MINS CENTER ADVISED THAT TFC WAS DIRECTLY OVERHEAD. WITHIN LESS THAN 1 MIN, THE OTHER PLANE PASSED ABOUT 400' ABOVE AND PROBABLY 1250' HORIZONTALLY FROM ME. THIS IS DIFFICULT TO JUDGE. AFTER THE PASSING, THE CTLR ASKED THAT I EXPEDITE TO FL190. HE QUESTIONED WHY I WAS AT FL200 AND I IMMEDIATELY REALIZED AND ACKNOWLEDGED THAT MY LAST CLRNC UNDOUBTEDLY WAS FL190. IN MY MIND, I PROBABLY FOLLOWED A PATTERN OF 2000' INCREMENTS INSTEAD OF THE ACTUAL CLRNC. MY CONCLUSIONS FOR SAFER FLYING: 1) I'LL NEVER AGAIN ACCEPT A CLRNC WITHOUT READING BACK. 2) WITH THE ACCURACY OF MODE C XPONDERS, THE CTLR PERHAPS SHOULD HAVE ADVISED ME OF MY ERROR WHEN I WAS GREATER THAN 200 OR 300' OFF MY ASSIGNED ALT. MOST TIMES THEY ARE VERY SENSITIVE TO AS LITTLE AS 200' DEVIATION AND ESPECIALLY IN CRITICAL SITUATIONS. 3) ATTITUDE OF THE CTLR WAS EXCELLENT, INCLUDING ADVISING ME OF THE ALBUQUERQUE PHONE NUMBER IF I WISHED TO DISCUSS THE INCIDENT FURTHER. 4) IN ORDER TO REDUCE COCKPIT FRUSTRATIONS OF FREQUENT POWER CHANGES, VFR CLIMBS IN VMC CONDITIONS SHOULD BE UTILIZED BY PLTS AND SUGGESTED BY THE CTLRS.

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.