Narrative:

While on vectors with phl approach control we were issued a clearance to descend from 7000 ft MSL to 6000 ft. Ride was rough, moderate chop to moderate turbulence and rain, with no thunderstorm activity noted on radar. Shortly after initiating the descent we encountered a 'downdraft' that, while not violent, required higher than normal power settings to counter. We reported 'unable to hold 6000 ft' to ATC and subsequently leveled off at 5500 ft. Approach control acknowledged and advised to return to 6000 ft when able. We regained 6000 ft in about 45-60 seconds. I believe we may have passed through a squall line. However, severity was not indicated by radar presentation, PIREP, or ATC.

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Original NASA ASRS Text

Title: A DSNDING B737-200 SUFFERS A LOSS OF ACFT CTL WHILE ENCOUNTERING A DOWNDRAFT AND TURB. IT OVERSHOT ITS ASSIGNED ALT BY 500 FT.

Narrative: WHILE ON VECTORS WITH PHL APCH CTL WE WERE ISSUED A CLRNC TO DSND FROM 7000 FT MSL TO 6000 FT. RIDE WAS ROUGH, MODERATE CHOP TO MODERATE TURB AND RAIN, WITH NO TSTM ACTIVITY NOTED ON RADAR. SHORTLY AFTER INITIATING THE DSCNT WE ENCOUNTERED A 'DOWNDRAFT' THAT, WHILE NOT VIOLENT, REQUIRED HIGHER THAN NORMAL PWR SETTINGS TO COUNTER. WE RPTED 'UNABLE TO HOLD 6000 FT' TO ATC AND SUBSEQUENTLY LEVELED OFF AT 5500 FT. APCH CTL ACKNOWLEDGED AND ADVISED TO RETURN TO 6000 FT WHEN ABLE. WE REGAINED 6000 FT IN ABOUT 45-60 SECONDS. I BELIEVE WE MAY HAVE PASSED THROUGH A SQUALL LINE. HOWEVER, SEVERITY WAS NOT INDICATED BY RADAR PRESENTATION, PIREP, OR ATC.

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.