B737 CREW HAD AN ALTDEV.

Narrative

ACR ABC WAS ON A DOWNWIND VECTOR FOR RWY 9L AT FLL. ASSIGNED HDG WAS 280 DEGS AND ACR ABC WAS DSNDING FROM 5000 FT TO 4000 FT. DURING DSCNT AND WAKE LEVEL AT 4000 FT; ACR ABC CREW WAS CONCERNED ABOUT TFC AT 9 O'CLOCK LESS THAN 3 MI AND 12 O'CLOCK AT APPROX 5 MI AS DEPICTED BY TCASII. MIA APCH THEN VECTORED ACR ABC L TO A 180 DEG HDG. THE CAPT AND FO WERE STILL CONCERNED ABOUT THE CLOSE PROX OF OTHER TFC. MIA APCH WAS EXTREMELY BUSY AND DID NOT ADEQUATELY PROVIDE ACR ABC WITH TFC CALLS. CONFUSION AROSE ABOUT AN APCH CLRNC. THE FO READ BACK AN APCH CLRNC FOR ANOTHER ACFT. MIA CORRECTED ACR ABC AT APPROX XA34; WHILE HDG S; THE CAPT DSNDED FLT ACR ABC MOMENTARILY TO 3600 FT THINKING THE APCH CLRNC WAS GRANTED FOR ACR ABC. MIA APCH PROMPTLY CORRECTED ACR ABC AND THE CAPT IMMEDIATELY CLBED TO 4000 FT; ASSIGNED ALT. THE FO'S ATTN WAS FOCUSED ON THE TCASII DISPLAY AND THE TFC OUTSIDE THE ACFT. WHEN THE ALTDEV WAS BROUGHT TO THE ATTN OF ACR ABC; THE MCP ALT AND ALTIMETER WERE IMMEDIATELY CHKED. THE MCP HAD 4000 FT SET AND THE ALTIMETER INDICATED 3600 FT. DURING THIS EVENT THE CAPT WAS HAND FLYING THE ACFT AND WAS DISTR BY THE TCASII DISPLAY. THE FO WAS ALSO LOOKING AT THE TCASII DISPLAY AND OUTSIDE THE ACFT; NOT THE ALTIMETER. WHEN THE DEV OCCURRED; THE CREW WAS ESSENTIALLY FOCUSED ON THE SAME TASK. THIS EVENT COULD HAVE BEEN AVOIDED HAD THE CAPT FOCUSED ON HDG AND ALT; USED THE AUTOPLT TO SHED SOME WORKLOAD; THE CTLR KEPT THE AIR CREW BETTER INFORMED ON THE PERTINENT TFC; AND THE FO XCHKED THE ALT WHILE SCANNING THE TCASII DISPLAY. THE CTLR (MIA APCH) APOLOGIZED FOR THE CONFUSION PRIOR TO SWITCHING ACR ABC TO FLL TWR.