Narrative:

I was the PF on flight to phx. This was my 4TH leg on the second day of a 3-DAY trip. The original first officer was replaced by reserve first officer's. The first officer on this leg was the 3RD first officer in 2 days, the 2ND this day. He is a new hire from a class 5 months ago and still on probation. His performance was good as per company SOP. The flight was normal, except we step climbed 1000 ft or 2000 ft at a time up to FL180. Level at FL180, we received the clearance 'cleared direct trm, climb to FL220.' I heard and acknowledged FL220. The first officer dialed FL220 in the altitude alerter and I heard the first officer read back the clearance, 'direct trm climb to FL220.' I initiated a climb using vertical speed made with the flight director and autoplt. Passing through FL213, center said, 'maintain FL210.' I disengaged vertical speed mode and pushed the nose over to descend to FL210. Reaching FL210, I engaged altitude hold. I don't remember if I reset the altitude alerter to FL210. I think I did. Center pointed out a slightly slower A320 about 11 O'clock position, and 3 mi at FL220, slowly climbing. I had checked the vsi as we descended to FL210 and saw a solid white diamond 600 ft above us at around 2 1/2-3 mi. No aural warning was heard. I asked the controller if we had mistaken our clearance and he replied 'I don't know.' after a later climb clearance and handoff, the next sector controller advised us to call the center about a possible altitude deviation.

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Original NASA ASRS Text

Title: B735 DEPARTING SNA CLBS TO ATC ASSIGNED ALT WHICH RESULTS IN LOSS OF SEPARATION.

Narrative: I WAS THE PF ON FLT TO PHX. THIS WAS MY 4TH LEG ON THE SECOND DAY OF A 3-DAY TRIP. THE ORIGINAL FO WAS REPLACED BY RESERVE FO'S. THE FO ON THIS LEG WAS THE 3RD FO IN 2 DAYS, THE 2ND THIS DAY. HE IS A NEW HIRE FROM A CLASS 5 MONTHS AGO AND STILL ON PROBATION. HIS PERFORMANCE WAS GOOD AS PER COMPANY SOP. THE FLT WAS NORMAL, EXCEPT WE STEP CLBED 1000 FT OR 2000 FT AT A TIME UP TO FL180. LEVEL AT FL180, WE RECEIVED THE CLRNC 'CLRED DIRECT TRM, CLB TO FL220.' I HEARD AND ACKNOWLEDGED FL220. THE FO DIALED FL220 IN THE ALT ALERTER AND I HEARD THE FO READ BACK THE CLRNC, 'DIRECT TRM CLB TO FL220.' I INITIATED A CLB USING VERT SPD MADE WITH THE FLT DIRECTOR AND AUTOPLT. PASSING THROUGH FL213, CTR SAID, 'MAINTAIN FL210.' I DISENGAGED VERT SPD MODE AND PUSHED THE NOSE OVER TO DSND TO FL210. REACHING FL210, I ENGAGED ALT HOLD. I DON'T REMEMBER IF I RESET THE ALT ALERTER TO FL210. I THINK I DID. CTR POINTED OUT A SLIGHTLY SLOWER A320 ABOUT 11 O'CLOCK POS, AND 3 MI AT FL220, SLOWLY CLBING. I HAD CHKED THE VSI AS WE DSNDED TO FL210 AND SAW A SOLID WHITE DIAMOND 600 FT ABOVE US AT AROUND 2 1/2-3 MI. NO AURAL WARNING WAS HEARD. I ASKED THE CTLR IF WE HAD MISTAKEN OUR CLRNC AND HE REPLIED 'I DON'T KNOW.' AFTER A LATER CLB CLRNC AND HDOF, THE NEXT SECTOR CTLR ADVISED US TO CALL THE CTR ABOUT A POSSIBLE ALTDEV.

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.