Narrative:

Air carrier abc was on a downwind vector for runway 9L at fll. Assigned heading was 280 degrees and air carrier abc was descending from 5000 ft to 4000 ft. During descent and wake level at 4000 ft, air carrier abc crew was concerned about traffic at 9 O'clock less than 3 mi and 12 O'clock at approximately 5 mi as depicted by TCASII. Mia approach then vectored air carrier abc left to a 180 degree heading. The captain and first officer were still concerned about the close proximity of other traffic. Mia approach was extremely busy and did not adequately provide air carrier abc with traffic calls. Confusion arose about an approach clearance. The first officer read back an approach clearance for another aircraft. Mia corrected air carrier abc at approximately XA34, while heading south, the captain descended flight air carrier abc momentarily to 3600 ft thinking the approach clearance was granted for air carrier abc. Mia approach promptly corrected air carrier abc and the captain immediately climbed to 4000 ft, assigned altitude. The first officer's attention was focused on the TCASII display and the traffic outside the aircraft. When the altitude deviation was brought to the attention of air carrier abc, the MCP altitude and altimeter were immediately checked. The MCP had 4000 ft set and the altimeter indicated 3600 ft. During this event the captain was hand flying the aircraft and was distraction by the TCASII display. The first officer was also looking at the TCASII display and outside the aircraft, not the altimeter. When the deviation occurred, the crew was essentially focused on the same task. This event could have been avoided had the captain focused on heading and altitude, used the autoplt to shed some workload, the controller kept the air crew better informed on the pertinent traffic, and the first officer crosschecked the altitude while scanning the TCASII display. The controller (mia approach) apologized for the confusion prior to switching air carrier abc to fll tower.

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Original NASA ASRS Text

Title: 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.

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.