A B727 flight crew while deviating for WX, inadvertently descends 300 ft from assigned altitude.

Attributes
ACN	581969
Time
Date	200305
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : fll.airport
State Reference	FL
Altitude	msl single value : 7000
Environment
Flight Conditions	Mixed
Weather Elements	Thunderstorm
Aircraft 1
Controlling Facilities	tower : mia.tower
Operator	common carrier : air carrier
Make Model Name	B727 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Route In Use	arrival : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : mia.tracon
Operator	common carrier : air carrier
Make Model Name	Airbus Industrie Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Route In Use	approach : traffic pattern
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 2300 flight time type : 1500
ASRS Report	581969
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance Environmental Factor Aircraft Weather
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Being vectored on downwind for runway 9L in fll, thunderstorm cell moving into flight path. We dispatched with radar inoperative. We were heading for the cell. First officer was flying. I called approach for a left deviation. It was approved. When coming around the cell I saw airbus turning base for runway 9L. When I looked back into the cockpit saw that the first officer descended 200-300 ft below assigned altitude. I immediately corrected by pulling the yoke and regaining correct altitude. Had we not dispatched with radar inoperative my focus could have stayed in the cockpit. If TCASII had been installed this would also have helped.

Original NASA ASRS Text

Title: A B727 FLT CREW WHILE DEVIATING FOR WX, INADVERTENTLY DSNDS 300 FT FROM ASSIGNED ALT.

Narrative: BEING VECTORED ON DOWNWIND FOR RWY 9L IN FLL, TSTM CELL MOVING INTO FLT PATH. WE DISPATCHED WITH RADAR INOP. WE WERE HEADING FOR THE CELL. FO WAS FLYING. I CALLED APCH FOR A L DEV. IT WAS APPROVED. WHEN COMING AROUND THE CELL I SAW AIRBUS TURNING BASE FOR RWY 9L. WHEN I LOOKED BACK INTO THE COCKPIT SAW THAT THE FO DSNDED 200-300 FT BELOW ASSIGNED ALT. I IMMEDIATELY CORRECTED BY PULLING THE YOKE AND REGAINING CORRECT ALT. HAD WE NOT DISPATCHED WITH RADAR INOP MY FOCUS COULD HAVE STAYED IN THE COCKPIT. IF TCASII HAD BEEN INSTALLED THIS WOULD ALSO HAVE HELPED.

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.