PLTDEV WHEN AN ACR B737 CLBED 300 FT ABOVE ASSIGNED ALT OF 10000 FT AND CONFLICTED WITH A DSNDING ACR FK10. LTSS.

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FLT DEPARTED LOVE FIELD NORMALLY TO MIDLAND AND WERE GIVEN VECTORS FOR THE SID. BUSY TFC AND WAS GIVEN NUMEROUS TA'S FROM ZFW. WE WERE CLRED TO CLB 10000 FT AND ALSO ADVISED OF TFC AT OUR 10-11 O'CLOCK POS AND TFC DSNDING AT OUR 12-1 O'CLOCK POS. I ADVISED LOOKING FOR TFC. CAPT WAS FLYING THE PARTICULAR LEG AND FO (ME) MONITOR THE RADIO. AT 9000 FT WE BOTH SAID 1000 FT TO GO TILL WE REACH 10000 FT. I LOOKED AT OUR TCASII TO FIND TFC WHICH WE WERE ADVISED OF AND I ALSO LOOKED OUTSIDE TO FIND OR SEE THE TFC DSNDING. THEN WE RECEIVED TCASII RA AND I LOOKED AT OUR RADAR ALTIMETER AND CAPT BUSTED 10000 FT AND INSTEAD WE WERE AT 10300 FT. CAPT CORRECTED IMMEDIATELY AND DSNDED BACK TO 10000 FT AND AT THE SAME TIME; WE BOTH NOTICED THE OTHER TFC. ATC THEN AGAIN SAID TFC AT 12 O'CLOCK. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THEIR ACFT DID NOT HAVE ALT HOLD AND WHILE THE FLC WERE LOOKING FOR THE TFC; THE PF WENT THROUGH 10000 FT. RPTR SAID THEY HAD THE FOKKER IN SIGHT AND THAT THE CTLR DID NOT SAY ANYTHING ABOUT A LOSS OF SEPARATION BTWN THE 2 ACFT.