Narrative:

As we neared vero beach airport for landing the crew was dealing with a couple of aircraft problems including inoperative pilot side windshield heat control and cabin overpressurization. We had been told to expect a visibility approach into the busy, sea level vero beach airport as soon as we cleared an small aircraft also in contact with mia. We told center we had visibility contact with the non-conflicting aircraft and had the airport in sight. Copilot was consulting emergency checklist for overpressurization as the captain was trying to control pressurization with throttle reduction. At that moment ATC told us to 'line up for downwind.' since we were well past previous traffic, almost on top of the airport, concerned about maintaining visibility contact with VFR traffic at this airport and about to enter a broken cloud layer, the PF construed the controller's instruction to mean enter this landing pattern. He then descended from 5000' and was advised by ATC at 4000' that they felt an altitude excursion had occurred. Since we were abnormally busy and copilot's attention was diverted, copilot did not notice captain descending and was unable to query captain or ATC in time re: proper altitude. If the pilot misunderstood ATC, copilot was, at least, equally responsible for monitoring captain's compliance with ATC. The crew feels that since we were literally entering the downwind leg for landing at a busy VFR sea level airport, if the center controller advised 'line up for the downwind,' he might also have reiterated 'maintain 5000'' since it would not normally be a standard altitude for our position.

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Original NASA ASRS Text

Title: SMT ON VECTORS TO A VISUAL APCH LEFT ASSIGNED ALT.

Narrative: AS WE NEARED VERO BEACH ARPT FOR LNDG THE CREW WAS DEALING WITH A COUPLE OF ACFT PROBS INCLUDING INOP PLT SIDE WINDSHIELD HEAT CONTROL AND CABIN OVERPRESSURIZATION. WE HAD BEEN TOLD TO EXPECT A VIS APCH INTO THE BUSY, SEA LEVEL VERO BEACH ARPT AS SOON AS WE CLRED AN SMA ALSO IN CONTACT WITH MIA. WE TOLD CENTER WE HAD VIS CONTACT WITH THE NON-CONFLICTING ACFT AND HAD THE ARPT IN SIGHT. COPLT WAS CONSULTING EMER CHKLIST FOR OVERPRESSURIZATION AS THE CAPT WAS TRYING TO CONTROL PRESSURIZATION WITH THROTTLE REDUCTION. AT THAT MOMENT ATC TOLD US TO 'LINE UP FOR DOWNWIND.' SINCE WE WERE WELL PAST PREVIOUS TFC, ALMOST ON TOP OF THE ARPT, CONCERNED ABOUT MAINTAINING VIS CONTACT WITH VFR TFC AT THIS ARPT AND ABOUT TO ENTER A BROKEN CLOUD LAYER, THE PF CONSTRUED THE CTLR'S INSTRUCTION TO MEAN ENTER THIS LNDG PATTERN. HE THEN DSNDED FROM 5000' AND WAS ADVISED BY ATC AT 4000' THAT THEY FELT AN ALT EXCURSION HAD OCCURRED. SINCE WE WERE ABNORMALLY BUSY AND COPLT'S ATTN WAS DIVERTED, COPLT DID NOT NOTICE CAPT DSNDING AND WAS UNABLE TO QUERY CAPT OR ATC IN TIME RE: PROPER ALT. IF THE PLT MISUNDERSTOOD ATC, COPLT WAS, AT LEAST, EQUALLY RESPONSIBLE FOR MONITORING CAPT'S COMPLIANCE WITH ATC. THE CREW FEELS THAT SINCE WE WERE LITERALLY ENTERING THE DOWNWIND LEG FOR LNDG AT A BUSY VFR SEA LEVEL ARPT, IF THE CENTER CTLR ADVISED 'LINE UP FOR THE DOWNWIND,' HE MIGHT ALSO HAVE REITERATED 'MAINTAIN 5000'' SINCE IT WOULD NOT NORMALLY BE A STANDARD ALT FOR OUR POS.

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.